Dr. Jeff Masters' WunderBlog

Caribbean disturbance very unimpressive; Arizona watches Otis

By: JeffMasters, 9:03 PM GMT on September 30, 2005

Caribbean disturbance
The tropical disturbance in the western Caribbean Sea has lost almost all of its deep convection this afternoon, and is not a threat to develop into a tropical depression today. Surface pressures are still falling over this area (see the pressure plot from buoy 42056 about 100 miles southeast of Cancun, Mexico), and the disturbance still has a well-defined surface circulation. However, unless the disturbance can fire up some more deep convection by midnight tonight, it will probably totally fall apart and no longer be a threat to the Gulf Coast.

Wind shear over the system is mostly unchanged at 5 - 10 knots, but a slight bit of extra shear from easterly winds blowing from the Yucatan Peninsula has disrupted the system this afternoon. There is no real change to the forecast--shear is expected to remain the same or decrease as the system moves northwest towards the Yucatan Peninsula or Western Cuba. Given the disturbance's almost total lack of deep convection, Sunday is the earliest I would expect it to be able to develop into a depression. The odds are now 40% at best that this system will develop into a depression at all.

If the system does manage to develop, the Mexican Gulf Coast or Texas look like the most likely targets. The GFDL, which forecasted intensification into a Category 1 hurricane with last night's run, now says the disturbance won't develop at all. Only the Canadian model thinks the disturbance will develop. This model takes the system into the Texas/Mexican border region on Tuesday.


Figure 1. BAMM and GFDL track forecasts.

Hurricane Otis threatening Baja and Arizona
Arizona and Mexico's Baja Peninsula are watching Hurricane Otis, which is strengthening as moves northwest parallel to the Baja Peninsula. Otis is currently a Category 1 hurricane with top winds of 85 mph, but is steadily strengthening, and could attain Category 3 status on Saturday. A wind speed of 46 mph with a gust to 61 mph was reported at Cabo San Lucas on the southern tip of the Baja Peninsula today.


Figure 2. Hurricane Otis.

Otis is taking a path very close to the Baja coast, where a narrow tongue of warm water will enable it to maintain hurricane intensity at a much further north point than most East Pacific hurricanes are able to. A hurricane watch has been issued for much of the Baja Peninsula, and this will be upgraded to a hurricane warning on Saturday. Otis is expected to cross the Baja Peninsula Sunday, and quickly weaken to a tropical storm as it moves up the Gulf of California towards Arizona. By Monday, the remains of Otis should cause 3 - 5 inches of rain to fall over southern Arizona, creating flash flooding problems.

TD 19
The tropical disturbance about 600 miles west-southwest of the Cape Verde Islands developed an impressive blow-up of thunderstorms near its center of circulation this afternoon. With good spiral banding and upper-level outflow channels beginning to form, NHC decided to upgrade this system to Tropical Depression 19. This depression has a favorable environment to strengthen, and will become Tropical Storm Stan on Saturday, and probably Hurricane Stan early next week. The system is expected to move slowly northwest for the next five days and not threaten any land areas.

Southeast U.S.
Several of the global computer models continue to forecast that a tropical storm may form near the Bahama Islands on Monday or Tuesday. Any system forming in this region would be forced westward or west-southwestward into the Southeast Coast by a strong ridge of high pressure building in. There are no signs yet of any development occurring in the Bahamas, and the chances of a tropical storm forming in this region as forecast are probably around 20%.

Hawaii
Tropical Depression Kenneth dissipated 35 miles east of the Big Island. The remnants of Kenneth will bring heavy rains and the threat of flash flooding to the islands Saturday.

China
Super Typhoon Langwang, a small but intense typhoon with 140 mph sustained winds, is headed towards China and may hit Taiwan as a Category 3 storm on Sunday. Longwang is expected to gradually weaken but still hit mainland China on Monday as a Category 1 storm.

Jeff Masters

Updated: 9:15 PM GMT on September 30, 2005

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No change to Caribbean disturbance

By: JeffMasters, 1:46 PM GMT on September 30, 2005

The tropical disturbance in the western Caribbean Sea remains disorganized, but has a large area of thunderstorms covering an area from Cuba to Honduras to Jamaica associated with it. Surface pressures are falling over this area. For example, a pressure/wind plot from buoy 42056 about 100 miles southeast of Cancun, Mexico shows a steady drop in pressure the past two days (with an oscillation due to the daily pressure wave triggered by solar heating of the atmosphere also seen). However, the surface circulation center is weak and displaced to the southwest of the main convection, and there is poor upper-level outflow and no sign of low-level spiral banding.

Wind shear over the system is unchanged at 5 - 10 knots, and is forecast to remain the same or decrease as the system moves northwest towards the Yucatan Peninsula or Western Cuba. I still expect this system to eventually develop into a tropical depression, but not today. The hurricane hunters are on call today in case some dramatic development starts to occur, though. A small upper-level anticyclone remains over the system, and this favorable upper-level wind pattern is forecast to persist for the next few days. The system has plenty of moist air surrounding it, and will continue to do so for at least one more day. As the system moves closer to the Gulf of Mexico, it will have some dry air to contend with, since the Gulf is filled with relatively dry air, and there is always dry air over the high plateaus of the Yucatan that might get sucked in.

If the system does manage to develop, the Mexican Gulf Coast or Texas look like the most likely targets. The only model that develops the system into a tropical storm is the GFDL, which forecasts a motion past the tip of the Yucatan Peninsula northwestward, then a turn to the west-southwest as a strong ridge of high pressure builds over the Gulf of Mexico. The GFDL forecasts intensification into a Category 1 hurricane and a strike on the Mexican coast south of Brownsville on Tuesday. The GFS model, on the other hand, does not strengthen the ridge as much, and takes the system into South Texas Tuesday. Both of these solutions may be too fast, as some of the other computer models indicate that the system may linger near the Yucatan Peninsula for five or more days.


Figure 1. BAMM and GFDL track forecasts.

Southeast U.S.
Several of the global computer models continue to forecast that a tropical storm may form near the Bahama Islands on Monday or Tuesday. Any system forming in this region would be forced westward or west-southwestward into the Southeast Coast by a strong ridge of high pressure building in. There is as yet no sign of this development occurring, but this is the same area Katrina and Rita formed, so extra attention should be focused on this area.

TD 19?
A concentrated area of thunderstorms about 600 miles west-southwest of the Cape Verde Islands has developed a spin. There is some evidence of spiral banding and upper-level outflow channels beginning to form, and this disturbance could very well become Tropical Depression 19 and Tropical Storm Stan in the next day or two. The system is expected to move slowly northwest for the next five days and not threaten any land areas.

Hawaii
Hawaii is watching Tropical Depression Kenneth, which is dissipating as it approaches the Big Island. The remnants of Kenneth may bring heavy rains and the threat of flash flooding to the islands Saturday.

Baja
The Baja Peninsula is watching Hurricane Otis, which may strike the central Baja Peninsula on Sunday. Otis is taking a path very close to the Baja coast, where a narrow tongue of warm water will enable him to maintain hurricane intensity at a much further north point than most East Pacific hurricanes are able to. A hurricane watch has been issued for much of the Baja Peninsula.

Otis's remnants are a good bet to bring heavy rains and flooding to Arizona and northern Mexico early next week.

China
Super Typhoon Langwang, a small but intense typhoon with 150 mph sustained winds, is headed towards China and may hit northern Taiwan as a Category 4 storm on Sunday. Longwang is expected to gradually weaken but still hit mainland China on Monday as a Category 3 storm.

Jeff Masters

Updated: 2:02 PM GMT on September 30, 2005

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Hurricane Hunters find no depression

By: JeffMasters, 7:37 PM GMT on September 29, 2005

The Hurricane center released this special advisory at 3 pm EDT today:

"Data from an Air Force Reserve unit reconnaissance aircraft investigating the area of disturbed weather located between the Cayman Islands and Honduras indicate that the system remains disorganized and that a tropical depression has not formed. A large area of light and variable winds with a minimum pressure of 1009 mb...Or 29.80 inches... was detected about 170 miles southwest of Grand Cayman island. However... there is no thunderstorm activity collocated with the area of lowest pressure."

So, we will have to wait another day to see if this system will make up its mind whether or not it wants to be Stan the Man or Mr. Wimpy Tropical Blob. I still believe it will form into a tropical depression, but it's looking dicey for it to be anything more than a depression by the time it encounters the Yucatan Peninsula on Saturday. Once Stan/Mr. Wimpy Tropical Blob crosses the Yucatan, it may have new wind shear and dry air to overcome. If the system does manage to develop, the Mexican Gulf Coast or Texas look like the most likely targets.


Figure 1. The BAMM and GFDL models take the Caribbean disturbance into the Yucatan Peninsula. These models initialiazed the system about 100 miles too far to the southwest with their 2 pm and 8 am runs, respectively.

Southeast U.S.
Several of the global computer models have been persistently forecasting for the past three days that a tropical storm may form in the waters east of the Carolinas or Florida early next week. Any system forming in this region would be forced westward or west-southwestward into the Southeast Coast by a strong ridge of high pressure building in. There is as yet no sign of this development occurring, but we should watch the waters off of the Southeast coast this weekend for development.

Africa westward
The ITCZ is active in the region extending from the African coast westwards for 1000 miles. There is a concentrated area of thunderstorms 600 miles west-southwest of the Cape Verde Islands that may slowly develop into a tropical depression over the next few days as it drifts northward.

Hawaii
Hawaii is watching Tropical Storm Kenneth, which is expected to pass though the Islands Friday and Saturday as a tropical depression, and may bring heavy rains and the threat of flash flooding to the islands. Tropical depressions that have passed though the islands in previous years have caused serious flooding problems.

Baja
The Baja Peninsula is watching newly-formed Tropical Tropical Storm Otis, which may strike the central Baja Peninsula on Sunday. Otis is also a threat to bring heavy rains and flooding to Arizona and northern Mexico early next week.

China
Super Typhoon Langwang, a small but intense typhoon with 150 mph sustained winds, is headed towards China and may hit northern Taiwan as a Category 4 storm on Sunday. Longwang is expected to gradually weaken but still hit mainland China on Monday as a Category 3 storm.

Jeff Masters

Updated: 11:26 PM GMT on September 29, 2005

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Caribbean disturbance struggling again

By: JeffMasters, 2:21 PM GMT on September 29, 2005

Once again, the tropical disturbance in the western Caribbean sea southwest of Jamaica has fallen on hard times. It's refreshing for a change to see a system that doesn't develop when conditions seem to favor devlopment; this is typical behavior in most hurricane seasons, but certainly has been lacking in the Hurricane Season of 2005! The disturbance's deep convection has decreased considerably since last night, despite warm water beneath the system and somewhat favorable wind shear overhead. Wind shear remains in the 5 - 10 knot range, and has not decreased as forecast. Upper level outflow is poor, and the upper-level anticyclone overhead that was observed yesterday has grown weaker. The reconnaissance flight scheduled for this morning was moved to this afternoon, and they are currently investigating the system. There is some increased thunderstorm activity building on the southwest side of the disturbance this morning, and we may see a reapeat of yesterday, when the disturbance got better organized through the day, only to fall apart at night.

None of the computer forecast models develop the system, although they do still forecast a more favorable upper-level wind pattern to develop Friday and Saturday. However, the disturbance is approaching the Yucatan Peninsula, and development will probably be hampered by passage over the Peninsula. Dry air being pulled off of the Yucatan may also be a problem. The disturbance is unlikely to develop into anything more than a minimal tropical storm through Saturday. It may have a better chance for development once it enters the Gulf of Mexico early next week, although this is not assured--wind shear and more dry air may be problems for it.


Figure 1. The BAMM model takes the Caribbean disturbance into the Yucatan Peninsula. The GFDL model disippates the system immediately.

Southeast U.S.
Several of the global computer models have been persistently forecasting for the past three days that a tropical storm may form in the waters east of the Carolinas or Florida early next week. Any system forming in this region would be forced westward or west-southwestward into the Southeast Coast by a strong ridge of high pressure building in. There is as yet no sign of this development occurring, but we should watch the waters off of the Southeast coast the next few days.

Africa westward
The ITCZ is active in the region extending from the African coast westwards for 1000 miles. There are currently no suspect areas to focus on.

Hawaii
Hawaii is watching Tropical Storm Kenneth, which is expected to pass though the Islands Friday and Saturday as a tropical depression, and may bring heavy rains and the threat of flash flooding to the islands. Tropical depressions that have passed though the islands in previous years have caused serious flooding problems.

Baja
The Baja Peninsula is watching newly-formed Tropical Tropical Storm Otis, which may strike the central Baja Peninsula on Sunday. Otis is also a threat to bring heavy rains and flooding to Arizona and northern Mexico early next week.

China
Super Typhoon Langwang, a small but intense typhoon with 150 mph sustained winds, is headed towards China and may hit northern Taiwan as a Category 4 storm on Sunday. Longwang is expected to gradually weaken but still hit mainland China on Monday as a Category 3 storm.

Jeff Masters

Updated: 4:46 PM GMT on September 29, 2005

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Caribbean disturbance strengthening

By: JeffMasters, 8:02 PM GMT on September 28, 2005

The tropical disturbance in the western Caribbean sea, southwest of Jamaica, is now strengthening. The amount of deep convection has increased considerably since this morning, and this system now appears well on its way to becoming Tropical Depression 19 by tomorrow. A reconnaissance airplane is scheduled to visit the area Thursday morning at 8 am EDT.

Wind shear over the disturbance remains in the 5 - 10 knot range, which is in the slightly to moderately favorable range for tropical storm development. This wind shear is forecast to decrease the next two days. Upper level outflow channels have opened to the northeast and southwest, and a small upper-level anticyclone is over the system, helping ventilate the air pushed to the upper atmosphere by the strong updrafts in the storm's deep convection.

The disturbance is moving at about 13 mph to the west-northwest. This motion is forecast to slow down over the next few days, which will keep the system in the western Caribbean through Friday night. None of the computer forecast models develop the system, so their tracks of the disturbance are dubious. The GFS model takes the disturbance across western Cuba on Saturday. The BAMM model takes the system across the Yucatan Peninsula and into the southwest Gulf of Mexico. This seems more reasonable, given the strong ridge of high pressure developing over the Gulf of Mexico.


Figure 1. Early run of the BAMM model takes the Caribbean disturbance into the Yucatan Peninsula. The GFDL model disippates the system immediately.

Africa westward
The ITCZ is active in the region extending from the African coast westwards for 1000 miles. Some of the global computer models are forecasting that a tropical storm will develop along this area later this week. There are currently no suspect areas to focus on, though.

Hawaii and Baja
Hawaii is watching Tropical Storm Kenneth, which is expected to pass though the Islands Friday and Saturday. Kenneth should only be a tropical depression by then, but may bring heavy rains and the threat of flash flooding to the islands. Tropical depressions that have passed though the islands in previous years have caused serious flooding problems.

The Baja Peninsula is watching newly-formed Tropical Depression 15E, which may threaten the Baja Peninsula as a tropical storm by Sunday.

Jeff Masters

Updated: 8:04 PM GMT on September 28, 2005

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Caribbean disturbance struggling

By: JeffMasters, 1:02 PM GMT on September 28, 2005

The tropical disturbance in the central Caribbean sea, south of Jamaica, is struggling this morning. The amount of deep convection has decreased considerably since yesterday afternoon, and appears in small irregular patches around the weak circulation center. A reconnaissance airplane was scheduled to visit the area today but was cancelled. However, the convection has made a bit of a comeback since 2am EDT when there was almost none. The environment for development still seems fair to good. Wind shear over the disturbance remains in the 5 - 10 knot range, which is in the slightly to moderately favorable range for tropical storm development. This wind shear is forecast to decrease the next two days, and I still expect we will see this system become Tropical Depression 19 by Friday.

The disturbance has speeded up its forward motion to about 13 mph to the west-northwest. This motion is forecast to slow down over the next few days, which will keep the system in the western Caribbean through Friday night. The BAMM and GFS models both forecast that the system will then cross the Yucatan Peninsula and enter the southwest Gulf of Mexico. This seems reasonable, given the strong ridge of high pressure developing over the Gulf of Mexico.


Figure 1. Early run of the BAMM model takes the Caribbean disturbance into the Yucatan Peninsula. The GFDL model didn't do too well--it takes the disturbance the wrong way!

Africa westward
The ITCZ is active in the region extending from the African coast westwards for 1000 miles. Some of the global computer models are forecasting that a tropical storm will develop along this area later this week. There are currently no suspect areas to focus on, though.

Hawaii and Baja
Hawaii is watching Tropical Storm Kenneth, which is expected to pass though the Islands Friday and Saturday. Kenneth should only be a tropical depression by then, but may bring heavy rains and the threat of flash flooding to the islands. Tropical depressions that have passed though the islands in previous years have caused serious flooding problems.

The Baja Peninsula is watching newly-formed Tropical Depression 15E, which may threaten the Baja Peninsula as a tropical storm by Sunday.

Jeff Masters

Updated: 5:46 PM GMT on September 28, 2005

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Caribbean disturbance develops a spin

By: JeffMasters, 5:28 PM GMT on September 27, 2005

The tropical disturbance in the central Caribbean sea, south of Jamiaca, is still small and has limited deep convection, but now has a well-defined circulation visible on satellite imagery. Winds measured at NOAA buoy 42058 located at 15N 85W also showed this circulation, as the winds at the buoy switched from east to west this morning when the disturbance passed by. Surface pressures did not falling significantly at the buoy when the disturbance passed by, so this is still a very weak low pressure area. Wind shear over the disturbance has fallen to the 5 - 10 knot range, which is in the slightly to moderately favorable range for tropical storm development. An upper-level anti-cyclone appears to be developing on top of the disturbance, which should greatly aid the upper-level outflow needed to take away all the air lifted to the upper atmosphere by the deep convection near the storm's center.

The disturbance has slowed its forward motion to about 10 mph to the west-northwest. This motion is forecast to slow down even further over the next three days, which will keep the system in the western Caribbean through Friday, and favor development. The reconnaissance airplane scheduled to visit the area today was cancelled, and has been rescheduled for Wednesday.

The upper-level wind shear is forecast to relax further during the next two days, and I expect this system to become Tropical Depression 19 on Wednesday--Thursday at the latest. The global computer models do not develop this system into a tropical storm, and are not much help in forecasting what will happen. The latest 12Z (8am EDT) run of the GFS model predicts that the system will move to a point just south of the western tip of Cuba on Friday, but dissipates the system after that.


Figure 1. Early run of the BAMM model takes the Caribbean disturbance into the Yucatan Peninsula.

Africa westward
The ITCZ is active in the region extending from the African coast westwards for 1000 miles. Some of the global computer models are forecasting that a tropical storm will develop along this area later this week. There are currently no suspect areas to focus on, though.

Gulf of Mexico
A cluster of thunderstorms associated with the tail end of the cold front that pulled Rita northeast across the U.S. is over the northern Gulf of Mexico. Strong upper levels winds are producing 30 knots of shear over this region and should prevent any development.

Alaska and Hawaii
We don't talk much about these states in my tropical blog, but Nome, Alaska had a huge mid-latitude cyclone hit them Friday. The storm brought sustained tropical storm force winds gusting to 52 mph, a 10-foot storm surge, and a pressure of 972 mb! This was in essence a Category 1 hurricane, as far as the storm surge and pressure go. Thanks to wunderphotographer Destiny, who brought this newspaper article to my attention.

Hawaii has its second tropical system of the season to be concerned with. Hawaii dodged major Hurricane Jova last week, andTropical Storm Kenneth is expected to pass within 100 miles of the Islands by the end of the week. Kenneth should only be a tropical depression by then, and bring a few extra rain showers to the islands.

Jeff Masters

Updated: 6:00 PM GMT on September 27, 2005

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Caribbean disturbance still unimpressive

By: JeffMasters, 1:12 PM GMT on September 27, 2005

The tropical disturbance in the central Caribbean sea, south of Jamiaca, is still small and disorganized, and will not become a tropical depression today. The reconnaissance airplane scheduled to visit the area today will probably be cancelled. The disturbance has no surface circulation, surface pressures are not falling significantly, and there is about 10 knots of shear over it--which is marginal for tropical storm development. However, the largest burst of deep convection we've seen yet with this system began at about 4am EDT this morning, and the disturbance now has an expanding area of thunderstorms with cold tops that may signify the beginnings of an attempt to organize into a tropical depression. The disturbance has slowed its forward motion to about 10 mph to the west-northwest. This motion is forecast to slow down even further over the next three days, which will keep the system in the western Caribbean through Friday, and favor development.

I expect that we won't see a depression until late Wednesday, when the upper-level wind shear is forecast to relax significantly. I still give this disturbance a 70% chance of becoming a tropical storm by Friday, when it should be in the western Caribbean near Cuba or the Yucatan Peninsula. The global computer models do not develop this system into a tropical storm, and are not much help in forecasting what will happen. The GFS model predicts that the system will cross the Yucatan Peninsula into the southwest Gulf of Mexico early next week, but this forecast is too far in the future to give much credence to.


Figure 1. Early run of the BAMM model takes the Caribbean disturbance into the Yucatan Peninsula. It appears that the BAMM model got initialized with the disturbance too far to the south, so the projected track shown here is probably too far to the south.

Africa westward
The ITCZ is active in the region extending from the African coast westwards for 1000 miles. Some of the global computer models are forecasting that a tropical storm will develop along this area later this week.

Gulf of Mexico
A cluster of thunderstorms accosiated with the tail end of the cold front that pulled Rita northeast across the U.S. is over the northern Gulf of Mexico. Strong upper levels winds are producing 30 knots of shear over this region and should prevent any development for at least the next two days.

Alaska and Hawaii
We don't talk much about these states in my tropical blog, but Nome, Alaska had a huge mid-latitude cyclone hit them Friday. The storm brought sustained tropical storm force winds gusting to 52 mph, a 10-foot storm surge, and a pressure of 972 mb! This was in essence a Category 1 hurricane, as far as the storm surge and pressure go. Thanks to wunderphotographer Destiny, who brought this newspaper article to my attention.

Hawaii has its second tropical system of the season to be concerned with. Hawaii dodged major Hurricane Jova last week, andTropical Storm Kenneth is expected to pass within 100 miles of the Islands by the end of the week. Kenneth should only be a tropical depression by then, and bring a few extra rain showers to the islands.

Jeff Masters

Updated: 3:18 PM GMT on September 27, 2005

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No change to Caribbean disturbance

By: JeffMasters, 12:05 AM GMT on September 27, 2005

The tropical disturbance in the central Caribbean sea, south of Hispanolia, has changed little this afternoon, and remains very disorganized. There is no surface circulation, and pressures are not falling significantly. This disturbance split in two this morning, and the leading (westernmost) portion was effectively destroyed by wind shear associated with an upper level low to its northwest. The trailing (eastern) portion of the disturbance south of Hisponolia has about 10 knots of shear over it, which is marginal for tropical storm development.

The upper level low is moving to the north away from the disturbance, and a favorable low-shear environment is forecast to set up over the disturbance by Wednesday or Thursday. A reconnaissance airplane is scheduled to visit the area on Tuesday, but I doubt it will be needed until Wednesday. I still give this disturbance a 60% chance of becoming a tropical storm by Friday, when it should be near western Cuba or in the Gulf of Mexico. It is far too early to even offer even an educated guess about what might happen then.



Mid-Atlantic disturbance
A tropical disturbance located about 1000 miles east of the Lesser Antilles has effectively been destroyed by wind shear imparted by a large upper-level low pressure system to its west. Development of this disturbance is not expected. The ITCZ is very active in the region extending from the African coast westwards for 1000 miles. Tropical storm development along this area is possible later this week.

Elsewhere in the tropics
A cluster of thunderstorms accosiated with the tail end of the cold front that pulled Rita northeast across the U.S. is now emerging over the northern Gulf of Mexico, near the Florida Panhandle. Strong upper levels winds should prevent any development in this area for at least the next two days.

Alaska and Hawaii
We don't talk much about these states in my tropical blog, but Nome, Alaska had a huge mid-latitude cyclone hit them Friday. The storm brought sustained tropical storm force winds gusting to 52 mph, a 10-foot storm surge, and a pressure of 972 mb! This was in essence a Category 1 hurricane, as far as the storm surge and pressure go. Thanks to wunderphotographer Destiny, who brought this newspaper article to my attention.

Hawaii has its second tropical system of the season to be concerned with. Hawaii dodged major Hurricane Jova last week, andTropical Storm Kenneth is expected to pass within 100 miles of the Islands by the end of the week. Kenneth should only be a tropical depression by then, and bring a few extra rain showers to the islands.

Jeff Masters

Updated: 12:10 AM GMT on September 27, 2005

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Caribbean disturbance splits in two

By: JeffMasters, 4:56 PM GMT on September 26, 2005

Caribbean tropical disturbance
The main area of concern today is a tropical disturbance in the central Caribbean sea, south of Hispanolia. This disturbance has now split in two, which should slow down its development. Wind shear values have increased this morning over the leading (western) portion of the disturbance, and are now about 10 knots, which is only marginally favorable for a tropical depression to form. The trailing (eastern) portion of the disturbance south of Puerto Rico has less shear (5 - 10 knots) over it, and this portion of the disturbance is showing the greatest growth in deep convection this afternoon. This portion of the disturbance has the best chance of development. The shear is forecast to remain constant or decrease over the next 48 hours as the disturbance tracks west-northwest at 15 mph. While surface pressures have started to fall, there are currently no signs of a surface circulation, and the disturbance is still relatively small and disorganized. A reconnaissance airplane is scheduled to visit the area on Tuesday, if necessary.

An upper-level low pressure system over Cuba is forecast to weaken and move northwards during the next three days, which would lessen the shear over the disturbance and steer it more to the northwest, as seen in the early track model forecast from the BAMM model, shown below. The latest 12Z (8am EDT) run of the GFS model takes the disturbance across western Cuba and into the Gulf of Mexico by Saturday. These model results are not reliable, given that the disturbance has split in two and that this was not anticipated by the models.

I give this disturbance a 60% chance of becoming a tropical storm by Friday.



Mid-Atlantic disturbance
A tropical disturbance located about 1200 miles east of the Lesser Antilles remains poorly organized, and is suffering from wind shear imparted by a large upper-level low pressure system to its west. Development of this disturbance is not expected for the next two days.

Elsewhere in the tropics
A cluster of thunderstorms accosiated with the tail end of the cold front that pulled Rita northeast across the U.S. is now emerging over the northern Gulf of Mexico, near the Florida panhandle. Strong upper levels winds should prevent any development in this area for the next two days.

Long range models show the possibility of tropical storm development off the coast of Africa during the week, as well as the Caribbean. We still have about three weeks remaining of the peak period of hurricane season, and I expect two or three more tropical storms will form between now and mid-October.

Rita
I mentioned in my blog yesterday how Port Arthur got a direct hit by the eye or Rita, but escaped catastropic storm surge damage. The image below, constructed by NOAA's Hurricane Research Division based on data taken by the NOAA hurricane hunter aircraft, confirms that this occurred because the east eyewall of Rita with its powerful southerly winds never blew over the bay Port Arthur lies on. Thus, water from the open ocean was not forced up into the bay by the eyewall's winds. The maximum storm surge hit a very sparsely populated area of the Southwest Louisiana coast. The small town of Cameron (population 2000) was the largest town along this stretch of coast, and suffered damage similar to what was seen in Mississippi from Hurricane Katrina. The winds of the east side of the eyewall made landfall due south of Lake Charles, pushing the worst storm surge up to that city.


Figure 2. Winds of Rita at landfall as measured by the Stepped Frequency Microwave Radiometer (SFMR) instrument on the NOAA hurricane hunter aircraft.

Jeff Masters

Updated: 5:35 PM GMT on September 26, 2005

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Caribbean disturbance slowly developing

By: JeffMasters, 1:37 PM GMT on September 26, 2005

Caribbean tropical disturbance
The main area of concern today is a tropical disturbance in the Caribbean sea, south of Hispanolia. Surface pressures have started to fall in association with this disturbance, and deep convection has slowly increased the past 12 hours. Wind shear values have increased this morning over the leading (western) portion of the disturbance, and are now about 10 knots, which is only marginally favorable for a tropical depression to form. The trailing (eastern) portion of the disturbance south of Puerto Rico has less shear (5 - 10 knots) over it, and this portion of the disturbance is showing the greatest growth in deep convection this afternoon. The shear is forecast to to remain constant or decrease over the next 48 hours as the disturbance tracks west-northwest at 15 mph. There are currently no signs of a surface circulation, and the disturbance is still relatively small and disorganized, so it is not expected to develop into a tropical depression today. A reconnaissance airplane is scheduled to visit the area on Tuesday.

An upper-level low pressure system over Cuba is forecast to weaken and move northwards during the next three days, which would lessen the shear over the disturbance and steer it more to the northwest, as seen in the early track model forecast from the BAMM model, shown below. I give this disturbance a 60% chance of becoming a tropical storm by Thursday. However, the upper level winds are far from ideal for a tropical storm, and this system may struggle to survive if it does manage to form.



Mid-Atlantic disturbance
A tropical disturbance located about 1200 miles east of the Lesser Antilles remains poorly organized, and is suffering from wind shear imparted by a large upper-level low pressure system to its west. Development of this disturbance is not expected for the next two days.

Elsewhere in the tropics
Long range models show the possibility of more tropical development off the coast of Africa during the week, as well as the Caribbean and Gulf of Mexico. We still have about three weeks remaining of the peak period of hurricane season, and I expect two or three more tropical storms will form between now and mid-October.

Rita
I mentioned in my blog yesterday how Port Arthur got a direct hit by the eye or Rita, but escaped catastropic storm surge damage. The image below, constructed by NOAA's Hurricane Research Division based on data taken by the NOAA hurricane hunter aircraft, confirms that this occurred because the east eyewall of Rita with its powerful southerly winds never blew over the bay Port Arthur lies on. Thus, water from the open ocean was not forced up into the bay by the eyewall's winds. The maximum storm surge hit a very sparsely populated area of the Southwest Louisiana coast. The small town of Cameron (population 2000) was the largest town along this stretch of coast, and suffered damage similar to what was seen in Mississippi from Hurricane Katrina. The winds of the east side of the eyewall made landfall due south of Lake Charles, pushing the worst storm surge up to that city.


Figure 2. Winds of Rita at landfall as measured by the Stepped Frequency Microwave Radiometer (SFMR) instrument on the NOAA hurricane hunter aircraft.

Jeff Masters

Updated: 4:02 PM GMT on September 26, 2005

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Caribbean disturbance to watch, and Rita moves out

By: JeffMasters, 4:25 PM GMT on September 25, 2005

Rita
Rita is moving quickly to the northeast at 20 mph, confounding the model predictions of a stall and serious rainwater flooding disaster. The maximum rainfall from Rita--a swath of 8 - 12 inches--fell along a narrow strip from Port Arthur to Shreveport. While some rivers in the area are in flood stage, only 1 - 3 more inches of rain are expected to fall over the area, alleviating concerns of a second major flooding disaster on top of the serious storm surge flooding that occurred. The remains of Rita are moving too quickly to present a serious flooding problem for any addional regions along its path. A few isolated areas of 3 or 4 inches are the maximum amounts expected.

Port Arthur got a direct hit by the eye or Rita, but escaped catastropic storm surge damage. This occurred because the east eyewall of Rita with its powerful southerly winds never blew over the bay Port Arthur lies on, but passed over land just to the east of the city. Thus, water from the open ocean was not forced up into the bay by the eyewall's winds. The maximum storm surge hit a very sparsely populated area of the Southwest Louisiana coast. The small town of Cameron (population 2000) was the largest town along this stretch of coast, and apparently suffered damage similar to what was seen in Mississippi from Hurricane Katrina. Damage estimates for Rita (insured plus uninsured property) range from $5 - $10 billion. These numbers would have been in the $20 - $40 billion range had Rita hit Galveston/Houston. So, while Rita was very bad for the regions it did hit, we were lucky it wasn't far worse.

Caribbean tropical disturbance
The main area of concern today is a tropical disturbance in the southeastern Caribbean sea, due south of Puerto Rico. This disturbance has a small but growing area of deep convection associated with it, and is in an area of 10 knots of shear. This shear is forecast to decrease the next 48 hours, possibly allowing more substantial development as the disturbance tracks westward at 15 mph.

African activity
A tropical disturbance about 800 miles west-southwest
of the Cape Verde Islands remains poorly organized, and is suffering from wind shear imparted by a large upper-level low pressure system to its west. This shear is expected to decrease over the next two days, which may allow some development to occur. The disturbance is moving west-northwest, and will probably recurve to the norhteast in the middle of the Atlantic Ocean.

Long range models show the possibility of more tropical development off the coast of Africa during the week, as well. However, keep in mind that we are now into the last week of September, and it is rare for tropical storms that form in the eastern Atlantic this late in the season to affect any land areas. These late September storms nearly always recurve out to sea before threatening any land areas. This occurs because the jet stream is getting more active as Fall begins to assert itself, driving strong troughs of low pressure futher south where they can more easily recurve tropical systems to the north.

The place to watch this week is the Caribbean.

Jeff Masters

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Tropical Depression Rita still nasty

By: JeffMasters, 3:20 AM GMT on September 25, 2005

Rita continues to push inland, and is now creating flooding problems in Arkansas, Texas, and Louisiana. Radar estimates of rain indicate that over a foot of rain has fallen in some areas. Expect an additional 3 - 6 inches of rain per day to fall during the next three days along Rita's path. Fortunately, Rita is no longer expected to stall, and the regions most likely to be affected are under moderate to extreme drought conditions. Major flooding is already occurring on some rivers, but it will take a long time for many other rivers to come up to flood stage. The Mississippi is over 30 feet below flood stage in some places. Flash flooding along creeks and street flooding from excessive rains will be a problem everywhere, however. The storm surge flooding near the coast will steadily receed tonight, as the winds at the coast return to normal.


Figure 1.Drought conditions exist over most of the areas affected by Hurricane Rita.



Figure 2. Estimated rainfall from Rita.

Elsewhere in the tropics
A large non-tropical low pressure system near Bermuda has changed little the past day, but has the potential to develop into a tropical depression by Monday or Tuesday. This system is now moving quickly to the northeast, and is not a threat to any land areas.

A tropical disturbance near 11N 35W, off the coast of Africa, has gotten sheared by strong winds from a upper-level low pressure system to its east. Development of this disturbance is not likey until Tuesday at the earliest, and it is more likely that the shear will completely tear the disturbance apart before then.

Jeff Masters

Updated: 3:24 AM GMT on September 25, 2005

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Rita pushing inland

By: JeffMasters, 5:51 PM GMT on September 24, 2005

Rita continues to push inland, and is now a tropical storm. Many of the reporting stations failed during the height of the storm, so, as usual for a landfalling hurricane, we have little wind data. At the height of the storm, Port Arthur reported winds of 91 mph, gusting to 116. Beaumont had winds of 64 mph, gusting to 104. Houston had winds of 40 mph, gusting to 56, and New Orleans reported wind gusts as high as 40 mph.

Radar estimates of rain indicate that over a foot of rain has fallen in some areas. Expect an additional 6 - 8 inches of rain per day to fall during the next three days along Rita's path, with up to 25 inches falling in isolated areas. Fortunately, the regions most likely to be affected are under moderate to extreme drought conditions. Major flooding is already occurring on some rivers, but it will take a long time for many other rivers to come up to flood stage. The Mississippi is over 30 feet below flood stage in some places. Flash flooding along creeks and street flooding from excessive rains will be a problem everywhere, however. In addition, storm surge flooding was severe in Southwest Louisiana, and the surge penetrated over 40 miles inland in some areas. Exact storm surge height information is still unavailable. The surge will be slow to retreat, due to the strong onshore winds still affecting the coast.


Figure 1.Drought conditions exist over most of the areas affected by Hurricane Rita.



Figure 2. Estimated rainfall from Rita.

Where will Rita go?
Most of the latest model runs show Rita making a anti-cyclonic loop over northeastern Texas and central Louisiana, then perhaps heading back south to punish the landfall area five days from now. She may even move back over the waters of the Gulf. She would no longer be a tropical cyclone at that point, and redevelopment is not expected.

Elsewhere in the tropics
A large non-tropical low pressure system near Bermuda has changed little the past day, but has the potential to develop into a tropical depression by Monday or Tuesday. This system is expected to move little. A well-organized tropical disturbance near 11N 33W, off the coast of Africa, has a surface circulation and some deep convection. This system has the potential for development the next few days as it moves westward over the mid-Atlantic. High wind shear of 20 knots will keep the system from developing today. Long range models indicate that this disturbance will likely recurve to the northeast when it reaches the mid-Atlantic Ocean.

Jeff Masters

Updated: 7:19 PM GMT on September 24, 2005

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Rita making landfall as a weak Category 3

By: JeffMasters, 3:51 AM GMT on September 24, 2005

Rita is making landfall near Port Arthur, TX, as a weak Category 3 hurricane with 115 mph winds. There is nothing weak at all about any major hurricane, and it definitely a bad night to be holed up in your house or shelter listening to the awesome destruction unleased by this powerful hurricane. Radar shows some very intense echoes in the northern eyewall smashing into the coast, and infrared satellite imagery confirms the presence of extremely cold cloud tops in the northern eyewall. It appears that the interaction of the eyewall with land is producing extra surface convergence of winds that is forcing up some strong updrafts, creating very high thunderstorm tops.

Where will Rita go?
Most of the latest model runs show Rita making a anti-cyclonic loop over northeastern Texas and central Louisiana, then perhaps heading back south to punish the landfall area five days from now. She may even move back over the waters of the Gulf. She would no longer be a tropical cyclone at that point, and redevelopment is not expected.

Elsewhere in the tropics
Tropical Depression Philippe has being absorbed into a large non-tropical low pressure system near Bermuda. This system is expected to move little the next three days, and may develop into a tropical depression. A well-organized tropical disturbance near 11N 33W, off the coast of Africa, has a surface circulation and some deep convection. This system has the potential for development the next few days as it moves westward over the mid-Atlantic. Long range models indicate that this disturbance will likely recurve to the northeast when it reaches the mid-Atlantic Ocean.

Jeff Masters

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Rita making landfall as a weak Catgeory 3

By: JeffMasters, 9:07 PM GMT on September 23, 2005

Rita is making landfall near Port Arthur, TX, as a weak Category 3 hurricane with 115 mph winds. There is nothing weak at all about any major hurricane, and it definitely a bad night to be holed up in your house or shelter listening to the awesome destruction unleased by this powerful hurricane. Radar shows some very intense echoes in the northern eyewall smashing into the coast, and infrared satellite imagery confirms the presence of extremely cold cloud tops in the northern eyewall. It appears that the interaction of the eyewall with land is producing extra surface convergence of winds that is forcing up some strong updrafts, creating very high thunderstorm tops.

Where will Rita go?
Most of the latest model runs show Rita making a anti-cyclonic loop over northeastern Texas and central Louisiana, then perhaps heading back south to punish the landfall area five days from now. She may even move back over the waters of the Gulf. She would no longer be a tropical cyclone at that point, and redevelopment is not expected.

Elsewhere in the tropics
Tropical Depression Philippe has being absorbed into a large non-tropical low pressure system near Bermuda. This system is expected to move little the next three days, and may develop into a tropical depression. A well-organized tropical disturbance near 11N 33W, off the coast of Africa, has a surface circulation and some deep convection. This system has the potential for development the next few days as it moves westward over the mid-Atlantic. Long range models indicate that this disturbance will likely recurve to the northeast when it reaches the mid-Atlantic Ocean.

Jeff Masters

Updated: 3:50 AM GMT on September 24, 2005

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Rita maintaining Cat 4 status

By: JeffMasters, 1:51 PM GMT on September 23, 2005

Rita completed an eyewall replacement cycle this morning. The inner eyewall completely collapsed, and an outer eyewall 35 miles in diameter took its place. During the time, the pressure rose to 927 mb, and remained constant at that level between 4:30 am and 8 am EDT. The hurricane hunters noted no increase in surface winds, which remained at about 140 mph. They did note that the eyewall was beginning to contract again, which may signal the beginning of an intensification cycle. Rita is over warm waters (30C) which are warm to a great depth. Thus, the amount of heat available for intensification is high (see plot below). By this afternoon, Rita will be passing over waters that are still warm, but are shallow, so the amount of heat available to draw energy from is much lower. This should end any intensification. In addition, 10 - 15 knots of shear is impacting Rita's south side, and one can see from satellite images the lack of high cirrus clouds on her south side that results from this shear. This shear is expected to increase to 25 knots by Saturday morning, and the combined effect of the shear and the lower heat content of the ocean beneath her should prevent her from making landfall any stronger than she is now (Category 4), and may act to weaken her to a Category 3 hurricane.



Figure 1. Heat potential of the waters beneath Rita show that she will soon be passing to an area of lower available heat (dark blue area). This should put an end to any intensification cycle she may be starting on.

Although Rita should be a Category 3 or 4 hurricane at landfall, she will still carry to the coast a storm surge characteristic of a much stronger hurricane. A Category 4 or 5 level storm surge is likely along a 40 - 60 miles stretch of coast near and to the right of where the storm makes landfall on Saturday. Storm surge heights will peak at 15 - 20 feet in some bays, and bring the ocean inland up to 50 miles from the coast. This surge will be lower and cover less length of coastline than Katrina's surge, but will still cause widespread destruction in the cities of Port Arthur, Orange, and Cameron.



We can track Rita now from the Lake Charles radar. This radar will probably get knocked out by Rita sometime Saturday.

Where will Rita go?
The latest computer models are tightly clustered around a landfall point just west of the Texas/Louisiana border. Confidence is high in this forecast. Houston and Galveston should escape major wind and storm surge damage, and only experience maximum sustained winds of 60 mph with gusts to 85 mph. It is still too early to tell what will happen after landfall, as the models all take Rita different ways. A major rainwater flooding problem will ensue after Rita's landfall, with 10 - 30 inches of rain falling over a large area of Texas and Louisiana.

Elsewhere in the tropics
Tropical Storm Philippe is a minimal tropical storm that may bring 30 mph winds to Bermuda, but is expected to die by Saturday. A strong tropical disturbance near 11N 30W, off the coast of Africa, has acquired a circulation and some deep convection. This system has the potential for development the next few days as it moves west to west-northwest over the Atlantic. Another area of disturbed weather 500 miles south of Bermuda also needs to be watched. Long range computer models do not show a threat to land from either of these systems in the next five days.

Jeff Masters

Updated: 3:24 PM GMT on September 23, 2005

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Rita still holding steady

By: JeffMasters, 3:25 AM GMT on September 23, 2005

There are no major changes to report tonight on Rita's situation. The pressure continues to hold steady in the 913 - 917 mb range, which is very low, considering she is going through a long eyewall replacement cycle. The hurricane force winds have expanded out to 80 miles, which is still quite a bit less than Katrina's 120 miles. I expect that the area of extreme storm surge from Rita will be less than Katrina's, since Rita is a smaller storm.

Rita's eyewall replacement cycle is almost complete, and we may see some slight strengthening Friday morning. By Friday evening, slight to moderate weakening may occur until landfall Saturday. This will occur as a result of 10 knots of shear on her south side from an upper-level high pressure system, and from passage over ocean waters with less heat content. By landfall time on Saturday afternoon, I still expect that Rita will be a Category 3 or 4 hurricane, but still carry to the coast a storm surge characteristic of a much stronger hurricane. A Category 4 or 5 level storm surge is likely along a 40 - 60 miles stretch of coast to the right of where the storm makes landfall on Saturday. Storm surge heights will peak at 15 - 20 feet in some bays, and bring the ocean inland up to 50 miles from the coast. Large sections of I-10 between Houston and Beaumont could be inundated, and the flood waters may reach the cities of Beaumont, Orange, and Lake Charles.


Figure 1. Expected inland penetration of a Category 5 level hurricane storm surge. Only areas along and to the right of Rita's landfall point may get a Category 5 storm surge. If Rita makes landfall east of Galveston, Houston and Galveston will not see the storm surge flooding shown here.

Current buoy measurements
NOAA buoy 42001 in Rita's western eyewall measured sustained winds of 90 mph, gusting to 112 mph, and 34 foot waves at 2:50 pm CDT. A time series plot of the wind and pressure from buoy 42001 is worth checking out. Winds are starting to fall now as Rita moves away. The buoy did not quite make it into the eye of the strongest part of the eyewall.

Where will Rita go?
The 18Z (2pm EDT) computer models are more tightly clustered than before, focusing on a point just west of the Texas/Louisiana border. It is still too early to tell what will happen after landfall, as the models all take Rita different ways. It is heartening to see that the GFS model is no longer taking Rita back out to sea and hitting Brownsville! Regardless, it appears that a major rainwater flooding disaster will ensue after Rita's landfall, with 10 - 30 inches of rain falling over a large area.

Elsewhere in the tropics
Tropical Storm Philippe is a minimal tropical storm heading out to sea, and is not a threat to any land areas. The ITCZ is growing more active tonight, and there may be an area of development to watch in the mid-Atlantic by tomorrow.

Updated: 3:26 AM GMT on September 23, 2005

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Rita levels off at Cat 4 intensity

By: JeffMasters, 8:29 PM GMT on September 22, 2005

Reconnaissance flights this afternoon indicate that the weakening phase Rita went through has ceased. Her central presure has held steady between 913 and 915 mb between noon and 4 pm, and the surface winds are steady at about 145 - 150 mph. Rita is a strong Category 4 hurricane. She appears to be going through a collapse of the inner eyewall, which the hurricane hunters have noted has a large gap in it. It may take 12 - 24 hours for Rita to rebuild her eyewall. During that time, some fluctuations in strength may occur, but weakening is most likely. This would occur as a result of 10 knots of shear on her south side from an upper-level high pressure system, and from passage over ocean waters with less heat content. By landfall time on Saturday afternoon, it is expected that Rita will be a Category 3 or 4 hurricane, but still carry to the coast a storm surge characteristic of a much stronger hurricane. A Category 4 or 5 level storm surge is likely along a 60 - 80 miles stretch of coast to the right of where the storm makes landfall on Saturday. Storm surge heights will peak at 15 - 20 feet in some bays, and bring the ocean inland up to 50 miles from the coast. Large sections of I-10 between Houston and Beaumont could be inundated, and the flood waters may reach the cities of Beaumont, Orange, and Lake Charles.


Figure 1. Expected inland penetration of a Category 5 level hurricane storm surge. Only areas along and to the right of Rita's landfall point may get a Category 5 storm surge. If Rita makes landfall east of Galveston, Houston and Galveston will not see the storm surge flooding shown here.

Current buoy measurements
NOAA buoy 42001 in Rita's western eyewall measured sustained winds of 90 mph, gusting to 112 mph, and 34 foot waves at 2:50 pm CDT. A time series plot of the wind and pressure from buoy 42001 is worth checking out.

Where will Rita go?
The 12Z (8am EDT) computer models in general show a shift a bit more to the east, making a landfall near the Texas/Louisiana border more likely. Keep in mind that the average error in landfall location for a 48 hour forecast is 125 miles, which means the landfall point could be anywhere from the Central Texas coast near Matagorda to the central Louisiana coast near New Iberia.

The models runs are now pretty much agreed that steering currents will weaken and Rita will stall and drift westward or southwestward once it moves inland. This will result in severe flooding problems for wherever Rita stalls, as 10 - 30 inches of rain could fall in the affected region. As is usually the case when steering currents get weak, the model forecasts of Rita's motion are highly unreliable. Rita may stall over the notheast Texas, or western or central Louisiana. Oklahoma and Arkansas are looking less likely. It's too early to tell with much reliability. It may not be until next Wednesday when the remnants of Rita finally are gone.

Elsewhere in the tropics
Tropical Storm Philippe is a minimal tropical storm heading out to sea, and is not a threat to any land areas. An area of disturbed weather off of the coast of Honduras has diminished and is no longer a threat. Development off of the coast of Africa is possible beginning on Sunday.

A new blog called TheDiscussionBlog has been set up by tornadoty to serve as an alternate discussion forum for those who want to pose questions. I will read it and respond to questions there if I get the time, which hasn't been too plentiful of late, unfortunately.
Jeff Masters

Updated: 8:45 PM GMT on September 22, 2005

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Rita's eyewall collapsing soon

By: JeffMasters, 3:44 PM GMT on September 22, 2005

We continue to live history as this incredible Hurricane Season of 2005 unfolds more stunning surprises. Rita has peaked in intensity as the third strongest hurricane of all time, with a pressure of 897 mb and 175 mph winds. She is on the decline now, as the 11am hurricane hunter mission found a pressure of 913 mb, and increase of 5 mb in just 3 hours. The hurricane hunters also found concentric eyewalls of 17 and 55 nautical miles in diameter. All these signs indicate that Rita will continue to weaken today as her inner eyewall collapses and an eyewall replacement cycle begins. Rita is about to leave the vicinity of a warm eddy of Gulf water called the Loop Current that has been aiding her intensification. In addition, 10 knots of shear has developed on her south side, thanks to the fact that the upper-level high pressure system that was providing such excellent outflow for Rita has now shifted to the southeast of the storm. All these signs point to a substantial weakening trend for Rita that will continue through Friday and probably reduce her to a Category 4 hurricane. The GFDL forecast model and NHC predict that this weakening trend will continue until landfall Saturday, when Rita will be a Category 3 hurricane. Lower heat content water and continued shear are expected to cause this weakening.

While this is cause for some relief, Rita, like Katrina did, will still bring to the coast a storm surge characteristic of a much stronger hurricane. A Category 4 or 5 level storm surge is likely along a 60 - 80 miles stretch of coast to the right of where the storm makes landfall on Saturday. Storm surge heights will peak at 15 - 20 feet in some bays, and bring the ocean inland up to 50 miles from the coast. Large sections of I-10 between Houston and Beaumont could be inundated, and the flood waters may reach the cities of Beaumont, Orange, and Lake Charles. Wind damage will be severe, and Houston can expect a hazardous rain of glass from its high rise building like was experienced during Hurricane Alica in 1983. If the eye passes just west of Galveston Bay, the storm surge will push 1 - 3 of water into some of Houston's eastern suburbs, such as Deer Park.


Figure 1. Expected inland penetration of a Category 5 level hurricane storm surge. Only areas along and to the right of Rita's landfall point may get a Category 5 storm surge. If Rita makes landfall east of Galveston, Houston and Galveston will not see the storm surge flooding shown here.

Current buoy measurements
NOAA buoy 42001 measured sustained winds of 58 mph, gusting to 78 mph, and 34 foot waves at 10am CDT. At the time, the buoy was located 75 miles WNW of Rita. This evening at 5pm CDT, Rita should make a very close pass by this buoy. I expect waves of 50 - 70 feet will impact the buoy, and huge swells from Rita are already starting to pound the Gulf Coast. A time series plot of the wind and pressure from buoy 42001 is worth checking out.

Where will Rita go?
The computer models made a modest shift eastwards this morning, calling for a landfall between Galveston and the Texas/Louisiana border. The Hurricane Center shifted their landfall point as well, and now go with the model consensus. The models have been flip-flopping frequently, and it is not unreasonable to suppose that they will shift the landfall point 50 or so miles further west again this tonight. However, a landfall within 100 miles of Galveston seems to be the the best call. Landfall will still occur sometime Saturday, but this may be afternoon instead of morning, as the storm is moving slower than before.

Most of the models now indicate that steering currents will weaken and Rita will stall and sit in place for several days once it moves inland. This will result in severe flooding problems for wherever Rita stalls, as 10 - 30 inches of rain could fall in the affected region. As is usually the case when steering current get weak, the model forecasts of Rita's motion are highly unreliable. Rita may stall over the Dallas area, or central Louisiana, or Oklahoma or Arkansas. It's too early to tell. Finally, on Tuesday, Rita's remnants are forecast to lift out to the north.

Elsewhere in the tropics
Tropical Storm Philippe is a minimal tropical storm heading out to sea, and is not a threat to any land areas. An area of disturbed weather off of the coast of Honduras is being sheared by the strong upper-level winds flowing south from Hurricane Rita. If this disturbed area still exists on Sunday, it has some potential for development. Development off of the coast of Africa is also possible beginning on Sunday.

Jeff Masters

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Rita weakening, but still catastrophic

By: JeffMasters, 1:53 PM GMT on September 22, 2005

We continue to live history as this incredible Hurricane Season of 2005 unfolds more stunning surprises. Rita has peaked in intensity as the third strongest hurricane of all time, with a pressure of 897 mb and 175 mph winds. She is on the decline now, as the 7:30 am hurricane hunter mission found a pressure of "only" 907 mb and winds 5 mph weaker. The hurricane hunters also found evidence of a concentric eyewall forming outside of the main inner eyewall, and the inner eyewall had begun to take on an elliptical shape. All these signs indicate that Rita will continue to weaken today as her inner eyewall collapses and an eyewall replacement cycle begins. Additionally, Rita is about to leave the vicinity of a warm eddy of Gulf water called the Loop Current that has been aiding her intensification. Also, 10 knots of shear has developed on her south side, thanks to the fact that the upper-level high pressure system that was providing such excellent outflow for Rita has now shifted to the southeast of the storm. All these signs point to a substantial weakening trend for Rita that will continue through Friday and probably reduce her to a Category 4 hurricane. The GFDL forecast model predicts that this weakening trend will continue until landfall Saturday, when Rita will be a Category 3 hurricane.

While this is cause for some relief, Rita, like her weaker sister Katrina did, will still bring a Category 5 level storm surge along a 60 - 80 miles stretch of coast to the right of where the storm makes landfall on Saturday. Storm surge heights will peak at 20 - 25 feet in some bays, and bring the ocean inland up to 50 miles from the coast. Large sections of I-10 between Houston and Beaumont will be inundated, and the flood waters will reach the cities of Beaumont, Orange, and Lake Charles. Wind damage will be severe, and Houston can expect a hazardous rain of glass from its high rise building like was experienced during Hurricane Alica in 1983. If the eye passes just west of Galveston Bay, the storm surge will push 1 - 3 of water into some of Houston's eastern suburbs, such as Deer Park.

Current buoy measurements
NOAA buoy 42001 measured sustained winds of 52 mph, gusting to 64 mph, and 31 foot waves at 8am CDT. At the time, the buoy was located 80 miles WNW of Rita. This evening at 5pm CDT, Rita should make a very close pass by this buoy. I expect waves of 50 - 70 feet will impact the buoy, and huge swells from Rita are already starting to pound the Gulf Coast. A time series plot of the wind and pressure from buoy 42001 is worth checking out.

Where will Rita go?
The computer models made a modest shift eastwards this morning, calling for a landfall between Galveston and the Texas/Louisiana border. The Hurricane Center shifted their landfall point as well, but not as far as the model consensus. The models have been flip-flopping frequently, and it is not unreasonable to suppose that they will shift the landfall point 50 or so miles further west again this afternoon. However, a landfall within 100 miles of Galveston seems to be the the best call. Landfall will still occur sometime Saturday, but this may be afternoon instead of morning, as the storm is moving slower than before.

Most of the models now indicate that steering currents will weaken and Rita will stall and sit in place for several days once it moves inland. This will result in severe flooding problems for wherever Rita stalls, as 10 - 30 inches of rain could fall in the affected region. As is usually the case when steering current get weak, the model forecasts of Rita's motion are highly unreliable. Rita may stall over the Dallas area, or central Louisiana, or Oklahoma or Arkansas. It's too early to tell. Finally, on Tuesday, Rita's remnants are forecast to lift out to the north.

Elsewhere in the tropics
Tropical Storm Philippe is a minimal tropical storm heading out to sea, and is not a threat to any land areas. An area of disturbed weather off of the coast of Honduras is being sheared by the strong upper-level winds flowing south from Hurricane Rita. If this disturbed area still exists on Sunday, it has some potential for development. Development off of the coast of Africa is also possible beginning on Sunday.

I'll post a storm surge forecast map at about 10:30 EDT, and more updates today as needed.

Jeff Masters

Updated: 2:32 PM GMT on September 22, 2005

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Rita may stall over Texas

By: JeffMasters, 12:54 AM GMT on September 22, 2005

The latest runs of two key computer models, the GFS and GFDL, now indicate that the trough of low pressure that was expected to pick up Rita and pull her rapidly northward through Texas will not be strong enough to do so. Instead, these models forecast that Rita will make landfall near Galveston, penetrate inland between 50 and 200 miles, then slowly drift southwestward for nearly two days, as a high pressure ridge will build in to her north. Finally, a second trough is forecast to lift Rita out of Texas on Tuesday. If this scenario develops, not only will the coast receive catastrophic damage from the storm surge, but interior Texas, including the Dallas/Fort Worth area, might see a deluge of 15 - 30 inches of rain. A huge portion of Texas would be a disaster area. We'll have to wait for the next set of model runs due out by tomorrow morning to know better.

The 7:09 pm eye report from the hurricane hunters found a 897 mb pressure and flight level winds of 161 knots (186 mph). This pressure makes Rita the 3rd strongest Atlantic hurricane of all time. Tonight, Rita will be passing over the Loop Current, a warm eddy of water in the Gulf that aided Katrina's growth to a Category 5 hurricane. Fueled by this pool of deep warm water and an almost ideal upper level wind environment, Rita should continue to intensify until Thursday morning, when she will pass beyond the Loop Current. The eye has shrunk to 20 nm diameter from 25 nm earlier this afternoon. By the time the eye shrinks down to 10 nm, the eyewall will collapse and an eyewall replacement cycle begin, putting an end to this intensification cycle. With potentially another 12 hours to go before this happens, Rita could challenge Gilbert's 888 mb pressure record.

The list of strongest hurricanes of all time now reads:

Hurricane Gilbert (888 mb, 1988)

The Great Labor Day Hurricane (892 mb, 1935)

Hurricane Rita (897 mb, 2005)

Hurricane Allen (899 mb, 1980)

Hurricane Katrina (902 mb, 2005)

Hurricane Camille (905 mb, 1969)

How low can Rita go?

Jeff Masters

Updated: 3:01 AM GMT on September 22, 2005

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Rita: 3rd strongest hurricane ever

By: JeffMasters, 12:08 AM GMT on September 22, 2005

The 7:09 pm eye report from the hurricane hunters found a 904 mb pressure and flight level winds of 161 knots (186 mph). This pressure makes Rita the 3rd strongest Atlantic hurricane of all time. Tonight, Rita will be passing over the Loop Current, a warm eddy of water in the Gulf that aided Katrina's growth to a Category 5 hurricane. Fueled by this pool of deep warm water and an almost ideal upper level wind environment, Rita should continue to intensify until Thursday morning, when she will pass beyond the Loop Current. The eye has shrunk to 20 nm diameter from 25 nm earlier this afternoon. By the time the eye shrinks down to 10 nm, the eyewall will collapse and an eyewall replacement cycle begin, putting an end to this intensification cycle. With potentially another 12 hours to go before this happens, Rita could challenge Gilbert's 888 mb pressure record.

The list of strongest hurricanes of all time now reads:

Hurricane Gilbert (888 mb, 1988)

The Great Labor Day Hurricane (892 mb, 1935)

Hurricane Rita (898 mb, 2005)

Hurricane Allen (899 mb, 1980)

Hurricane Katrina (902 mb, 2005)

Hurricane Camille (905 mb, 1969)

I expect to rewrite this list when the next reconnaissance aircraft reaches Rita about 9pm tonight. How low can Rita go?

Jeff Masters

Updated: 12:23 AM GMT on September 22, 2005

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Rita: Category 5, still intensifying

By: JeffMasters, 5:42 PM GMT on September 21, 2005

The 3:37 pm eye report from the hurricane hunters found a 914 mb pressure and flight level winds of 161 knots (186 mph). These numbers plus the satellite intensity estimates support upgrading Rita to a Category 5 hurricane. Tonight, Rita will be passing over the Loop Current, a warm eddy of water in the Gulf that aided Katrina's growth to a Category 5 hurricane. Fueled by this pool of deep warm water and an almost ideal upper level wind environment, Rita should continue to intensify until Thursday morning, when she will pass beyond the Loop Current. The eye has started to shrink as Rita continues to intensify, and is down to 20 nm diameter from 25 nm earlier this afternoon. By the time the eye shrinks down to 10 nm, the eyewall will collapse and an eyewall replacement cycle begin, putting an end to this intensification cycle. With another 12 hours to go before this happens, Rita could approach historic intensity, and is already one of the ten strongest Atlantic hurricanes on record.

The list of strongest hurricanes of all time reads:

Hurricane Gilbert (888 mb, 1988)

The Great Labor Day Hurricane (892 mb, 1935)

Hurricane Allen (899 mb, 1980)

Hurricane Katrina (902 mb, 2005)

Hurricane Camille (905 mb, 1969)

How low will Rita go?

I'll post the rest of my discussion from this morning below:


It's been a long time since Texas had a severe hurricane. Hurricane Bret hit the state in 1999 as a Category 4 hurricane, but was small and hit the relatively unpopulated Padre Island National Seashore. Bret gave Texas the unique distinction of being the only state to get hit by a Category 4 hurricane that didn't get its name retired. In 1988, Hurricane Gilbert, the strongest hurricane of all time, just missed Texas, hitting south of the border. The last hurricane to do serious damage to Texas was Hurricane Alica of 1983, which hit Galveston as a weak Category 3 storm, pushing a 10 - 12 foot storm surge into Galveston Bay. Alica killed 21 people, and its $2 billion price tag was the highest in Texas hurricane history.

Texas's luck is about to change. Rita, looking more and more like a nightmare copy of Katrina somehow displaced in time, will make sure of that. The forecast models we so heavily rely on did not anticipate another Katrina-like storm when Rita first formed and plowed through the Florida Straits. But now, the forecasts mirror the reality unfolding today in the Gulf of Mexico. Rita will be another huge destructive hurricane for the Gulf Coast. This time, it is Texas's turn. Every other state on the Gulf Coast has borne the burden of the immense destruction created by our unprecedented onslaught of intense hurricanes the past two hurricane seasons. No state will be left out.

Rita's impact on the Florida Keys
The residents of the Keys returning to their homes today are the lucky ones, for the Keys escaped serious damage. A 4 - 6 foot storm surge did hit the Lower Keys and flood the Coastal Highway, but this quickly subsided and the highway is now open to traffic again. Some minor to moderate wind damage occurred, but winds in Marathon only reached 38 mph, gusting to 53 mph, while the winds at Key West Airport reached 56 mph, gusting to 73 mph. There was an unofficial report of sustained winds of 75 mph gusting to 102 mph in Key West. Rainfall amounts of up to 12 inches occurred in the Keys, causing minor flooding problems.


Figure 1. Estimated rainfall from Hurricane Rita.


Figure 2. Wind and pressure plot from a coastal weather station in the Lower Keys. Note how the pressure after Rita's passage remains lower than that before her passage--Rita has depressed pressure values over an area hundreds of miles wide.

Rita now
Rita's presentation on satellite imagery is classic; she has a well-formed eye, large Central Dense Overcast (CDO) of cirrus clouds surrounding the eye, and well developed outflow on all sides, particularly to the north. Rita is currently smaller than Katrina, though. Katrina at her peak had hurricane force winds that extended outward 120 miles from the center; Rita's hurricane force winds only extend out 70 miles from the center. This will change as Rita continues to intensify and expand in size over the next day or two. There is little shear over Rita at present, nor is there expected to be the next three days. Water temperatures are 1 - 2C cooler over the central Gulf than they were for Katrina, which may keep Rita from attaining quite the intensity Katrina did. However, once Rita crosses the Gulf and arrives in the western Gulf on Friday, water temperatures warm back up to 30 - 31C, about the same temperatures as the waters Katrina had to work with.

Rita at landfall
Rita's future intensity will largely be controlled by impossible-to-predict eyewall replacement cycles. Rita is growing large enough that she is creating her own upper level environment that will be relatively impervious to any external shearing winds that try to weaken her. I expect Rita to be a Category 4 hurricane at landfall.

The landfall location forecast has increased in confidence since yesterday, as the computer models have started to converge on a landfall location on the middle Texas coast. Western Louisiana still needs to be concerned, as does Corpus Christi, but New Orleans should escape Rita with nothing more than some fairly ordinary thunderstorms in some of the outermost spiral bands. A significant storm surge capable of flooding New Orleans is very unlikely.

A very significant storm surge is expected along and to the right of where Rita makes landfall on the Texas coast. Surge heights may reach 25 feet or higher, breaking the record 22 foot storm surge seen in 1961 during the Category 4 Hurricane Carla.

Elsewhere in the tropics
Tropical Storm Philippe continues northward away from land, and is not not expected to be a threat. Strong shearing winds will likely tear Philippe apart by Saturday. The remainder of the tropics are quiet and expected to remain so through Friday. By Saturday, the chances of tropical storm development off the coast of Africa begin to increase.

Jeff Masters

Updated: 9:20 PM GMT on September 21, 2005

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Rita: another Katrina?

By: JeffMasters, 2:23 PM GMT on September 21, 2005

It's been a long time since Texas had a severe hurricane. Hurricane Bret hit the state in 1999 as a Category 4 hurricane, but was small and hit the relatively unpopulated Padre Island National Seashore. Bret gave Texas the unique distinction of being the only state to get hit by a Category 4 hurricane that didn't get its name retired. In 1988, Hurricane Gilbert, the strongest hurricane of all time, just missed Texas, hitting south of the border. The last hurricane to do serious damage to Texas was Hurricane Alica of 1983, which hit Galveston as a weak Category 3 storm, pushing a 10 - 12 foot storm surge into Galveston Bay. Alica killed 21 people, and its $2 billion price tag was the highest in Texas hurricane history.

Texas's luck is about to change. Rita, looking more and more like a nightmare copy of Katrina somehow displaced in time, will make sure of that. The forecast models we so heavily rely on did not anticipate another Katrina-like storm when Rita first formed and plowed through the Florida Straits. But now, the forecasts mirror the reality unfolding today in the Gulf of Mexico. Rita will be another huge destructive hurricane for the Gulf Coast. This time, it is Texas's turn. Every other state on the Gulf Coast has borne the burden of the immense destruction created by our unprecedented onslaught of intense hurricanes the past two hurricane seasons. No state will be left out.

Rita's impact on the Florida Keys
The residents of the Keys returning to their homes today are the lucky ones, for the Keys escaped serious damage. A 4 - 6 foot storm surge did hit the Lower Keys and flood the Coastal Highway, but this quickly subsided and the highway is now open to traffic again. Some minor to moderate wind damage occurred, but winds in Marathon only reached 38 mph, gusting to 53 mph, while the winds at Key West Airport reached 56 mph, gusting to 73 mph. There was an unofficial report of sustained winds of 75 mph gusting to 102 mph in Key West. Rainfall amounts of up to 12 inches occurred in the Keys, causing minor flooding problems.


Figure 1. Estimated rainfall from Hurricane Rita.


Figure 2. Wind and pressure plot from a coastal weather station in the Lower Keys. Note how the pressure after Rita's passage remains lower than that before her passage--Rita has depressed pressure values over an area hundreds of miles wide.

Rita now
Rita's presentation on satellite imagery is classic; she has a well-formed eye, large Central Dense Overcast (CDO) of cirrus clouds surrounding the eye, and well developed outflow on all sides, particularly to the north. This is the look of a solid, intensifying Category 4 hurricane. Intensification will continue until the eye shrinks to 10 miles or so in diameter and grows unstable, when the eyewall will collapse and an eyewall replacement cycle will begin. This may take another 24 hours or so, at which point Rita could be a Category 5 hurricane. Rita is currently smaller than Katrina, though. Katrina at her peak had hurricane force winds that extended outward 120 miles from the center; Rita's hurricane force winds only extend out 45 miles from the center. This will change as Rita continues to intensify and expand in size over the next day or two. There is little shear over Rita at present, nor is there expected to be the next three days. Water temperatures are 1 - 2C cooler over the central Gulf than they were for Katrina, which may keep Rita from attaining quite the intensity Katrina did. However, once Rita crosses the Gulf and arrives in the western Gulf on Friday, water temperatures warm back up to 30 - 31C, about the same temperatures as the waters Katrina had to work with. I doubt Rita will match Katrina's size or ferocity, but she might come to within 90% of the storm that Katrina was.

Rita at landfall
Rita's future intensity will largely be controlled by impossible-to-predict eyewall replacement cycles. Rita is growing large enough that she is creating her own upper level environment that will be relatively impervious to any external shearing winds that try to weaken her. I expect Rita to be a Category 4 hurricane at landfall.

The landfall location forecast has increased in confidence since yesterday, as the computer models have started to converge on a landfall location on the middle Texas coast. Western Louisiana still needs to be concerned, as does Corpus Christi, but New Orleans should escape Rita with nothing more than some fairly ordinary thunderstorms in some of the outermost spiral bands. A significant storm surge capable of flooding New Orleans is very unlikely.

A very significant storm surge is expected along and to the right of where Rita makes landfall on the Texas coast. Surge heights may reach 18 feet or higher, breaking the record 18.5 foot storm surge seen in 1961 during the Category 4 Hurricane Carla.

Elsewhere in the tropics
Tropical Storm Philippe continues northward away from land, and is not not expected to be a threat. Strong shearing winds will likely tear Philippe apart by Saturday. The remainder of the tropics are quiet and expected to remain so through Friday. By Saturday, the chances of tropical storm development off the coast of Africa begin to increase.

Jeff Masters

Updated: 2:25 PM GMT on September 21, 2005

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Key West's hurricane grotto works again

By: JeffMasters, 2:23 AM GMT on September 21, 2005

Tonight I don't want to think about what Rita is doing, or where she might go, or how strong she might be. I just want to be thankful for small miracles. In my blog entry for Sunday, I talked about the church in Key West called the St. Mary's Star of the Sea Roman Catholic Church. In 1922, a nun built a "hurricane grotto" on the grounds of the church in memory of the 600 who died during the great Atlantic-Gulf hurricane of Sept. 10, 1919, a Category 4 hurricane that made a direct hit on Key West. The nun vowed that as long as the grotto stood, Key West would not suffer the brunt of another hurricane. Well, the protection of the grotto worked again. Key West barely escaped the brunt of a severe hurricane that could have been so very much worse. Had Rita's intensification cycle started 24 hours earlier, and she tracked 50 miles further north, the city of Key West would have been devastated. The Key West airport never measured sustained hurricane force winds from Rita, although the National Hurricane Center did receive an unofficial report of sustained winds of 75 mph with gusts to 102 mph in the Key West area. There was flooding and wind damage that will no doubt add up to tens of millions of dollars, but Kest West is feeling lucky tonight. Key Westers, pay a visit to your grotto tomorrow and give thanks!

Jeff Masters

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Rita a Category 2 hurricane

By: JeffMasters, 4:54 PM GMT on September 20, 2005

Rita was upgraded to a hurricane this morning at 9:15 am, and is already a Category 2 hurricane after just four hours. The 4:00 pm EDT hurricane hunter mission found winds at 10,000 feet of 89 knots (102 mph), which corresponds to surface winds of 92 mph. The SFMR instrument on the NOAA hurricane hunter aircraft found surface winds of 100 mph, making Rita a Category 2 hurricane. The central pressure was 973 mb, down 12 mb in the past 9 hours. At this rate of intensification, Rita will be a Category 3 hurricane tomorrow. The Key West radar loop is most impressive the past three hours, showing a rapidly intensifying hurricane with strong spiral banding, and a solid eyewall forming.


Here are the peak wind gusts as of 4:30 pm EDT from Rita:

53 mph at Marathon Airport
60 mph at Key West International Airport
58 mph at Molasses Reef light
48 mph at Long Key light
78 mph at Sombrero Key light
92 mph at Sand Key light (60 mph sustained)
50 mph at Dry Tortugas light
65 mph at Fowey Rocks

The northern eyewall passed just south of the lower Keys and Key West between 1 pm and 3 pm today, sparing the lower Keys the brunt of the storm's fury. The Lower Keys escaped with sustained winds of 40 - 50 mph and gusts to 60 mph. A storm surge of 4 - 6 feet did accompany the arrival of the eyewall. The Florida Highway patrol has reported water and
wave action over the Overseas Highway in a number of areas. The Overseas Highway at 73.5 mile marker is impassable and has been barricaded to all traffic. It looks like Key West's hurricane grotto protected the city again! If Rita had tracked just 50 miles further north and started its intensification cycle 24 hours earlier, much of Key West might have been serioussly damaged with some loss of life.

Rita in the Gulf
As Rita continues on into the Gulf of Mexico tonight, continued strengthening is expected. The shear over her has dropped below 5 knots, and may decrease further. The upper level outflow has improved considerably today, and Rita now has a more circular and symmetric appearance with excellent outflow on all sides. The water under Rita will remain in the 30 - 31C range until Wednesday morning, then cool off to 29 - 30C over the middle of the Gulf of Mexico, where the cooler waters stirred up to the surface by Hurricane Katrina still remain. These cooler waters should keep Rita in the strong Category 2 to strong Category 3 range as she moves across the central Gulf. Once Rita approaches the coast of Texas, the cold water wake of Katrina ends and water temperatures warm up to about 30C, which may allow some intensification. Rita will be a Category 2, 3, or 4 hurricane by landfall in Texas on Saturday. The 8am of the GFS model indicates Rita may be a Category 4 at landfall.


Figure 2.Sea Surface temperatures for Monday, September 19. Note the cooler wake in the center of the Gulf left by Katrina.

Threat to Louisiana fades
Last night, the NOAA jet flew its first mission into Rita, and collected high-density data used to initialize last night's computer model runs. The models are more tightly clustered than before, and now all the models point to a landfall in Texas Saturday, somewhere between Brownsville and Galveston. NHC thinks that their current projected landfall point near Matagorda, TX is more reliable than usual. If we take the average NHC 4-day forecast track error of 200 miles and knock it down by 50 miles or so since we're assuming NHC is correct about their more reliable than usual forecast, this gives a probable landfall point somewhere between Corpus Christi and the Texas/Louisiana border. So, western Louisiana is still at considerable risk, but New Orleans will miss this hurricane.

Hurricane Philippe
Stong westerly winds have started to tear Philippe apart, and he is now a tropical storm. Philippe is not expected to affect any land areas, including Bermuda, as he heads north and then northeast, out to sea.

Wave between Africa and the Antilles
The large low pressure system halfway between Africa and the Antilles islands has been absorbed by Philippe and is no longer a threat. Later in the week, the shear over the central Atlantic is expected to decrease, and we could see another tropical storm form in this region.

Jeff Masters

Updated: 8:59 PM GMT on September 20, 2005

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Rita upgraded to hurricane

By: JeffMasters, 1:06 PM GMT on September 20, 2005

Rita was upgraded to a hurricane with a special 9:15 am advisory. The 9:15am EDT hurricane hunter mission found winds at 5000 feet of 78 knots (90 mph), which corresponds to surface winds of minimal hurricane force (74 mph).The central pressure was 982 mb, down 3 mb in the past 1 1/2 hours. The Key West radar loop is most impressive the past three hours, showing a transformation from a disorganized, elliptical system to a more circular storm with much more intense spiral banding. An large eye with a 35 mile diameter has formed, but is still organizing and has gaps. Infrared sateliite images now show a warm spot where the eye is forming.



Here are the peak wind gusts as of 11:00 am EDT from Rita:

53 mph at Marathon Airport
50 mph at Key West International Airport
58 mph at Molasses Reef light
48 mph at Long Key light
72 mph at Sombrero Key light
47 mph at Sand Key light
38 mph at Dry Tortugas light

Sustained tropical force winds of 40 mph or higher will spread over the entire Keys chain this morning, extending as far north as Miami. The eye of Rita is shrinking, and the northern eyewall will pass over or just south of the lower Keys and Key West between noon and 3 pm today. Sustained winds of 70 - 80 mph and gusts of 100 mph will accompany passage of the northern eyewall. If the eyewall misses to the south, the lower Keys will escape with sustained winds of 50 - 60 mph and gusts to 85 mph. A storm surge of 5 - 7 feet will accompany the arrival of the eyewall, flooding parts of the coastal highway and low-lying areas. Moderate roof damage and extensive damage to mobile homes is also expected in the lower Keys.

Rita in the Gulf
Once Rita emerges into the Gulf of Mexico this afternoon, continued strengthening is expected--but not explosive deepening. The center of the upper-level high that Rita needs to carry away all the air her eyewall convection is injecting into the upper atmosphere is located to the east of her, and thus the outflow over Rita is poor in some areas, particularly the south side. This situation is predicted to improve some and allow Rita to strengthen to a Category 3 hurricane by Thursday. Water temperatures over the middle of the Gulf of Mexico are 1 - 2C cooler than those near Key West, thanks to all the cold water stirred up by Katrina. This may keep Rita as a strong Category 2 hurricane. Once Rita approaches the coast of Texas, the cold water wake of Katrina ends and water temperatures warm up again, which may allow some more intensification. Rita is not expected to reach Category 4 status.


Figure 2.Sea Surface temperatures for Sunday, September 18. Note the cooler wake in the center of the Gulf left by Katrina.

Threat to Louisiana fades
Last night, the NOAA jet flew its first mission into Rita, and collected high-density data used to initialize last night's computer model runs. The models are more tightly clustered than before, and now all the models point to a landfall in Texas Saturday, somewhere between Brownsville and Galveston. She is expected to be a Category 2 or 3 at landfall. Western Louisiana is still at high risk, but New Orleans will miss this hurricane. However, if Rita makes landfall in western Louisiana, she may push 1 - 2 feet of storm surge into Lake Pontchartrain. This could cause problems with the weakened New Orleans levee system and possibly destroy the temporary patches that were installed, allowing the areas of the city that are starting to drain to flood once more.

Philippe
Philippe is slowly strengthening but heading northward out to sea. Philippe will continue to strengthen and head north, and is not expected to affect any land areas, including Bermuda.

Wave between Africa and the Antilles
A large low pressure system is halfway between Africa and the Antilles islands. While this system does have a surface circulation and considerable deep convection, 15-20 knots of upper-level wind shear will keep this system from developing into a tropical depression. Later in the week, the shear over the central Atlantic is expected to decrease, and we could see another tropical storm form in this region, but probably not from the current area of disturbed weather mentioned above.

Jeff Masters

Updated: 3:22 PM GMT on September 20, 2005

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Hurricane Rita

By: JeffMasters, 2:26 AM GMT on September 20, 2005

It's not official, but it soon will be--Rita is a hurricane. The latest satellite imagery shows a huge and expanding burst of deep convection with very cold cloud tops near the center. The latest UW-CIMSS satellite intensity estimate puts Rita as a 80 mph hurricane with a 982 mb central pressure. Radar imagery from Camaguey, Cuba shows a partially formed elliptical eyewall, open to the north. Long range Miami radar shows a large and expanding area of radar echoes approaching Florida. Tropical storm force winds have moved outward from 105 miles from the center at 5pm, to 120 miles at 11pm. Rita is a large, impressive Category 1 hurricane, and growing stronger and larger by the hour. The lower Keys are in for a nasty pounding. This may equal or exceed the most damaging hurricane ever in Key West, which I believe was Category 2 Hurricane Georges in 1998, which brought a 4 - 6 foot storm surge and Category 1 winds to the lower Keys, causing $340 million in damage. Expect roof and moderate structural damage to homes and businesses from Rita. Hundred of mobile homes will be damaged or destroyed. Large trees and power poles will be toppled. Damage will be at least $1 billion, which will largely be uninsured losses, since many insurance companies won't insure propery in the Keys.

Where will Rita hit?

Take your pick from today's latest model runs:

GFS: TX/LA border
NOGAPS: Brownsville, TX
UKMET: Galveston
GFDL: Galveston

So, the model trend that had taken Rita towards landfall in western Louisiana has now reversed, to Texas' detriment. Tune in tomorrow morning, the NOAA jet is flying its first mission in Rita, a high-altitude synoptic surveilance mission tonight that should greatly aid the model predictions that will be complete in the morning. I won't start believing the models until I see some runs with the NOAA jet data initializing them.

Jeff Masters

Updated: 2:48 AM GMT on September 20, 2005

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Key West: mandatory evacuation

By: JeffMasters, 4:35 PM GMT on September 19, 2005

There's a church in Key West called the St. Mary's Star of the Sea Roman Catholic Church. In 1922, a nun built a "hurricane grotto" on the grounds of the church in memory of the 600 who died during the great Atlantic-Gulf hurricane of Sept. 10, 1919, a Category 4 hurricane that made a direct hit on Key West. The nun vowed that as long as the grotto stood, Key West would not suffer the brunt of another hurricane. Key West residents regularly make pilgrimages to the grotto to pray for protection from hurricanes. And so far, the grotto has worked--no Key West resident has died from a hurricane strike since the 1919 hurricane. I've heard from at least one Key West resident that plans to pay a visit to the grotto today, which I think is a good idea. A little divine intervention is what is needed this Hurricane Season of 2005. The current model runs were apparently not initialized last night with the "grotto factor", since they all show Rita's path taking the storm over or very near Key West. Still, the average error in a 24 hour forecast has been about 60 miles the past 10 years, so Key West may yet miss the brunt of this hurricane.

And a hurricane it will be. Satellite images show that deep convection has now wrapped all the way around the west side of Rita and into the center, where a complete eyewall is starting to form. Spiral bands from the storm are already visible on Miami long-range radar as Rita moves towards Florida and expands in size. Winds at George Town in the Bahama Islands were 37 mph, gusting to 57 mph at noon today. The 12:15 satellite intensity estimate from the University of Wisconsin was 991 mb and 68 mph surface winds. There won't be another hurricane hunter aircraft in the storm until 2pm EDT today, but I think we can anticipate that they will find a continuation of the strengthening trend observed today. Rita will be a hurricane by early this evening, and probably a Category 2 hurricane tomorrow. A 6 - 9 foot storm surge can be expected near and 50 miles to the to the north of where Rita's eye passes, and a foot higher if she hits near high tide (11am Tuesday). The surge plus the wind damage will cause hundreds of millions in damage in the Keys, but should cause no major loss of life, since I'm sure after Katrina residents of low-lying areas under evacuation orders will be compelled to comply more readily than usual. Key West and all of the lower and middle Keys were given a mandatory evacuation order this morning. This is a bit of a risky call by the emergency managers; They'll never get everyone out in time, and risk having people stuck on the bridges when the storm hits. Still, they have a lot of experience evacuating the Keys the past seven years, so hopefully it will go smoothly.


Figure 1. Expected maximum storm surge from Rita.

Rita in the Gulf
Once Rita emerges into the Gulf of Mexico, continued strengthening is expected, and she will likely attain at least Category 3 status by Wednesday. However, water temperatures over the middle of the Gulf of Mexico are 1 - 2C cooler than those near Key West, thanks to all the cold water stirred up by Katrina. This cooler water should not allow Rita to grow as strong as Katrina (not a very bold statement, considering Katrina was the 4th strongest hurricane on record!) Rita will probably grow to a Category 3, and has a chance at Category 4 status if she passes over the Gulf Stream loop current, an eddy of very warm water south of New Orleans near 26N latitude.


Figure 2.Sea Surface temperatures for Sunday, September 18. Note the cooler wake in the center of the Gulf left by Katrina.


Figure 3.Ocean heat potential for Sunday, September 18. The big red spot south at 26N 89W shows where the Gulf Loop Current is, a very deep eddy of warm water that will enhance intensification of Rita if she passes over it.

Where will Rita hit?
Take your pick of today's models runs:

GFDL: Central Louisiana (Houma)
GFS: Western Louisiana (Lake Charles)
UKMET: Eastern Texas (Galveston)
NOGAPS: South Texas (Corpus Christi)

Each set of model runs has moved the track of Rita progressively further east. The official NHC forecast has been following along, but staying further back. What we've seen so far this hurricane season is that when the models start trending this way, that's where the storm eventually winds up going. So my best guess is that Rita will hit Louisiana Friday as a Category 3 hurricane. What's the average error for a 5-day forecast? 270 miles. So, everyone from the Florida Panhandle to the Mexican border is still at risk.

Philippe
Philippe is slowly strengthening but heading northward out to sea. Philippe will continue to strengthen and head north, and is now not expected to affect any land areas, including Bermuda.

Wave between Africa and the Antilles
A large low pressure system is halfway between Africa and the Antilles islands. While this system does have a surface circulation and considerable deep convection, 15 knots of upper-level wind shear will keep this system from developing into a tropical depression for at least the next two days.

Jeff Masters

Updated: 5:26 PM GMT on September 19, 2005

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Key West: brace for a strengthening Rita

By: JeffMasters, 11:17 AM GMT on September 19, 2005

Rita continues to slowly strengthen. The hurricane hunters have found a steady pressure fall of 2 mb between 3am and 6am EDT this morning, and an increase in winds at their flight level of 5000 feet from 57 to 64 knots. The latest penetration at 7:30am found a pressure of 997 mb and winds of 64 knots at flight level, the same levels as recorded at 6am, so Rita has not intensified in the past two hours.

However, the rate of intensification should quicken later today as the shear over Rita decreases, and Rita will likely be at least a strong Category 1 hurricane or Category 2 hurricane when it passes near Key West Tuesday morning. There is still a small chance Rita could intensify to a Category 3 hurricane when it passes the Keys. The Keys can handle a strong Category 2 hurricane without loss of life--barely. If I lived in the Keys I would stay put today, assuming I had a sturdy shelter to ride out the storm. A 6 - 8 foot storm surge--or a foot higher if Rita hits at high tide--is expected over Key West, and less further north. Even if Rita suddenly strengthens to a Category 3, the winds would not have time to build up a storm surge characteristic of a Cat 3 hurricane until after she passes the Keys. Wind damage would be severe over Key West, however. This all assumes Rita makes a direct hit on Key West. The latest track forecast takes her south of Key West 50 miles or so, sparing the city the winds of the eyewall, and Key West may escape with only light to moderate damage from Rita.



While the Keys are likely to escape with a hard but bearable hit from a strengthening Category 1 or 2 hurricane, the Gulf Coast will not be so lucky. There is nothing in the long-range forecast that I can see that will prevent Rita from intensifying into a Category 3 or stronger hurricane. The entire stretch of coast from 500 miles south of Brownsville, Texas to Mobile, Alabama is at risk--no one can say with any confidence where Rita will hit this far in advance. Texas and Louisiana are at the highest risk. The current model trend is to recurve Rita earlier and earlier, so residents from Corpus Christi to New Orleans need to be particulary concerned.

Philippe
As for Philippe--which is now a hurricane--we do not need to be concerned with him for at least five days, and probably never. The odds are over 95% that Phillipe will stay out to sea and not affect any land areas except Bermuda.

I'll have a more in-depth update by noon EDT today.

Jeff Masters

Updated: 1:49 PM GMT on September 19, 2005

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Keys residents: get out tonight, or wake up early Monday

By: JeffMasters, 3:48 AM GMT on September 19, 2005

Florida Keys residents should seriously consider evacuating tonight. If you decide not to, check on Rita's forecasted strength early Monday morning, after the 5am NHC advisory is out. Think about evacuating then.

After reading the 11pm NHC discussion, which reported that the 67 knot winds measured by the Hurricane Hunters was not representative of the general winds in Rita, I am a little less concerned that Rita will intensify to a major Category 3 hurricane as it passes through the Keys Monday night or Tuesday morning. Also, the cloud tops in Rita have warmed a bit in the past few hours, and it appears that Rita is taking a breather from her recent intensification burst.

Still, I don't like what I see. The hurricane hunters found a 40% complete eyewall has formed. The upper level outflow is excellent on the north side, and the storm is over warm 30 - 31C water. I'd give it a 5% chance that Rita will be a Category 3 hurricane passing through the Keys. If I lived in the Keys, I would think real hard about leaving, just in case that 5% chance verifies. The sudden intensification tonight happened the face of about 10 knots of shear, which one can see impacting the SW side of the storm on satellite imagery. If the shear goes to less than 5 knots, which is expected to happen by Tuesday, Rita will intensify very rapidly. Rita will probably be a Category 1 or 2 hurricane when it moves through the Keys Monday night. The Keys can handle a Category 2 hurricane--barely.

The Keys take a full 72 hours to evacuate, and now that New Orleans has been taken out by Katrina, the Keys represent the number one most vulnerable area in the U.S. for serious loss of life from a hurricane strike. Even though the evacuation order has already been given for visitors and tourists, not everyone will be able to make it out if Rita suddenly intensifies tomorrow to a Category 3 status.

The nighmare scenario is what happened during the Great Labor Day Hurricane of 1935, which intensified from a tropical storm with 70 mph winds to a Category 5 hurricane with 160 mph winds in just 42 hours as it approached the Keys. Over 400 Keys residents died in the ensuing disaster.

So, if you live in the Keys, get your bag packed. Wake up early tomorrow, and check out the 5am advisory. If Rita is a hurricane by then, consider hitting the road early. But if the roads are totally jammed, it's probably better to ride it out in a sturdy shelter rather than be caught on the 7-Mile Bridge in a hurricane.

While the Keys are likely to escape with a hard but bearable hit from a strengthening Category 1 or 2 hurricane, the Gulf Coast will not be so lucky. There is nothing in the long-range forecast that I can see that will prevent Rita from intensifying into a Category 3 or stronger hurricane. The entire stretch of coast from 500 miles south of Brownsville, Texas to New Orleans is at risk--no one can say with any confidence where Rita will hit this far in advance. Texas is at the highest risk, though, and needs to watch Rita the most carefully.

Philippe
As for Philippe--which is now a hurricane--we do not need to be concerned with him for at least five days, and probably never. The odds are over 90% that Phillipe will stay out to sea and not affect any land areas except Bermuda.

Jeff Masters

Updated: 4:19 AM GMT on September 19, 2005

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Keys residents: pack your bags

By: JeffMasters, 1:59 AM GMT on September 19, 2005

Florida Keys residents should seriously consider evacuating tonight. While Rita is still a modest tropical storm, I don't like what I see at all from the latest hurricane hunter report. They found a fairly high pressure, 1004 mb, but flight level winds at 5000 feet were already up to 67 knots-- hurricane force--and a 40% complete eyewall has formed. While the odds are considerably against Rita becoming a Category 3 hurricane by the time it moves through the Keys, it is certainly possible. I'd give it a 10% chance of happening, and if I lived in the Keys, I wouldn't risk staying for that 10% chance. The sudden intensification is happening in the face of about 5 - 10 knots of shear, which one can see impacting the SW side of the storm on satellite imagery. The outflow at upper levels is resricted there, but looking VERY impressive on the north side. Rita seems intent on becoming a Category 1 hurricane Monday, and will probably be a Category 1 or 2 hurricane when it moves through the Keys Monday night. The Keys can handle a Category 2 hurricane--barely.

The Keys take a full 72 hours to evacuate, and now that New Orleans has been taken out by Katrina, the Keys represent the number one most vulnerable area in the U.S. for serious loss of life from a hurricane strike. Even though the evacuation order has already been given for visitors and tourists, not everyone will be able to make it out if Rita suddenly intensifies tomorrow to a Category 3 status.

The nighmare scenario is what happened during the Great Labor Day Hurricane of 1935, which intensified from a tropical storm with 70 mph winds to a Category 5 hurricane with 160 mph winds in just 42 hours as it approached the Keys. Over 400 Keys residents died in the ensuing disaster.

So, if I lived in the Keys, I would start packing my bags now. Hurricane intensity forecasts are not reliable. I would wait until 11:00 tonight and see what the Hurricane Center has to say, and if they also don't like the looks of this storm, I'd hit the road. If you decide not to go, be sure to take another look very early tomorrow morning, after the 5am advisory comes out, and be ready to hit the road early in the morning. Better to be horribly inconvenienced than dead.

Jeff Masters

Updated: 2:11 AM GMT on September 19, 2005

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TD 18: the one to watch

By: JeffMasters, 3:15 PM GMT on September 18, 2005

The forecasters at the National Hurricane Center are pretty busy this weekend, writing advisories for two systems in the Atlantic and three in the eastern Pacific. Thankfully, Ophelia is finally gone, but we are watching another wave of the coast of Africa that might develop into a tropical depression. But for now, we can ignore all of these systems except one--Tropical Depression 18, which is expected to build into Tropical Storm Rita later today. The NHC agreed with this assessment last night, taking the unusual step of diverting a hurricane hunter airplane--the mission bound for Philippe was recalled and sent to TD 18 instead. The Florida Keys and Texas are at greatest risk from this developing storm.

Current status of TD 18
TD 18 is over the Turks and Caicos Islands, which one can think of at a western extension of the Bahama Islands. After an initial west-northwest motion last night, TD 18 has settled into a track 10 degrees north of due west which will take her through the Bahama Islands today and tomorrow, and threaten Cuba and the Florida Keys after that. TD 18 is devloping a little faster than Philippe did, and showing some solid deep convection over the center, good spiral banding on the northwest side, and some decent upper-level outflow on the north side. The shear over TD 18 has decreased steady the past 48 hours, and is now down to 5 - 10 knots, which should support some moderate intensification. This shear is expected to remain constant or decrease slightly over the next 24 hours. The upper-level winds look favorable--an upper-level anticyclone has developed on top and will provide favorable outflow. Water temperatures are very warm--30 to 31C. However, there are two factors which will probably prevent TD 18 from attaining hurricane status in the next three days:

1) An upper level low pressure system over Cuba and Jamaica. This upper low is positioned to the southwest of TD 18, and the counterclockwise flow of air around the upper low will bring 5 - 10 knots of shear to TD 18's southwest flank over the next few days. The upper low is forecast to move west and maintain it's position on the southwest side of TD 18. However, after three days, the low is forecast to weaken, which would generate the lower shear environment TD 18 would need to grow into a hurricane.

2) Interaction with Cuba and the Yucatan Peninsula. TD 18's current track may put it on top of Cuba Tuesday. One model, the UKMET, indicates TD 18 will cross Cuba and get tangled up with the Yucatan Peninsula. Interaction with either of both of these land areas will likely prevent TD 18 from attaining hurricane strength until it can clear them and get its entire ciculation into the Gulf of Mexico.

Track of TD 18
The strong ridge of high pressure steering TD 18 to the west is forecast to persist for the next five days. The computer models differ some on how strong this ridge will be after TD 18 clears the tip of the Yucatan Peninsula, with the UKMET and Canadian models taking the storm west-southwest into Mexico, the GFS and NOGAPS taking the storm towards south Texas, and the GFDL taking it into Louisiana. The strength of a trough of low pressure expected to swing across the Midwest U.S. late in the week will be crucial toward determining the where the storm ultimately makes landfall along the Gulf Coast. The strength of this trough is impossible to determine at this point. I believe that Texas is at greatest risk, judging by the current forecast guidance.

Intensity forecast for TD 18
Both of the major computer intensity forecast models, the SHIPS and GFDL models, make Rita a Category 1 hurricane by Wednesday, as it passes through the Florida Keys. It is unlikely TD 18 could intensify to a stronger than Category 1 hurricane before it hits the Keys, since it's current state of organization is relatively poor, and there will still be some shear of the southwest side affecting the storm the next two days.

Assuming the storm misses Cuba, there is nothing I can see to prevent Rita from becoming a major Category 3 or higher hurricane in the Gulf of Mexico by Friday. Shear is forecast to be light, and water temperatures are at record high levels. But if Rita hits Cuba or the Yucatan Peninsula, it will be difficult for her to regroup quickly enough to attain more than Category 2 hurricane strength.

Philippe
Tropical Storm Philippe continues to organize, and has all the appearance of a system on its way towards becoming a large a powerful major hurricane. Philippe's track looks good for everyone except the residents of Bermuda. I looked through the tracks of all hurricanes that passed close to the point where Philippe is forecast to be five days from now, a few hundred miles south of Bermuda. Only three hurricanes in the past one hundred years have gone on to hit the U.S. that passed through a location that far to the north and east. The longer range computer models do suggest Philippe may take a more westerly motion towards the U.S. late in the week, but the odds of a trough of low pressure picking up Philippe and recurving him out to sea are high. I seriously doubt Philippe will affect any land areas except perhaps Bermuda.

ITCZ disturbance
The Intertropical Convergence Zone (ITCZ), remains active. A tropical wave in the ITCZ located about 900 miles west-southwest of the Cape Verde Islands has acquired a low level circulation and some deep convection, and may grow into Tropical Depression 19 later in the week as it moves west-northwest over the open Atlantic Ocean.

Jeff Masters

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Double trouble: Phillippe and Rita

By: JeffMasters, 4:10 PM GMT on September 17, 2005

We are now in the third week of September, when water temperatures in the Atlantic are at their yearly peak and historically the strongest hurricanes develop. Given that this year's Atlantic water temperatures are the highest on record, we have in place the best fuel source ever seen for making intense hurricanes. Combined with the low levels of wind shear developing and forecast to remain low over the tropical Atlantic, we have a high potential for the formation of major and potentially destructive hurricanes. A newly formed tropical depression approaching the Windward Islands and a developing system north of the Dominican Republic both have the potential to develop into serious hurricanes, and will need to be watched closely this week.

TD 17 (Phillippe?)
TD 17 is here, and will likely be the first major hurricane of September. This storm will be with us for the next two weeks, since it is moving slowly and has a large area of ocean ahead of it. The storm is in a an environment favorable for intensification, and should be Tropical Storm Phillippe Sunday and Hurricane Phillippe by Tuesday. The shear over the storm is 10 knots, and forecast to decrease. The waters beneath it are a warm 30C (86F). Some impressive lowel-level spiral bands have formed. Upper level outflow is good on the southeast and north sides, and an upper-level anticyclone overhead should provide a very favorable ouflow environment for intensification. All indications are that Phillipe will be a hurricane, and probably a major hurricane.

Fortunately, initial computer model forecasts do not show this storm striking any land areas. A large trough in the mid-Atlantic is pulling TD 17 northwest, and the storm should pass east of the Lesser Antilles Islands. Tropical storm conditions may affect some of the northernmost islands, though. Once the storm moves north of the islands, long-range computer models indicate the possibility it will continue northwestwards and threaten Bermuda. However, remember how wrong these long-range forecast were for Ophelia, forecasting a landfall in Georgia early on! It is impossible to say where TD 17 may go five days from now.

Blob northeast of the Dominican Republic (Rita?)
A disturbance northeast of Puerto Rico continues to generate some impressive clusters of thunderstorms, and definitely has the look of a system organizing into a tropical depression. A mid and possibly low-level circulation has developed near 22N 69W, about 250 miles east of the Turks and Caicos Islands. The main convection is well east of this circulation center, and would have to build over the center before a tropical depression could form. There is about 10 knots of westerly shear over the disturbance, keeping the convection blown over to its east side. This shear is expected to decrease over the next 24 hours, which should allow TD 18 to form later today or tomorrow. The upper-level winds look favorable--an upper-level anticyclone has developed on top, and should provide good outflow for the storm once more deep convection establishes itself. Shear is expected to remain low, water temperatures are very warm--30 to 31C. The chances for this system to become Tropical Storm Rita--and possibly Hurricane Rita--are high.

This system is expected to move west-northwestward through the Bahama Islands and towards South Florida the next few days. Several of the long-range computer models have been consistently forecasting that a strong ridge of high pressure will build across Florida about five days from now, forcing the system on a more westerly or even west-southwesterly path across Cuba towards Mexico's Yucatan Peninsula.


Figure 1. Early track model forecasts for the Puerto Rico blob.

ITCZ
The Intertropical Convergence Zone (ITCZ), remains active. However, the main activity is at about 8N latitude, which is probably too far south to generate a tropical cyclone. If some of this activity works its way to 9N or 10N, we may have a better chance of development. Most of the global computer models indicate that a new tropical storm will form from the ITCZ sometime during the next week.

Ophelia
There is some good news in the tropics today--Ophelia is weakening rapidly, and has given Massachusetts a wide enough berth so that tropical storm conditions will not occur there. Nova Scotia, though, will likely get a direct hit from Ophelia and receive 45 mph winds, 1 - 3 inches of rain, and a 1 - 3 foot storm surge.

Damage estimates from Ophelia's long unwelcome stay over North Carolina are said to be less than $800 million--a remarkably high figure for what was only a tropical storm for all but a two square miles area of the state. Perhaps the category system for ranking hurricanes also needs to take into account how slow a storm moves. What we really need is a separate "storm damage potential" category for hurricanes, as Steve Gregory has championed on his blog.

For those of you who missed by blog last night, there was a scientific first accomplished in Ophelia last night--the first ever remotely-piloted aircraft penetration of a tropical cyclone. A aerosonde flew through Ophelia at 2,500 foot altitude, and measured winds of 74 knots. The project is described in detail on the NOAA Hurricane Research Division's web site. The objective is to use the pilotless aircraft in regions where it is too dangerous for humans to fly:

Simply stated, continuous observation of thermodynamic (temperature and moisture) and kinematic (wind) structure of the near-surface hurricane environment has never been documented in a hurricane. This environment, where the atmosphere meets the sea, is critically important since it is where the ocean's warm water energy is directly transferred to the atmosphere just above it. The tropical cyclone surface layer is also important because it is where we find the strongest winds in a hurricane and coincidentally, the level at which most of us live (i.e. at/near the surface). As such, observing and ultimately better understanding this region of the storm is crucial if we hope to improve our ability to make accurate forecasts of TC intensity change. Enhancing this predictive capability would not only save our economy billions of dollars but more importantly it would save countless lives.

Well done, Aerosonde Corporation and NOAA!

Jeff Masters

Updated: 4:15 PM GMT on September 17, 2005

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TD 17 coming soon--and a scientific first!

By: JeffMasters, 9:06 PM GMT on September 16, 2005

TD 17?
Substantial deep convection has developed in the past few hours in association with well-organized tropical wave about 500 miles east-southeast of the Windward Islands. Spiral banding is more and more conspicuous with each visible satellite image, and if the present trend continues, NHC wil probably initiate advisories on Tropical Depression 17 tonight or tomorrow morning.

The system is in a favorable environment for intensification, now that it has gotten farther from the Equator and can take advantage of the increased spin a higher Coriolis force offers at higher latitudes. Wind shear has decreased to 5 - 10 knots, and the upper-level winds appear favorable--a small upper-level anticyclone is over the wave, and should provide good outflow. Some weak outflow is apparent to the south, and moderately good outflow to the north. Water temperatures are about 29.5C (85F), and increase to about 30C (86F) near the Lesser Antilles Islands.

The early track models are unreliable. The GFDL disippates the system immediately, and the BAMM has been flip-flopping, alternately taking it west-northwest into the Caribbean or northwest, missing the Leeward Islands entirely. The GFS and UKMET models both take the system to the northernmost Leeward Islands, just east of Puerto Rico. The correct solution will depend upon how quickly the system develops, and how quickly a large mid-Atlantic trough north of the islands lifts out. All interests in the Lesser Antilles Islands need to monitor this storm, it has the potential to grow into a hurricane about the time it reaches the islands on Monday.


Figure 1. Early track model runs for the disturbance approaching the Lesser Antilles.

Blob northeast of Puerto Rico
A disturbance northeast of Puerto Rico continues to generate some impressive clusters of thunderstorms, but is not a threat to develop into a tropical depression until Saturday at the earliest. This disturbance is expected to move westward towards the Cuba and the Bahama Islands the next few days. Strong upper level winds out of the west are creating about 10 - 20 knots of shear over the disturbance, down from 20 knots yesterday. The shear should continue to drop the next few days, and may be low enough by Sunday to allow a tropical depression to form. The system could threaten South Florida and Cuba as it continues to track west. Several computer models indicate that the disturbance is more likely to develop once it reaches the Gulf of Mexico, and pose the greatest threat to Mexico. There are no early computer model track points for this disturbance yet, I will post them when they become available.

ITCZ
The Intertropical Convergence Zone (ITCZ), the band of strong thuderstorms between Africa and South America, has historically been the source of many of the severe hurricanes that affect us in September. These "Cape Verde" type storms, so named because they originate from disturbances in the ITCZ near the Cape Verde Islands, have yet to make an appearance during this peak time of hurricane season. The ITCZ has become very active the past few days, and is forecast to continue to remain active the next two weeks. I expect at least one major Cape Verdes type hurricane to form by the end of September. The main activity is across the eastern and central Atlantic is at about 8N latitude, which is probably too far south to generate a tropical cyclone. If some of this activity works its way to 9N, we may have a better chance of development in this area.

Ophelia: a scientific first
A scientific first was accomplished in Ophelia this afternoon--the first ever remotely-piloted aircraft to do a successful penetration of a tropical cyclone flew through Ophelia at 2,500 foot altitude. The drone measured winds of 74 knots. The project is described in detail on the NOAA Hurricane Research Division's web site. The objective is to use the pilotless aircraft in regions where it is too dangerous for humans to fly:

Simply stated, continuous observation of thermodynamic (temperature and moisture) and kinematic (wind) structure of the near-surface hurricane environment has never been documented in a hurricane. This environment, where the atmosphere meets the sea, is critically important since it is where the ocean's warm water energy is directly transferred to the atmosphere just above it. The tropical cyclone surface layer is also important because it is where we find the strongest winds in a hurricane and coincidentally, the level at which most of us live (i.e. at/near the surface). As such, observing and ultimately better understanding this region of the storm is crucial if we hope to improve our ability to make accurate forecasts of TC intensity change. Enhancing this predictive capability would not only save our economy billions of dollars but more importantly it would save countless lives.

Well done, Aerosonde Corporation and NOAA!

Ophelia has intensified a bit this afternoon, with the pressure falling 3 mb. This will be short-lived, however. In fact, the 5pm EDT hurricane hunter eye report found the pressure had risen 2 mb. Ophelia will pass out of the warm Gulf Stream waters and encounter waters as cold as 70F Saturday. She will still generate some trouble on her trek north; expect a 1 - 3 foot storm surge for southeast Massachusetts and Nova Scotia, 1 - 3 inches of rain, and sustained winds up to 40 mph as Ophelia brushes by.

While Ophelia did dump it share of heavy rain--around 5 - 7 inches near Wilmington, and over 10 inches around Cape Fear, south of Wilmington--the rain was mostly confined to the coast, and did not cause widespread flooding problems. Ophelia's winds also did relatively light damage--sustained hurricane force winds (74 mph) were only observed at one location, on Cape Lookout near the Outer Banks. The highest wind gusts measured were 92 mph on Cape Lookout and 83 mph at Cape Hatteras. The storm surge was what caused the main havoc with Ophelia--surges heights of up to 10 - 12 feet were observed along the Neuse River north of Wilmington. Preliminary damage estimates put Ophelia's damage to North Carolina over $10 million, but less than $100 million.


Figure 2. Estimated rainfall from the Morehead City radar for Ophelia's passage.

Jeff Masters

Updated: 9:27 PM GMT on September 16, 2005

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Ophelia, and 3 new threats

By: JeffMasters, 1:55 PM GMT on September 16, 2005

Ophelia
Yesterday, I was trying to imagine a day when I wouldn't talk about Ophelia moving slowly. Today is not the day :-( since Ophelia was still stalled out near Cape Hatteras this morning. However, the past few hours the Norfolk long range radar loop has shown a dramatic increase in Ophelia's forward speed and turn to the north-northeast. There is hope, then--tomorrow I will not have to talk about Ophelia moving slowly! I expect that the trough giving me a rainy day here in Michigan has now nabbed Ophelia and will swing her up the East Coast at a respectable speed today and tomorrow. Ophelia will still generate some trouble on her trek north; expect a 1 - 3 foot storm surge for southeast Massachusetts and Nova Scotia, 1 - 3 inches of rain, and sustained winds up to 40 mph as Ophelia brushes by.

While Ophelia did dump it share of heavy rain--around 5 - 7 inches near Wilmington, and over 10 inches around Cape Fear, south of Wilmington--the rain was mostly confined to the coast, and did not cause widespread flooding problems. Ophelia's winds also did relatively light damage--sustained hurricane force winds (74 mph) were only observed at one location, on Cape Lookout near the Outer Banks. The highest wind gusts measured were 92 mph on Cape Lookout and 83 mph at Cape Hatteras. The storm surge was what caused the main havoc with Ophelia--surges heights of up to 10 - 12 feet were observed along the Neuse River north of Wilmington. Preliminary damage estimates put Ophelia's damage to North Carolina over $10 million, but less than $100 million.


Figure 1. Estimated rainfall from the Morehead City radar for Ophelia's passage.

Wave nearing the Windward Islands
A well-organized tropical wave 600 miles east-southeast of the Windward Islands has the potential to develop into a tropical depression in the next few days. The wave's surface circulation is better defined today, and is visible on both satellite imagery and QuikSCAT satellite measurements. Deep convection is limited, but has increased since yesterday. The wave, now located near 10N 50W, has moved away from the equator some, and has a better chance for development as it continues to gain latitude while moving west-northwest at 15 mph. Wind shear has decreased to about 10 knots, and the upper-level winds appear favorable--a small upper-level anticyclone is over the wave, and should provide good outflow if more deep convection starts to fire up.

The early track models are split, withe GFDL disippating the system immediately and the BAMM taking it into the Caribbean. The BAMM solution is radically different from the one six hours ago, which showed the large mid-Atlantic trough turning the system northwestward and missing the Leeward Islands. I expect the new BAMM solution is correct; the system is too shallow and too far south to get caught up by the mid-Atlantic trough, and will cross into the Eastern Carribean Monday. I suspect that the system will organize too slowly to pose a hurricane threat to the Leeward or Windward Islands. Hurricane Emily took a very similar path to this disturbance and developed into a hurricane right when it crossed the Windward Islands into the Caribbean, but was already a tropical storm when it reached 50W longitude, where our disturbance is today.


Figure 1. Early track model runs for the disturbance approaching the Windward Islands.

Blob northeast of Puerto Rico
A concentrated area of thunderstorms northeast of Puerto Rico has developed in the base of a large trough of low pressure. This disturbance will separate from the trough and move westward towards the Bahama Islands the next few days. Strong upper level winds out of the west are creating about 15 knots of shear over the disturbance, down from 20 knots yesterday. The shear should continue to drop the next few days, and may be low enough by Sunday to allow a tropical depression to form. The system should be in the Bahama Islands by then, and could threaten South Florida and Cuba as it continues to track west. Several computer models indicate that the disturbance is more likely to develop once it reaches the Gulf of Mexico, and pose the greatest threat to Mexico or Texas. There are no early computer model track points for this disturbance yet, I will post them when they become available.

ITCZ
The Intertropical Convergence Zone (ITCZ), the band of strong thuderstorms between Africa and South America, has historically been the source of many of the severe hurricanes that affect us in September. These "Cape Verde" type storms, so named because they originate from disturbances in the ITCZ near the Cape Verde Islands, have yet to make an appearance during this peak time of hurricane season. The ITCZ has become very active the past few days, and is forecast to continue to remain active the next two weeks. I expect at least one major Cape Verdes type hurricane to form by the end of September.

One candidate might be an area of distubed weather near 9N 36W. The QuikSCAT satellite shows a surface circulation here, and we'll have to watch this disturbance as it tracks westward the next few days.

Jeff Masters

Updated: 4:46 PM GMT on September 16, 2005

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Ophelia, wave nearing Windward Islands, and blob near Puerto Rico

By: JeffMasters, 8:19 PM GMT on September 15, 2005

Wave nearing Windward Islands
A well-organized tropical wave 850 miles east of the Windward Islands has not improved in organization this afternoon, but still has the potential to develop into Tropical Depression 17 in the next few days. The wave has a decent surface circulation visible on satellite imagery and QuikSCAT satellite measurements, but deep convection is limited. The wave, located near 9N 48W, is suffering from being too far south and from 10 - 15 knots of wind shear. The disturbance is expected to continue moving west-northwest at 10-15 mph the next few days into a region with less shear. The upper level environment is favorable--an anticyclone has formed on top of it, which should provide very favorable outflow for any deep convection that fires up.


Figure 1. Early track model runs for the disturbance that may turn into Tropical Depression 17.

Blob north of Puerto Rico
A pronounced area of thunderstorms has developed north of Puerto Rico this afternoon, in the base of a large trough of low pressure over the Atlantic. This disturbed area lies in an area of uniform easterly winds that will blow the thunderstorms to the west towards Cuba and the Bahamas. Upper level wind shear is currently high over the disturbance--about 20 knots--but is expected to drop once the disturbance reaches the Bahama Islands on Saturday or Sunday. A tropical depression could form then or early next week when the disturbance crosses into the Gulf of Mexico.

Shear values in general over most of the Gulf of Mexico and Caribbean are expected to drop to very low levels favorable for tropical development during the next week, and I think it is likely that we will see a tropical storm in either the Gulf or Caribbean then.

Ophelia
I'm trying to imagine a day when I don't talk about Ophelia moving slowly, but today is not the day. Perhaps tomorrow; the next trough swinging off the East Coast should be able to pick her up and move her out late in the day.

Ophelia is a shell of her former self. The eyewall has disintegrated, and the latest SFMR wind data from the NOAA hurricane hunters shows just a very small area of hurricane force winds over the water. Cooler waters, dry air, and wind shear are all taking their toll on Ophelia, and by the time she races past Cape Cod on Saturday, the worst she will be able to do there is generate wind gusts of 40 mph.


Figure 2. Winds in Ophelia at 12:30pm EDT today measured by the NOAA hurricane hunters.

Storm surge levels observed last night in Bogue Sound, which is the bay between Morehead City and its barrier island, reached seven feet--near the record levels set there from Category 3 Hurricane Hazel in 1954. The storm surge reached 10 feet in some of the smaller creeks in the Neuse River and may have reached 12 feet, a remarkably high storm surge for what was a tropical storm for that area. High storm surges can result from just tropical storm force winds, if they blow over a large area for a really long time, like Ophelia's did.


Figure 3. Storm Surge heights measured in Ophelia.

For those of you who can handle a 1.6Mb animation, the radar loop from Morehead City, NC during the time Ophelia's northern eyewall passed over the city is fascinating. The turbulence created by having part of the eyewall over land and part over water created some smaller vorticies along the inside edge of the eyewall.

While Ophelia did dump it share of heavy rain--around 5 - 7 inches near Wilmington, and over 10 inches around Cape Fear, south of Wilmington--the rain was mostly confined to the coast, and did not cause widespread flooding problems. Ophelia's winds also did relatively light damage--sustained hurricane force winds (74 mph) were only observed at one location, on Cape Lookout near the Outer Banks. The storm surge was what caused the main havoc with Ophelia.


Figure 4. Estimated rainfall from the Morehead City radar for Ophelia's passage.

Jeff Masters

Updated: 8:25 PM GMT on September 15, 2005

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Ophelia departing, TD 17 arriving?

By: JeffMasters, 4:15 PM GMT on September 15, 2005

Storm surge levels observed last night in Bogue Sound, which is the bay between Morehead City and its barrier island, reached seven feet--near the record levels set there from Category 3 Hurricane Hazel in 1954. The storm surge reached 10 feet in some of the smaller creeks in the Neuse River and may have reached 12 feet, a remarkably high storm surge for what was a tropical storm for that area. High storm surges can result from just tropical storm force winds, if they blow over a large area for a really long time, like Ophelia's did.


Figure 1. Storm Surge heights measured in Ophelia.

For those of you who can handle a 1.6Mb animation, the radar loop from Morehead City, NC during the time Ophelia's northern eyewall passed over the city is fascinating. The turbulence created by having part of the eyewall over land and part over water created some smaller vorticies along the inside edge of the eyewall.

While Ophelia did dump it share of heavy rain--around 5 - 7 inches near Wilmington, and over 10 inches around Cape Fear, south of Wilmington--the rain was mostly confined to the coast, and did not cause widespread flooding problems. Ophelia's winds also did relatively light damage--sustained hurricane force winds (74 mph) were only observed at one location, on Cape Lookout near the Outer Banks. The storm surge was what caused the main havoc with Ophelia.


Figure 2. Estimated rainfall from the Morehead City radar for Ophelia's passage.

Ophelia is very slowly lumbering out to sea, and is a mere shell of her former self. The eyewall has disintegrated, and the latest hurricane hunter flight found a rising pressure (987 mb) and winds at flight level (78 knots) that may support downgrading Ophelia to a tropical storm this afternoon. Cooler waters, dry air, and wind shear are all taking their toll on Ophelia, and by the time she races past Cape Cod on Saturday, the worst she will be able to do there is generate wind gusts of 40 mph.

TD 17?
A well-organized tropical wave 900 miles east of the Windward Islands is slowly improving in organization and may become Tropical Depression 17 by tommorow. The wave, located near 9N 47W, is a little too far south to develop quickly, but is moving WNW towards higher latitudes. The shear over the wave is marginal for development, about 10 - 15 knots, but is expected to drop by this evening. Wind measurements from the QuikSCAT satellite show that an elongated surface circulation has already formed, but winds around the disturbance are below 20 knots. The upper level environment is favorable--an anticyclone has formed on top of it, which should provide very favorable outflow for any deep convection that fires up. The disturbance is expected to continue moving west-northwest at 10-15 mph the next few days, then possibly slow down and turn more northwest under the steering influence of a large mid-Atlantic trough.


Figure 4. Early track model runs for the disturbance that may turn into Tropical Depression 17. The 2am GFDL run disippated the disturbance immediately.

Elsewhere in the tropics
No other tropical storm developent is expected elsewhere in tropics through tomorrow. However, conditions for development are expected to improve over much of the tropical Atlantic over the coming week, including the Caribbean and Gulf of Mexico.

Jeff Masters

Updated: 4:22 PM GMT on September 15, 2005

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Ophelia's near-record storm surge

By: JeffMasters, 1:42 PM GMT on September 15, 2005

Storm surge levels observed last night in Bogue Sound, which is the bay between Morehead City and its barrier island, reached seven feet--near the record levels set there from Category 3 Hurricane Hazel in 1954. The storm surge values ranged as high as 10 - 12 feet in some of the smaller creeks in the Neuse River near New Bern, a remarkably high storm surge for what was a tropical storm for that area.


Figure 1. Storm Surge heights measured in Ophelia.

For those of you who can handle a 1.6Mb animation, the radar loop from Morehead City, NC during the time Ophelia's northern eyewall passed over the city is fascinating. The turbulence created by having part of the eyewall over land and part over water created some smaller vorticies along the inside edge of the eyewall.


Figure 2. Estimated rainfall from the Morehead City radar for Ophelia's passage.

I'll post a more detailed update on Ophelia and the developing tropical wave approaching the Leeward Islands by noon today.

Jeff Masters

Updated: 1:43 PM GMT on September 15, 2005

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First hurricane force winds observed on the coast

By: JeffMasters, 10:54 PM GMT on September 14, 2005

The Cape Lookout CMAN station on the tip of Cape Lookout measured a sustained wind of 65 knots, gusting to 78 knots, at 8pm EDT. These sustained winds are exactly minimal hurricane force, so Ophelia has qualified as a hurricane strike on the U.S. I'm not sure why NHC extended the hurricane warning all the way to the Virginia border; the odds of anyplace besides Cape Lookout and Cape Hatteras getting sustained hurricane force winds is pretty low.

The north eyewall of Ophelia is pounding the North Carolina coast, and has knocked out power to the NWS Newport/Morehead City office. Their backup generator has also failed, so the Wakefield, VA NWS office will be assuming service backup duties. Apparently the Morehead City radar still has power, since we are still getting radar images from there.

For those of you who can handle a 1.6 Mb animation, the 40-frame radar animation from Morehead City, NC during the time Ophelia's northern eyewall passed over the city is fascinating. The turbulence created by having part of the eyewall over land and part over water created some smaller vorticies along the inside edge of the eyewall.




Elsewhere in the tropics
A large tropical wave near 9N 43W or about 1000 miles east of Venezuela and the Windward Islands was very disorganized this morning, but has become quite well organized this evening. Upper level wind shear is 10 - 15 knots and falling, and some upper level outflow has developed on the north side of the disturbance. Winds observed by the QuikSCAT satellite show two circulation centers associated with the disturbance, one near 9N 43W and the other near 11N 46W. This disturbance has the potential to develop into a tropical depression as early as Friday. Another disturbance south of the Cape Verde Islands, near 8N 28W is also starting to develop some impressive deep convection. However, this disturbance lies at the south edge of a large area of dry, dust-laden air which will slow any development that might occur.

Jeff Masters

Updated: 2:05 AM GMT on September 15, 2005

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Ophelia churns up NC coast

By: JeffMasters, 7:48 PM GMT on September 14, 2005

The north and west eyewall of Ophelia have whipped near-hurricane force winds over Wilmington, NC and the surrounding waters the past few hours. NOAA buoy 41013 located south of Wilmington, saw maximum sustained winds of 63 mph, gusting to 72 mph. A NOAA reporting station at Wrightville Beach North Carolina recorded 6-minute average wind speed of 68 mph with a gust to 77 mph. A Wilmington Personal Weather Station, NC State Ports, recorded maximum sustained winds of 66 mph, gusting to 72 mph at 2:25pm. A peak gust of 78 mph occured there a few minutes later. The NOAA aircraft's SFMR instrument measured surface winds of 65 kt (minimum hurricane force), over a small area on the southwest side of the hurricane at 12:30pm today. Thus, NHC's estimate of hurricane force winds extending out 50 miles from the center is misleading; there are probably only a few small pockets of sustained hurricane force winds at the surface. Given that Ophelia now has an easterly component of motion and is expected to move nearly parallel to the coast, it is unlikely that any portion of North Carolina will see sustained hurricane force winds today. On Thursday, Cape Hatteras may see hurricane force winds, but I think this is unlikely, given the track of the storm and the possibility that she may weaken. The winds at the Cape Lookout CMAN station located in the just outside the east eyewall should be interesting to watch the next 18 hours, as Ophelia should pass directly overhead. Peak winds last hour were 57 mph, gusting to 66 mph there.


Figure 1. Surface wind estimates at 12:30pm this afternoon from the NOAA aircraft's SFMR instrument show only a small area of hurricane force winds (65 knots) on Ophelia's southwest side.

Radar out of Morehead City, NC has shown little change in the storm's organization the past few hours, and the last six hours of hurricane hunter reports have shown a relatively constant pressure, oscillating between 979 and 980 mb. Ophelia is likely as strong as she is going to get, and I expect we will see some slow weakening the next 36 hours as she continues her slow march along the coast.

The predominant danger from Ophelia remains her storm surge, which is more characteristic of a strong Category 1 or weak Category 2 hurricane. A long-lasting storm surge of 6 - 8 feet is possible in many coastal areas of North Carolina. Already, storm surges of up to 7 feet have been reported in some areas, equalling the storm surges generated from Category 2 Hurricane Isabel in 2003. Isabel did about $130 million in damage to North Carolina, and I expect we'll see damages around the $100 million mark for Ophelia.



Flooding of low-lying areas from rain could be a problem in some places; Oak Island south of Wilmington, NC on Cape Fear has already received nine inches or rain. Another 5 - 10 inches of rain is likely from this wet, slow-moving storm.


Figure 2. Rainfall estimates from the Wilmington Doppler radar.

Elsewhere in the tropics
A large tropical wave near 9N 43W or about 1000 miles east of Venezuela and the Windward Islands was very disorganized this morning, but has become quite well organized this afternoon. Upper level winds shear is 10 - 15 knots and falling, and some upper level outflow has developed on the north side of the disturbance. Winds observed by the QuikSCAT satellite show two circulation centers associated with the disturbance, one near 9N 43W and the other near 11N 46W. This disturbance has the potential to develop into a tropical depression later this week or early next week. Another disturbance south of the Cape Verde Islands, near 8N 28W is also starting to develop some impressive deep convection. However, this disturbance lies at the south edge of a large area of dry, dust-laden air which will slow any development that might occur.

New community chat room
For those of you tired of hitting refresh constantly and wanting to talk about the tropics, we now have a new community chat room. Just click on the link at the upper right of the blog page.

http://www.wunderground.com/community/chat.asp

Jeff Masters

Updated: 10:41 PM GMT on September 14, 2005

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The usual Ophelia story

By: JeffMasters, 2:25 PM GMT on September 14, 2005

Ophelia has now spent nine days lurching around the ocean areas south of North Carolina, and is certainly not in a hurry to end the ordeal. She'll be with us at least one more day before finally clearing the Outer Banks of North Carolina and heading out to sea. Radar out of Wilmington, NC has shown a slow increase in intensity and coverage of the rainfall the past 24 hours. Ophelia will soon be moving over waters of approximately 80F (26.5C), which is the limiting temperature below which a hurricane cannot intensify. Because of this factor, and the fact that Ophelia's northern eyewall is over land, little or no further intensification is likely for the remainder of Ophelia's trek along the coast. The upper level outflow remains good, and wind shear is low, so Ophelia should still stay a large and well-organized storm through the next two days.

Although NHC has been advertising peak winds of 80 mph and hurricane force winds extending out 50 miles from the center, the actual maximum sustained winds measured at the surface by NOAA buoy 41013 when it was in the north eyewall, were only 54 mph. At 8:00 am the Bald Head Island Marina measured a gust of 77 mph. Wilmington International Airport measured sustatined winds of 41 mph and a peak wind gust of 56 mph this morning. Scattered power outages have occurred across the area, and there are reports of minor roof damage. The NOAA aircraft's SFMR instrument measured surface winds of 65 kt (minimum hurricane force), over a small area on the southwest side of the hurricane at 12:30pm today. Thus, NHC's estimate of hurricane force winds extending out 50 miles from the center is misleading; there are probably only a few small pockets of sustained hurricane force winds at the surface. Given that Ophelia now has an easterly component of motion and is expected to move nearly parallel to the coast, it is unlikely that any portion of North Carolina will see susustained hurricane force winds today. On Thursday, Cape Hatteras may see hurricane force winds, but I think this is unlikely, given the track of the storm and the possibility that she may weaken.


Figure 1. Surface wind estimates at 12:30pm this afternoon from the NOAA aircraft's SFMR instrument show only a small area of hurricane force winds (65 knots) on Ophelia's southwest side.

The predominant danger from Ophelia remains her storm surge, which is more characteristic of a strong Category 1 or weak Category 2 hurricane. A long-lasting storm surge of 6 - 8 feet is possible in many coastal areas of North Carolina.



Flooding of low-lying areas from rain could be a problem in some places; areas just south of Wilmington, NC on Cape Fear have already received 4 - 5 inches or rain. Another 5 - 10 inches of rain is likely from this wet, slow-moving storm. If eastern North Carolina were not under mild drought conditions, this would have been a much more serious storm.

Elsewhere in the tropics
There are currently no other threats in the tropics worthy of attention. However, the ITCZ is becoming more active, and most of the global computer models are consistently predicting tropical storm formation early next week in the region between Africa and the Leewards Islands. The amount of dry, dust-laden Saharan air over the tropics has declined in recent days, making the area more favorable for tropical storm development. A large new dust storm is over the Cape Verde Islands today, so development in that area is not expected.

New community chat room
For those of you tired of hitting refresh constantly and wanting to talk about the tropics, we now have a new community chat room. Just click on the link at the upper right of the blog page.

http://www.wunderground.com/community/chat.asp

Jeff Masters

Updated: 5:35 PM GMT on September 14, 2005

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Ophelia lumbering towards the coast

By: JeffMasters, 9:55 PM GMT on September 13, 2005

Ophelia is lumbering towards the coast at a snail's pace of 4mph, and remains over warm enough water (82-83F) to keep a slow strengthening trend going. Long range radar out of Wilmington, NC shows an modest increase in intensity and coverage of the rainfall, but the inner eyewall of about 20 miles diameter that was trying to form this morning has collapsed. Now that Ophelia is moving, the upwelling of cold water stirred up by her winds is not going to be an inhibiting factor. However, the water temperatures within about 80 miles of the coast cool off to about 78 - 80F, and this should put a halt to Ophelia's slow intensification once she gets close to the coast on Wednesday night or Thursday morning.

Although NHC has been advertising Ophelia as having peak winds of 70 mph, the actual peak winds measured at the surface by buoys is 50 mph. Apparently the stronger winds at higher altitudes measured by the Hurricane Hunters and by Doppler radar are not mixing down to the surface as efficiently as usual for a hurricane. The NOAA aircraft's SFMR instrument has measured surface winds of 55 kt (63 mph), but this estimate is not supported by buoy measurements, and the SFMR winds are probably too high by 5 knots.

Shear is low (5 knots) and the upper-level outflow good, but there is still too much dry air and cool water surrounding Ophelia to support anything stronger than a 80 mph Category 1 hurricane. The chances of a coastal observation site actually recording sustained winds of hurricane force (74 mph) are probably about 20%. Wind damage from Ophelia should be low, but her winds have had a lot of time to pile up a big mound of water near her center, and the storm surge of 4 - 6 feet will cause most of this storm's damage.



Flooding of low-lying areas from rain could be a problem in some places; areas just south of Wilmington, NC have already received 4 - 5 inches or rain. Another 5 - 10 inches of rain is likely from this wet, slow-moving storm. If eastern North Carolina were not under mild drought conditions, this would have been a much more serious storm.


Figure 1. Surface wind estimates this afternoon from the NOAA aircraft's SFMR instrument show a large area of tropical storm force winds, primarily on the west side.

Jeff Masters

Updated: 10:05 PM GMT on September 13, 2005

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Ophelia stuck yet again

By: JeffMasters, 1:55 PM GMT on September 13, 2005

Ophelia is stuck in place yet again, but this time she threw anchor over some relatively warm water (83F)--right over the Gulf Stream, where a deep, 75-meter thick layer of warm water exists. As a result, Ophelia is slowly strengthening again, and long range radar out of Wilmington, NC is showing the beginnings of an inner eyewall of about 20 miles diameter trying to form inside Ophelia's 100-mile wide cloud-free center. The deep warm water should resist the mixing effect of her winds and prevent water cooler than 80F from upwelling and inhibiting Ophelia's strengthening, at least for the 12 - 18 hours that she is expected to remain stationary.

The latest hurricane hunter flight at 9:20 am EDT found about the same pressure as always, 989 mb, and unimpressive flight level peak winds of 66 knots on the northeast side. Ophelia is in reality a weaker tropical storm than advertised by the NHC; I'd estimate maximum winds near the surface are closer to 60 mph than the 70 mph advertised. Still, the storm is getting better organized, and surface winds may increase back to 70 mph later today, but not much higher. Although the shear is low (5 knots) and the upper-level outflow good, there is still too much dry air and cool water surrounding Ophelia to support anything stronger than a minimal 80 mph Category 1 hurricane. NHC is posting hurricane warnings, and this is reasonable, not so much for the expected wind damage (which should be low), but for the storm surge. Ophelia's winds have had a lot of time to pile up a big mound of water near her center, and the storm surge of 4 - 6 feet she will likely carry to shore in her current state as a tropical storm is more characteristic of a Category 1 hurricane.



The exact landfall point for Ophelia is much less important than for most hurricanes; Ophelia doesn't have the narrow concentrated area of winds that usually make the precise landfall point such a big deal. There will be a large area of the coast that will receive tropical storm force winds, which extend out about 160 miles from the center, an exceptionally large area for a tropical storm. Flooding from rain could be a problem in some places; areas near Wilmington, NC have already received 2 - 3 inches, and will get much more from this very wet storm. Fortunately, much of eastern North Carolina is under mild drought.


Figure 1. Rainfall estimate from the Wilmington radar. The estimates in northern NC at the top of the image are bogus.

Computer model forecasts
All of the computer model forecasts keep Ophelia puttering around her current location most of today, but then turn her north and then northeast just offshore Cape Fear, NC and accelerate her rapidly northeastward out to sea. Some of the models indicate that New England (particularly Cape Cod, MA) and Nova Scotia may receive tropical storm force winds from Ophelia on Friday and Saturday, respectively.

Elsewhere in the tropics
The rest of the tropics are quiet, and it is likely we will get about a one week break in the action. Next week, several of the long-range global models indicate that conditions for tropical storm formation are expected to improve over much of the tropical Atlantic.

Jeff Masters

Updated: 5:18 PM GMT on September 13, 2005

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Ophelia speeds up

By: JeffMasters, 8:29 PM GMT on September 12, 2005

Ophelia has decided to start moving, and according to the NHC, is now tracking towards the northwest at about 3 mph. The motion appears much faster--closer to 8 mph, looking at satellite images--but the last two center fixes by the hurricane hunters yeild a speed of about 4 mph, and NHC does some smoothing to take out the well-documented wobbles (trocoidal motion) of these storms, which reduced the forward speed estimate to 3 mph. In any case, the outermost rainband has moved about 9 mph towards the South Carolina coast this afternoon, and will spread heavy rain and 20 - 30 mph winds from Charleston, SC northwards to Wilmington, NC this afternoon and evening. Long range radar out of Wilmington, NC has a good view of these spiral bands. None of the computer forecast models quite anticipated this faster motion, but NHC is sitcking with their landfall near Wilmington, NC, with the storm passing up the length of the North Carolina coast and moving out to sea near Cape Hatteras.

The exact landfall point for Ophelia is much less important than for most hurricanes; the dry air that has plauged the storm the past two days destroyed her eyewall today, and Ophelia doesn't have the narrow concentrated area of winds that usually make the precise landfall point such a big deal. There will be a large area of the coast that will receive tropical storm force winds and a storm surge of 4 -6 feet characteristic of a Category 1 hurricane. Tropical storm force winds extend out about 160 miles from the center, an exceptionally large area for a tropical storm.


Intensity forecast
The latest hurricane hunter mission was at 1:19pm EDT, and showed a strong tropical storm with no eyewall, a central pressure of 989 mb, and peak winds of just 69 knots on the northwest side. Ophelia has moved to an area of ocean she hasn't traversed yet where the sea surface temperatures are a little warmer--about 82 F (a minimum temperature of 80 F is needed to maintain a hurricane). However, there are cooler waters of 79 F near the coast and back where she came from, so there is not much warm water to work with. Ophelia continues to pull dry air off of the coast, and this factor combined with the marginal sea surface temperatures will keep Ophelia from attaining anything more than a weak Category 1 status the next three days. Given that her eyewall has collapsed and will probably take 2 - 3 days to rebuild in a best-cast scenario, I believe that Ophelia will remain a tropical storm the next three days.


Figure 1. Surface winds in Ophelia this morning as seen from the NOAA hurricane hunter aircraft.

Computer model forecasts
Now all of the computer model forecasts take Ophelia northeast past Cape Hatteras and out to sea, but at varying speeds. The NOGAPS model indicates that she might linger near North Carolina until the end of the week before finally getting taken out to sea. The Canadian model no longer thinks Ophelia will move southwest across northern Florida, and has joined the chorus of models calling for a northeast turn past Cape Hatteras and out to sea.

Elsewhere in the tropics
Nothing is going on. Large amounts of dry, dust-laden Saharan air cover most of the tropical Atlantic including the Caribbean Sea, and another large cloud of dust just came off the African coast today. The ITCZ is relatively quiet and too far south to spawn tropical disturbances that might grow into tropical storms. The NOGAPS model indicates a tropical storm might form out of a tropical wave east of the Windward Islands late in the week, but this seems improbable given all the dry air around.

Jeff Masters

Updated: 9:07 PM GMT on September 12, 2005

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Don't believe the models

By: JeffMasters, 1:33 PM GMT on September 12, 2005

Don't believe any of the computer forecast models or the official NHC forecast--no one knows where Ophelia is going. Ophelia is trapped between two large and strong high pressure systems, and will continue to behave unpredictably. The 5am NHC discussion called it this way: "None of the reliable dynamical models have been immune from significant track forecast shifts during the past day or two in this very difficult scenario." In other words, we have no idea where Ophelia is going.

A slow westward drift has been the trend the past day or so, and several of the models show a slow westward or northwestward drift the next two days. Thus, it is reasonable to anticipate that Ophelia's outer rain bands will start to impact the North Carolina and South Carolina coasts this afternoon through tomorrow, bringing localized heavy rain and minor flooding. The usually-reliable GFS model's latest run at 06Z (2am EDT) this morning shows Ophelia hitting Charleston as a strong tropical storm Tuesday morning, and the GFDL thinks Ophelia will be a Category 1 hurricane hitting South Carolina Tuesday night. The other models disagree, letting Ophelia wander off the coast the next two days, and forecast that by Wednesday, a weak trough will push off the East Coast and take Ophelia northward across eastern North Carolina and out to sea. However, the models have trended towards making this trough weaker and weaker. There now appears to be a significant possibility that the trough will fail to pick up Ophelia, high pressure will build back in, and she will wander around the ocean waters near Cape Hatteras for a few more days. The Canadian model has a rather omininous solution--the high pressure that builds in will be strong enough to push Ophelia southwestward, across northern Florida, and into the Gulf of Mexico five days from now. I pooh-poohed this solution when I saw it yesterday, but now this forecast cannot be discounted. The Canadian model has been suggesting that the trough would fail to pick up Ophelia for three runs in a row now, and the NOGAPS and UKMET are starting to show the same thing. In any case, none of these models should be taken very seriously; this is an extremely difficult forecast situation, and trying to predict what Ophelia will do five days from now, let alone tomorrow, will involve more luck than skill.

Intensity forecast
The latest hurricane hunter mission was at 8:30am EDT, and showed a slightly weaker storm with a poorly-formed eyewall, a central pressure of 988 mb, and peak winds of just 48 knots on the west side. The crew will find stronger winds once they penetrate the north eyewall where the strongest winds are, but Ophelia might get downgraded to a tropical storm today.


Figure 1. Surface winds in Ophelia yesterday afternoon as seen from the NOAA hurricane hunter aircraft.

Dry air continues to be Ophelia's bane; a large amount of it has wrapped into the core of the hurricane and disrupted the convection on the west side. There is still plenty of dry air on her northwest side, and this should continue to be a problem for her the next few days. Cold water stirred up from down deep by Ophelia's winds will also continue to be a problem as she wanders over the same ocean area for multiple days. On the plus side for intensification, wind shear remains lows, about 5 - 10 knots out of the northwest. The upper-level ouflow pattern remains good, and the overall organization of Ophelia is strong. Given all these factors, neither significant strengthening or weakening is likely the next two or three days, and Ophelia will remain a strong tropical storm or weak Category 1 hurricane during this period.

Elsewhere in the tropics
Nothing is going on. Large amounts of dry, dust-laden Saharan air cover most of the tropical Atlantic including the Caribbean Sea.

Jeff Masters

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Ophelia stuck again

By: JeffMasters, 3:35 PM GMT on September 11, 2005

Ophelia seems intent on going nowhere in a hurry, and is stuck some 250 miles south of Cape Hatteras, NC. Steering currents are very weak, and Ophelia is expected to stay stuck through Monday and probably Tuesday as well. Finally, on Wednesday, a trough of low pressure is forecast to push off the East Coast and nudge Ophelia onto a northward track over North Carolina as a Category 1 hurricane, and perhaps on to New England Thursday or Friday as a 50 mph tropical storm. Some forecast models indicate a slow drift towards the coast may occur Monday and Tuesday, which might bring brief heavy downpours to the Carolinas as the outer bands scrape the coast.

How believable is this forecast track? The average forecast track error for a 3-day forecast is 230 miles, which would mean Ophelia could easily make landfall in South Carolina, or completely miss the U.S. The computer models, which were almost unanimously calling for a landfall in South Carolina a day ago, have now switched to calling for a landfall in eastern North Carolina, a shift of some 300 miles in one day! These forecast models do poorly when steering currents are weak, and it would be no surprise if today's official NHC 3-day forecast is in error by 200 or 300 miles. This means that the hurricane could just as easily hit Myrtle Beach, SC as Cape Hatteras, NC--or may even pass harmlessly out to sea. Still, the fact that the models are mostly clustered over eastern North Carolina dictates that I dutifully project that residents there are at highest risk.

Ophelia's intensity remains about the same--the 9am EDT hurricane hunter mission found a central pressure of 978 mb and top flight-level winds of 74 knots, about what they've been the past day or so. Water vapor satellite imagery continues to show dry air on Ophelia's west side, and visible satellite images show a noticable lack of convection on her west side due to the dry air. The Hurricane Hunters found only a partial eyewall on their last fix, a sign that Ophelia continues to struggle with this dry air.

An additional problem for Ophelia is cold water welling up from the depths. She has been sitting in the same area for almost a day, and this has given time for the winds to churn up cold water from deep blow the hurricane. A drifting buoy to the south of Ophelia reported a 3C temperature drop yesterday, and an examination of the latest SST loop from NOAA's Hurricane Research Division shows a number of areas of upwelling cold water from the areas Ophelia has traversed. In particular, a big blue dot offshore from Cape Canaveral is visible, a location where Ophelia sat for two days stirring up cold water.

On the plus side for Ophelia, the upper-level outflow is the best it has looked, and the wind shear plauging her on the west side has dropped to 5 - 10 knots and is forecast to remain low. If Ophelia can drift away from her present location to avoid the cold waters she is stirring up, she may be able to intensity to a Category 2 hurricane. Any intensification beyond that is highly unlikely, and she will most likely remain a Category 1 hurricane through the next two or three days.

Elsewhere in the tropics
The rest of the tropics are unusually quiet in what is usually the busiest week of hurricane season.

Jeff Masters

Updated: 3:37 PM GMT on September 11, 2005

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Ophelia to miss U.S.?

By: JeffMasters, 12:33 AM GMT on September 11, 2005

The latest 18Z (2pm EDT) runs of the GFDL and GFS models are in, and both continue the trend we've been seeing the past day or so of taking Ophelia more and more north. Both of these models are joining the NOGAPS model in taking Ophelia just over or offshore of Cape Hatteras, NC. It is becoming inreasingly likely that Ophelia will deliver at worst a glancing blow to the Outer Banks of North Carolina, and spare the U.S. a direct hit.



Before we get too enthusiastic about this development, we need to look at one more cycle of model runs. The 00Z (8pm EDT) runs of all the models will finish up sometime after midnight tonight. These model runs should have a much higher than average reliability. They will use data from the NOAA high-altitude jet, which is flying a high-density data mission tonight. If the models all show a continued track for Ophelia past the Outer Banks and out to sea, we can have some modest confidence that Ophelia will pull her punch.

Water vapor satellite imagery shows a substantial amount of dry air getting sucked into Ophelia on her west side, weakening her. The 7:30pm EDT hurricane hunters mission found a 1 mb increase in pressure, a gap in the south side of the eyewall, and reduced flight level winds of 73 knots. Ophelia may have lost hurricane status again.

The latest GFDL model continues to forecast that she will fight off this dry air and attain Category 2 status. The upper-level outflow is improving, but there is still 10 - 15 knots of shear from upper-level westerly winds. Category 2 status still seems like a reasonable forecast, but Category 3 is looking increasingly unlikely.

Dr. Jeff Masters

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Ophelia stronger; threat to North Carolina increases

By: JeffMasters, 6:29 PM GMT on September 10, 2005

The 1:17 pm EDT hurricane hunter mission saw no drop in pressure, but did visually observe 90 knot surface winds (105 mph), which would make Ophelia a Category 2 hurricane. The flight level winds were only 77 knots, though, so NHC will probably not upgrade Ophelia to a Category 2 storm yet. Satellite imagery shows the formation of an eye for the first time. The upper level outflow to the south is improving, and it now appears that most of the dry air that plagued the hurricane this morning has mixed out. Steady but slow intensification will likely continue, and Ophelia will probably be a Category 2 hurricane on Sunday.

The latest 8am EDT (12Z) model runs show an increased threat to North Carolina. The NOGAPS model has Ophelia hitting the Outer Banks of North Carolina Wednesday, then moving up the coast to hit Long Island, NY as a strong tropical storm or Category 1 hurricane on Thursday. The latest GFS run puts Ophelia ashore near Wilmington, NC on Wednesday, and then tracks her along the length of the NC coast and out to sea. The 12Z GFDL model has landfall occuring Tuesday near Wilmington, NC, as a Category 2 storm. The 12Z UKMET has landfall Thursday on the Outer Banks. Only the Canadian model puts Ophelia ashore in South Carolina. Overall, the models have steadily been shifting their landfall points further and further northwards, making North Carolina increasingly likely as a landfall point--and also increasing the chances that Ophelia will miss the U.S. entirely and recurve out to sea. New England and the mid-Atlantic states need to pay close attention to this storm as well; Ophelia may be coming your way late in the week next week.

The most likely scenario now appears to be a strike Tuesday or Wednesday in North Carolina as a strong Category 2 hurricane. As usual, all this is subject to a high degree of uncertainty. South Carolina is still at high risk, and Georgia still at some risk. Remember that a hurricane is not a point, and the effects of this hurricane will be felt over a wide area. Also keep in mind that the median track error for the NHC 3-day forecasts is about 230 miles, meaning that half of the time, the forecast is worse than that. Three-day intensity forecasts are in error by an average of one full category--25 mph. All residents of the Georgia, South Carolina, and North Carolina coasts need to be prepared for what will most likely be a Category 2 hurricane, but could be a Category 3.


Figure 1. Average track error of official National Hurricane Center Forecasts (in nautical miles, multiply by 1.15 get get the result in miles). Image credit: Dr. Chris Landsea, NOAA/AOML Hurricane Research Division.


Dr. Jeff Masters

Updated: 6:46 PM GMT on September 10, 2005

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Half way there

By: JeffMasters, 4:05 PM GMT on September 10, 2005

We're half way there. That's right, today is September 10, and that marks the half way point of hurricane season in the Atlantic. On average, half of all hurricanes and tropical storms occur after September 10. We still have a long way to go in what has already been the most destructive hurricane season on record.

What does the second half of hurricane season have in store for us? Well, after Ophelia departs, there is nothing brewing to take her place. The entire tropical Atlantic between Africa and the Lesser Antilles is covered with dry, dust-laden Saharan air that should suppress hurricane activity there. However, according to the September 2nd forecast issued by Dr. Bill Gray of Colorado State, tropical cyclone activity for the remainer of this hurricane season will be over 50% above average. The September-only forecast calls for five named storms and four hurricanes, with two of them major hurricanes. The October-only forecast calls for three named storms and two hurricanes with one of them a major hurricane. Normal activity for September-October is five named storms and 3.5 hurricanes, with one or two of them a major hurricane. So if you live on the coast, stock up on your hurricane supplies, review your evacuation options, and hang on for the second half of this unbelievable hurricane season of 2005.

Ophelia weakened to a tropical storm last night as the trough carrying it northeastward dumped dry air into her northwest side and attacked the west side with 20 knots of shearing winds. The trough has moved ahead of Ophelia this morning, and she is now slowing down and strengthening in response. The shear has fallen back to the 10 - 15 knots she has lived with most of her life, and the dry air is starting to mix out. The 10am EDT Air Force hurricane hunter flight found Ophelia's lowest pressure and strongest winds yet, 976 mb and 80 mph, repsectively. Long range radar out of Wilmington, NC is showing little change in what it can see of the northwestern portion of the storm, and little motion of the center.

Track forecast
Most of the major computer models show a track into South Carolina by Tuesday. The exceptions are the Canadian model, which calls for a Georgia landfall, and the NOGAPS model, which stalls Ophelia offshore for the next five days until finally bring her across Cape Hatteras, North Carolina on Friday. The official NHC forecast follows the consensus, bringing Ophelia ashore near Charleston, SC on Tuesday. The official NHC forecast has outperformed all the computer models so far for this storm, but keep in mind that the median track error for the NHC 3-day forecasts is about 230 miles, meaning that half of the time, the forecast is worse than that. All residents of the Georgia, South Carolina, and North Carolina coasts need to be prepared for what will most likely be a Category 1 or 2 hurricane, but could be a Category 3.


Figure 1. Average track error of official National Hurricane Center Forecasts (in nautical miles, multiply by 1.15 get get the result in miles). Image credit: Dr. Chris Landsea, NOAA/AOML Hurricane Research Division.

Intensity forecast
Shearing winds are expected to continue to affect Ophelia the next three days, limiting the amount of intensification that will occur. This shear will come from upper-level winds out of the west to southwest. Satellite images clearly show the effect of this shear on the hurricane--the southwest side of the storm has much reduced cloud coverage. On the plus side for the Ophelia, the counter-clockwise flow around an upper-level low to her southeast is beginning to provide an outflow channel to the south, something Ophelia has lacked her entire life. This improving outflow to the south is likely a big part of the reason for her return to hurricane strength today.

The computer models differ on how all these factors will affect Ophelia's intensity. The SHIPS model keeps her just below hurricane strength for the next three days, while the GFDL intensifies her to a Category 3 hurricane. The official NHC forecast calls for a strong Category 1 hurricane at landfall. I believe that given this storm's proven resiliency to shear, plus the opening of a new outflow channel to the south, Ophelia's intensity three days from now should be at least Category 2 and possibly Category 3. A stronger storm than that would be a major surprise.

Dr. Jeff Masters

Updated: 4:14 PM GMT on September 10, 2005

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Ophelia headed northeast

By: JeffMasters, 9:17 PM GMT on September 09, 2005

Ophelia, as expected, has regained hurricane strength. long range radar out of Melbourne shows that a full eyewall has formed, and the strength and coverage of echoes has shown a moderate increase the past 12 hours. The latest wind field analysis from the NOAA Hurricane Hunters (Figure 1 below) shows the strongest winds are on the southeast side of the hurricane. Since the storm is moving northeast, the storm's motion adds to the rotational speed of the winds to make the strongest winds occur on the southeast side (the so-called "right-front quadrant").


Figure 1. Winds Friday afternoon from the NOAA Hurricane Hunters' SFMR instrument and other sources.

Ophelia is headed out to sea--but not for long. All the computer models agree that a northeast motion will continue until late Saturday, as a weak trough pushing off the coast carries Ophelia eastward with it. High pressure is then expected to build back in, forcing Ophelia back towards the coast Sunday through Tuesday. The latest (8am EDT) runs of the NOGAPS and GFS models indicate Ophelia may hit North Carolina and track up the coast, possibly affecting New England as a tropical storm. Other models take Ophelia due west into Georgia or South Carolina before turning her northward. The track forecast is still highly uncertain, since the steering currents are still very weak. Given the recent model trends, Florida is looking less likely as a landfall location, and North Carolina needs to be increasingly concerned. There is a 10% chance that Ophelia will miss the U.S. entirely, and merely brush the Outer Banks of North Carolina and perhaps Cape Cod.

The intensity forecast, as usual, is low-confidence. Some slow intensification could occur the next 24 hours. Ophelia is over warm Gulf Stream waters and will remain so for the next four days. These waters are warm (83F), but nowhere near the temperature of the 89F waters that fueled Katrina. Ophelia has good upper-level outflow to the north, but is under 10 - 15 knots of shear from strong upper-level winds from the south, which is the main factor inhibiting her intensification. However, by Sunday, a large upper-level low currently near Puerto Rico is expected to position itself to the southeast of Ophelia and cut off the southerly shearing winds. The counter-clockwise flow around this low will provide a good ouflow channel for Ophelia to the south, something she has lacked. At the same time, the trough that is currently steering her to the northeast will be gone, allowing a more favorable upper-level outflow pattern to emerge. This combination should allow Ophelia to intensify to a Category 2 hurricane by Monday, and possibly a Category 3. Intensification beyond Category 3 status is very unlikely.

Elsewhere in the tropics
Maria and Nate are both weakening tropical storms with just a day or two left to live as they move northeastward over cold waters. The entire tropical Atlantic between Africa and the Leeward Islands is choked with dry, dust-laden air. Development in this area is not expected for many days.

Jeff Masters

Updated: 9:19 PM GMT on September 09, 2005

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Ophelia re-strengthening

By: JeffMasters, 2:14 PM GMT on September 09, 2005

Ophelia weakened last night, as strong upper-level winds out of the south continued to shear the storm's southeast side. The NOAA high-altitude jet measured a thin layer of southerly winds of 20 - 30 knots at the top of the storm, which is a significant amount of shear. Ophelia had been able to slowly strengthen the past two days in the presence of 10 - 15 knots of shearing winds, but 20 - 30 knots of shear almost always causes weakening, as we observed.

Indications are now that the shear has relaxed significantly, and Ophelia is intensifying once more. The 8am EDT hurricane hunter flight found a center pressure of 983 mb, Ophelia's lowest pressure yet. This is a drop of eight mb in just four hours, the fastest rate of intensification we've seen with this storm so far. The 10am hurricane hunter report shows the pressure has stopped dropping, though, with a 984 mb reading. Satellite imagery shows a well-organized and expanding area of outflow, but restricted on the southeast side where the shear is. The storm is growing in size, and is transitioning from a small storm to a medium-sized one.

Ophelias's surface winds are below hurricane force, but with the large fall in pressure seen by the hurricane hunters, it is only a matter of 12 hours or so until the winds increase to hurricane force once more. The maximum observed winds at 8am were only 57 knots (65 mph) at 5,000 feet altitude, but had increased to 67 knots (77 mph) on the 10am hurricane hunter eye report. The maximum temperature in the eye was 2C warmer than just outside the eye, which is not very impressive. This difference was 5C yesterday. Doppler radar wind estimates also indicate maximum winds are below hurricane force.


Figure 1. Wind speed estimates from the Melbourne Doppler radar. The red colors on the south side of the eyewall indicate strong winds blowing away from the radar. Because the radar uses the Doppler effect to measure wind speed, it cannot tell what the wind speed is when the winds don't have a component of motion towards or away from the radar. Thus, winds on the east and west eyewall are coded white (a speed of zero towards the radar) and the winds on the north eyewall are coded blue (blowing towards the radar).

Ophelia's signature on long range radar out of Melbourne is not too impressive; only half an eyewall is apparent. Very little convection exists on the east side of the storm. The radar also indicates a slow north-norhteast motion away from Florida. Looking at this radar signature, it is surprising to me that the hurricane hunters measured such a large drop in pressure.

OK, now the "where will Ophelia go?" game. We are still at least four days from a possible landfall, and steering currents are weak, so the track forecast is highly uncertain. Data from the NOAA jet's high-altitude mission last night were used to help initialize the computer models today, and they are much more tightly clustered. This gives credence to the idea of a landfall in Georgia or South Carolina sometime in the Tuesday - Thursday timeframe. The NHC did not buy this initially, prefering to see another run of the models before committing to this idea. Now, however, they have come on-board and are also forecasting a landfall in South Carolina four days from now. Certainly, residents of Florida and North Carolina cannot breathe easy yet, until the models portray a more consistent picture of Ophelia's future track.

The intensity forecast, as usual, is highly speculative and low-confidence. The models all show Ophelia strengthening to a Category 1 to Category 3 hurricane by five days from now. The shear that has dogged Ophelia its entire life is forecast to remain, at least in the short term. A weak trough pushing off of the East Coast Saturday may also generate some shear the next few days, as could a large upper-level low over Puerto Rico approaching from the east. Dry air on the north side of the storm may also be a problem for Ophelia. Clearly, there are many hurdles for Ophelia to overcome. That being said, this storm has shown the ability to intensify in the presence of some modest shear, and as she expands in size, will be able to shrug off the shearing winds surrounding her more easily. Ophelia is over warm Gulf Stream waters and will remain so for the next five days. All these factors considered, and given the fact that hurricanes during this unprecedented hurricane season of 2005 have shown an uncanny ability to become intense hurricanes, it would be no surprise if Ophelia grows to a Category 2 or 3 hurricane by early next week.

Elsewhere in the tropics
Maria and Nate are both weakening tropical storms with just a day or two left to live as they move northeast over cold waters. The rest of the tropics are quiet.

Jeff Masters

Updated: 2:55 PM GMT on September 09, 2005

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Hurricane Ophelia likes where she's at

By: JeffMasters, 9:07 PM GMT on September 08, 2005

The Air Force Hurricane Hunters sent in an eye report at 4pm EDT where they observed a central pressure of 985 mb and a surface winds of 70 knots (80 mph). Maximum flight level winds were 66 knots at 5000 feet altitude. This data suggests that Ophelia is at hurricane strength. The maximum temperature in the eye was 5C warmer than just outside the eye, which is a respectable temperature difference typical of a weak Category 1 hurricane. Doppler radar wind estimates also indicate hurricane force winds.


Figure 1. Wind speed estimates from the Melbourne Doppler radar. The dark red color on the south side of the eyewall indicate winds in excess of 64 knots (minimum hurricane force) blowing away from the radar. Because the radar uses the Doppler effect to measure wind speed, it cannot tell what the wind speed is when the winds don't have a component of motion towards or away from the radar, Thus, winds on the east and west eyewall are coded white (a speed of zero towards the radar) and the winds on the north eyewall are coded blue (blowing towards the radar).

Long range radar out of Melbourne FL, shows that a partial eyewall of 15 miles diameter, open to the northeast, has formed. The Hurricane Hunters also confirmed this. Satellite images show improving upper-level outflow in all quadants, and a modest increase in the size of the storm. Outflow and deep convection are still restricted on the southeast side, where strong winds of 10 - 15 knots continue to shear the storm.

No important changes to the environment have occurred or are forecast to occur, and Ophelia should continue to slowly intensify and sit in place the next 24 hours. After that, a slow northeast motion is likely as a weak trough pushes off of the east coast.

Jeff Masters

Updated: 9:08 PM GMT on September 08, 2005

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Ophelia still stuck

By: JeffMasters, 1:19 PM GMT on September 08, 2005

Long range radar out of Melbourne is showing a much more organized and symmetrical echo pattern today. Ophelia's large 50-mile wide center is surrounded on all sides by strong echoes that are slowly increasing in intensity. Satellite imagery shows a lack of deep convection only on the southeast side of the storm, the result of strong upper-level winds shearing the clouds away. This shear has been oscillating up and down the past 36 hours, and is currently between 5 and 10 knots. As long as the shear stays below 10 knots, slow but steady intensification should result. The latest Hurricane Hunter flight at 8:13 am EDT supports this--the pressure has fallen to 988 mb, and surface winds have increased to 60 mph. Ophelia should become a hurricane by tonight or tomorrow morning.

Although Tropical Storm Warnings have been hoisted for the Florida coast, Ophelia seems stuck in place and tropical storm conditions will likely stay just offshore today. Reports from NOAA buoy 41009 located 23 miles east of Cape Canaveral show winds this morning of 30 - 35 knots--just below tropical storm force. The surface wind field from this morning's NOAA Hurricane Hunter flight showed the the winds of the storm were elongated parallel to the coast, with the strongest winds northwest and southeast of the center.


Figure 1. Surface winds measured by the NOAA Hurricane Hunter aircraft's stepped frequency microwave radiometer and other sources this morning.


Doppler radar rain estimates show the heaviest rain is falling just offshore, but this will change this afternoon as the storm continues to intensify, bringing spiral rainbands over Florida that will fire off big thunderstorms. The intense afternoon heating of the ground by the hot Florida sun will contribute towards making these thunderstorms heavy rain producers.


Figure 2.Estimated rainfall from the Melbourne Doppler radar.

OK, it's time to play the "where will Ophelia go?" game. The answer: nowhere soon. Steering currents are very weak, and we can expect Ophelia to remain pretty much where she is now the next three to five days. Of course, since she is so close to the coast, just a slight drift westward would bring tropical storm conditions to the coast. However, the computer models pretty much agree that any motion the next three days is likely to be slowly north and then east. After heading east for a few days, all the models except the GFS agree that Ophelia will eventually loop back and hit the U.S. as a hurricane, perhaps even a major hurricane, seven or more days from now. The GFS takes Ophelia out to sea, but the latest NHC discussion notes that the GFS performed poorly in a similar situation with Hurricane Jeanne last year, and is probably on the wrong page this time around, too.

As far as intensity goes, water vapor satellite images show a large pool of dry air to the northwest of Ophelia. Winds at mid levels of the atmosphere are expected to blow this dry air towards Ophelia the next few days, and this should hamper her development. However, wind shear levels 3 - 5 days from now are expected to drop condsiderably, and this will aid intensification. All factors considered, Ophelia wil probably reach Category 2 status and perhaps Category 3 five days from now.

Hurricane Nate and Hurricane Maria
Nate finally got caught up in the westerly winds aloft sweeping across the North Atlantic, and is headed out to sea. Bermuda will escape with just tropical storm force winds. Maria is still a hurricane but almost dead; NHC will issue its last advisory on this storm later today.

Elsewhere in the tropical
A area of disturbed weather in the southwestern Gulf of Mexico is starting to show signs of organization. This area will have to be watched the next few days, and is likely to only threaten Mexico if it develops. The ITCA is quiet and there is nothing cooking off of the coast of Africa.

Jeff Masters

Updated: 4:11 PM GMT on September 08, 2005

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Ophelia not budging

By: JeffMasters, 9:12 PM GMT on September 07, 2005

Long range radar out of Melbourne this afternoon showed a significant improvement in the organization of Ophelia, and the pressure fell modestly from 999 mb to 996 mb. However, the winds have are still at 50 mph, and Ophelia has not intensified quite as fast as the improved radar presentation would suggest. Upper-level winds over the south side of the system relaxed to the 5 - 10 knot range this morning, but have increased again to about 10 knots. These winds are causing shearing on the south side of Ophelia, and so there is little deep convection there. Ophelia is over warm 29 - 30C water, and no significant increase in the shear is forecast the next 36 hours. This should allow Ophelia to approach hurricane strength by tomorrow night or Friday morning.

I have no additional speculations on her future track. Steering currents are very weak, and there will certainly be plenty of time to speculate on her long-range track the next five days while she wanders within 100 miles of her current location. I don't think Ophelia's winds are strong enough yet to stir up enough cold water and cause weakening. Hurricanes need water of at least 26C to maintain their intensity, and water this warm exists down to a depth of 75 meters over the waters east of Cape Canaveral. Winds of tropical storm force are not strong enough to churn up water from deeper than 75 meters.


Figure 1. Depth in meters of where 26C water can be found.

Jeff Masters

Updated: 9:13 PM GMT on September 07, 2005

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Ophelia--a hurricane tomorrow

By: JeffMasters, 4:17 PM GMT on September 07, 2005

The shear relaxed significantly over Ophelia in the past few hours, and she is now intensifying quickly. The hurricane hunters found a central pressure of 999 mb at 10:50am EDT, a 5 mb drop from seven hours ago. The peak winds of 40 kt (45 mph) on the northwest side are still not too impressive, but these will increase substantially in the next 12 hours, given what the pressure is doing and what I'm seeing on radar.

Long range radar out of Melbourne shows that convection is now starting to wrap all the way around the center, at a rate which is quite impressive. A closed center is likely later this afternoon. This will allow for more rapid intensification, and it now seems likely that Ophelia will be a Category 1 hurricane by tomorrow.

The satellite presentation of Ophelia shows a small storm, with good outflow to the north, and some improving outflow on the south side. The outflow to the north is joining and being aided by the outflow channel on the north side of Hurricane Nate. It will be interesting to see what happens to Ophelia's outflow when Nate scoots off to the northeast tomorrow; my guess is that there will be little effect.

Most of the action has been on the north side of Ophelia, as the northeast coast of Florida can attest to. Nearly three inches of rain has fallen along some coastal areas, from squalls that have rotated in from the ocean. Winds gusts at the St. Augustine pier were as high as 35 - 40 mph overnight. Sustained winds over the ocean areas off shore are 40 - 45 mph, and 12 foot seas have been observed. Large waves from Ophelia are already pounding northern Florida and the Carolinas. Given Ophelia's slow forecast track, this will be a major beach erosion event for these areas. As Ophelia "spins up", the outer rain bands have moved closer to the center of the storm and away from the coast, so Florida and Georgia will get a bit of a break from the rains the remainder of today. By tomorrow, the rains will probably again spread over these areas as Ophelia intensifies and expands in size.


Figure 1. Total rainfall from Ophelia as estimated by the Jacksonville Doppler radar.

The long term track and intensity forecast for Ophelia are highly uncertain. With the storm now intensifying more quickly than anticipated, the models are likely to have some quite different solutions later today. The computer model map has the appearance of a squashed spider, with each model taking Ophelia a different direction. The GFDL and BAMS Medium solutions take Ophelia westward across Florida and into the Gulf of Mexico almost immediately. These solutions are already incorrect, and are being discounted at this time. The Canadian model takes Ophelia out to sea behind Nate, but is the only model calling for this track. What I believe is the most likely scenario is one that is not promising for the U.S. This solution is the one favored by the GFS, UKMET, and NOGAPS models. These models forecast that steering currents over Ophelia will remain weak the next five days, which will allow her to remain over the warm ocean waters and gather strength. A weak trough of low pressure is forecast to move off the east coast Friday, which should act to push Ophelia away from the coast slightly. This trough could also create some shear and dump cold, dry air into the cyclone, weakening it temporarily. However, the GFS, UKMET, and NOGAPS models forecast that this trough will bypass Ophelia, and a ridge of high pressure will build back in forcing Ophelia westward or south-westward back toward the U.S. coast early next week. With so much time over warm water, and the shear likely to decrease once the trough bypasses her, Ophelia will have a good chance of attaining at least Category 2 hurricane status and making landfall somewhere on the Southeast U.S. coast. All interests along the Southeast coast from Miami to Cape Hatteras need to watch this storm.

Nate
Nate is a Category 1 hurricane with a large eye, and should intensify into a Category 2 hurricane by tomorrow. Nate is currently drifting slowly north, but is expected to accelerate norhteastward when the trough currently moving off of the East Coast picks it up tomorrow. This may spell trouble for Bermuda, which has already hoisted a Tropical Storm Warning and a Hurricane Watch.

Maria
Maria was briefly downgraded to a tropical storm, but is now back to a Category 1 hurricane. She is expected to turn into a large and powerful extratropical storm by tomorrow and bring high winds and heavy rain to Iceland on Saturday.

The rest of the tropics
An upper-level low pressure system is over the western Gulf of Mexico and is generating some showers there. There is now some surface low pressure developing underneath, but tropical development in this type of system happens very slowly, and usually not at all.

A large tropical wave with spin just moved off the coast of Africa near 9N, and will have to be watched as it moves westward this week.

Jeff Masters

Updated: 5:41 PM GMT on September 07, 2005

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Ophelia gathering strength

By: JeffMasters, 1:11 PM GMT on September 07, 2005

TD 16 gathered enough strength last night to be given a name--Ophelia. Ophelia will be a name we will hear a lot of over the coming week. She is going to cause plenty of trouble, and will be moving slowly enough that we'll still be talking about her a week from now.

Ophelia is a weak system at present, and is suffering from strong upper-level winds on her south side that are shearing away any convection that tries to develop there. Almost all the action is on the north side of the storm, as the northeast coast of Florida can attest to. Nearly three inches of rain has fallen along some coastal areas, from squalls that have rotated in from the ocean. Winds gusts at the St. Augustine pier were as high as 35 - 40 mph overnight. Sustained winds over the ocean areas off shore are 40 - 45 mph, and 12 foot seas have been observed. Large waves from Ophelia will start to pound the coast from northern Florida to North Carolina over the next five days, creating beach erosion problems. The rains will continue to fall across the north Florida coast, and minor flooding will make driving slow and hazardous by tomorrow in some areas of north Florida.


Figure 1. Total rainfall from Ophelia as estimated by the Jacksonville Doppler radar.

Long range radar out of Melbourne shows a slow increase in intensity and coverage of the rain, and a few spiral bands trying to form on the south side of the storm. Over the next two days, Ophelia should continue to slowly intensify, battling the shear from the strong winds on her southern side. Interference from Nate does not seem to be a problem; the upper-level outflow on Nate's west side has diminished and does not appear to be shearing Ophelia. The ocean has plenty of deep warm water (29 - 30C) under Ophelia, so the intensification potential is high if the shear drops.

The long term track and intensity forecast for Ophelia are highly uncertain. The computer model map has the appearance of a squashed spider, with each model taking Ophelia a different direction. The GFDL and BAMS Medium solutions take Ophelia westward across Florida and into the Gulf of Mexico almost immediately. These solutions are already incorrect, and are being discounted at this time. The Canadian model takes Ophelia out to sea behind Nate, but is the only model calling for this track. What I believe is the most likely scenario is one that is not promising for the U.S., and is favored by the GFS, UKMET, and NOGAPS models. These models forecast that steering currents over Ophelia will remain weak the next two days, which will allow her to remain over the warm ocean waters and slowly gather strength. A weak trough of low pressure is forecast to move off the east coast Friday, which should act to push Ophelia away from the coast slightly. This trough could also create some shear and dump cold, dry air into the cyclone, weakening it temporarily. However, the GFS, UKMET, and NOGAPS models forecast that this trough will bypass Ophelia, and a ridge of high pressure will build back in forcing Ophelia westward or south-westward back toward the U.S. coast. With so much time over warm water, and the shear likely to decrease once the trough bypasses her, Ophelia will have a good chance of attaining at least Category 1 hurricane status and making landfall somewhere on the Southeast U.S. coast. All interests along the Southeast coast from Miami to Cape Hatteras need to watch this storm.

I'll be back early this afternoon with an update, and info on Nate and Maria and the rest of the tropics.

Jeff Masters

Updated: 1:25 PM GMT on September 07, 2005

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TD 16 not too impressive...yet

By: JeffMasters, 7:01 PM GMT on September 06, 2005

The center of Tropical Depression 16 was just fixed by the NOAA hurricane hunters a few miles north of Grand Bahama Island, which is 110 miles east of West Palm Beach, Florida. Peak winds found by the hurricene hunters on the west side were just 20 knots, and the central pressure was a very high 1010 mb. TD 16 is still very disorganized, and is not a threat to intensify rapidly for the next 1 - 2 days.

The peak winds and most intense convection is found well north of the center, in the ocean areas between Cape Canaveral and Jacksonville. QuikSCAT satellite winds of up to 30 - 35 mph exist in this region. The St. Augustine CMAN station reported sustained winds of 37 mph at 1pm EDT, which is only 2 mph below tropical storm force. Daytona Beach has reported heavy rain and winds gusts up to 25 mph in squalls the past few hours.

Melbourne radar shows a large area of echoes circling a very ill-defined center 200 or so miles east of Lake Okeechobee. Doppler radar estimates of the wind velocity from the Miami radar are no longer available, as the Miami radar has failed, and may be down the rest of the day.

As far as intensity goes, TD 16 is in a low shear environment of 5 - 10 knots, and the shear over it is expected to decrease the next two days. I believe that by tomorrow night we will see TD 16 turn into Tropical Storm Ophelia. However, the upper-level ouflow to the northeast of the storm is going to be hampered by the upper level outflow from Tropical Storm Nate. As long as Nate continues to show little movement, TD 16 will suffer and will not be able to intensify very rapidly. By the end of the week, when Nate is expected to move away to the northeast and leave TD 16 behind, more significant strengthening can occur, assuming TD 16 has not made landfall in Florida.

TD 16 should move very slowly the next three days, since it is trapped under a strong high pressure ridge where steering currents are very weak. A slow northward or northwestward motion is indicated by most of the models, which would bring heavy rains to the east coast of Florida all week. The GFDL model, in contrast, moves TD 16 rapidly across Florida and into the Gulf of Mexico. None of the other forecast models show this, and the GFDL solution is being discounted at this time.

Jeff Masters

Updated: 7:03 PM GMT on September 06, 2005

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M, N, O... P?

By: JeffMasters, 1:12 PM GMT on September 06, 2005

The tropics are really cooking now, with activity typical of what sees at the height of a busy hurricane season. We are only in the 4th inning of a 9-inning ball game, and already have our 14th named storm, with the 15th likely on the way! At this rate, the old record of 21 tropical storms set in 1933 will easily be eclipsed, and we'll have to start naming storms using the Greek Alphabet--Alpha, Beta, Gamma, etc. So let's dig in and start discussing the storms, from most important to least important.

Depression developing near Miami
The area of most serious immediate concern is the stationary tropical low centered about 75 miles east of Ft. Lauderdale, FL. This low has increased its deep convection markedly in the past six hours, and appears that a tropical depression will form here later today. The hurricane hunters are scheduled to investigate the system this afternoon.

The best to way to track the storm is on Miami radar. The radar loop shows a large circular ring of strong echoes developing. Doppler radar estimates of the wind velocity from the Miami radar (see image below) show peak winds in the 20 - 26 knot range, which is still below the threshold for a tropical depression (30 kt).


Figure 1. Doppler wind velocities from the Miami radar. The storm to the east of Miami is rotating counter-clockwise, so winds to the northeast of the city blow towards the radar, and winds to the southeast of the city are blowing away from the radar. Wind speeds over the ocean to the northeast of Miami are coded shades of green, meaning winds are blowing at 10 - 26 knots towards the radar (the radar is located in the exact center of the image, and is denoted by a hard-to-see white cross). To the southeast of the radar, the winds are colored yellow to orange, meaning winds are blowing 10 - 26 knots away from the radar. Ignore the echoes over land, most of these echoes are ground clutter. Velocities marked pink (RF) mean that the echoes are too far from the radar for velocities to be determined.

This system should move very slowly the next three days, since it is trapped under a strong high pressure ridge where steering currents are very weak. A slow northward or northwestward motion is indicated by most of the models, which would bring heavy rains to the east coast of Florida starting Wednesday. Most of the models bring the system inland over Central Florida by Thursday as a weak tropical storm and dissipate it. However, some models keep it just off the coast of Florida, and forecast that as the storm tracks further north, it will move more northeasterly away from Florida, following Nate out through a weakness in the ridge. This all depends upon how strong Nate becomes. However, none of the models forecast that the system will follow Nate all the way out to sea. A strong ridge of high pressure is forecast to build in behind Nate and force the system back towards Florida. This system seems destined to spend most of the coming week hanging around Florida. As far as intensity goes, shear levels over the system are 5 - 10 knots, which should allow for some modest strengthening. It is likely we'll have Tropical Storm Ophelia by Thursday. Shear levels are forecast to decrease even lower the next few days, so if the system remains off of the coast of Florida, it has a chance to be a hurricane by the end of the week.


Figure 2. Early forecast model tracks for the developing system east of Ft. Lauderdale.

Tropical Storm Nate
Nate formed last night on the eastern lobe of the same trough of low pressure that spawned the system near Ft. Lauderdale. Remarkably, the GFS forecast from last Thursday correct predicted that two separate storms might emerge from this trough. Nate's satellite signature has improved markedly the past six hours, is over warm waters, and has light shear overhead. We're likely to see Hurricane Nate by Thursday. Nate is moving very slowly, as it is trapped under a strong ridge of high pressure. A trough moving off the east coast Friday should create a weakness in the ridge that will allow Nate to follow Maria out to sea. The only threat from Nate to the U.S. coast will be some high surf that may develop late in the week.

Hurricane Maria
Maria peaked in intensity early this morning, and is now showing significant deterioration thanks to wind shear and cold water. She barely made it to major (Category 3) status last night, with 115 mph winds, the 4th major hurricane of the season. Maria is expected to continue zooming northeastward and turn into a huge and powerful extratropical low that will slam Iceland with high winds and heavy rain on Saturday. Maria's remnants will then weaken, but still bring Norway significant wind and rain on Tuesday.

P?
So, we've talked about M, N, and O, but not P yet. Well, I have no speculations about where the "P" storm might form. My long-range eyes can't see any evidence of other threats in the tropics. The tropical wave that just entered the eastern Caribbean has strong easterly winds at high levels that are shearing it, so that is not a threat. There is a low pressure center off the coast of Africa near 13N 33W, but convection is limited there. The ITCZ is pretty quiet, so for now we just have the M, N, and O storms to worry about.

Dr. Jeff Masters

Updated: 5:52 PM GMT on September 06, 2005

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TD 15? And, Katrina: an unnatural disaster

By: JeffMasters, 2:38 PM GMT on September 05, 2005


Two disturbances to watch off of the coast of Florida
The important threat in the tropics today is a large area of disturbed weather extending from Miami eastward over the Bahama Islands. A small circulation center, visible on winds from the QuikSCAT satellite, has developed in association with this disturbance, about 50 miles east of Ft. Lauderdale, FL. Shear values are still probably a little too high--about 10 knots--to permit a tropical depression to form in this region today. However, the shear is forecast to decrease, and a tropical depression could form Tuesday or Wednesday. The computer models are less agressive developing this system today, but still indicate a tropical storm could form here and very slowly move northwards along the coast of Florida towards the Carolinas.

A second disturbance with a well-defined circulation visible on both visible satellite images and QuikSCAT data is located about 600 miles east of Cape Canaveral, Florida. A concentrated area of deep convection has developed on the south and east sides of the circulation center. There is no convection over the center, which would have to happen before the system can be classified as tropical depression. Highest winds observed by the QuikSCAT satellite are about 20 knots. Shear values are about 10 knots, which is marginal for development, but the shear is likely to decrease some today and tomorrow, and this system has a good chance of becoming Tropical Depression 15. The system is expected to move slowly northwestward and meander in the area between Bermuda and the Carolinas.


Figure 1.Forecast track of tropical low 600 miles east of Cape Canaveral, FL.

African tropical waves
The tropical wave we've been watching cross the Atlantic for the past week is still out there, 300 miles east of the islands. This system has now moved far enough north that it may have a chance to develop later in the week as it moves through the Caribbean Sea.

A huge low pressure system accompanied by a large cloud of Saharan dust moved off of Africa yesterday. The dry air associated with the African dust will inhibit any development of this low.

Hurricane Maria
Hurricane Maria is a pretty sight on satellite images, with a large, well-formed eye. She may continue to intensify and reach Category 3 status by tomorrow as she heads northward and then northeastward out to sea. Expect Maria to die by Friday when cold water and wind shear take their toll.

Jeff Masters

Updated: 12:15 PM GMT on September 06, 2005

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Katrina: an unnatural disaster

By: JeffMasters, 1:17 AM GMT on September 05, 2005

In comments on Thursday, Sep. 1, in an interview with Diane Sawyer of ABC News, President George W. Bush said, "I don't think anybody anticipated the breach of the levees. They did anticipate a serious storm. But these levees got breached."

In comments to the press on Sep. 3, Homeland Security chief Michael Chertoff remarked, "That 'perfect storm' of a combination of catastrophes exceeded the foresight of the planners, and maybe anybody's foresight", and called the disaster "breathtaking in its surprise."

It's not our fault," said Army Lt. Gen. Russel Honore, in charge of the deployment of National Guard troops in New Orleans. "The storm came and flooded the city."

In other words, Katrina was an Act of God no one could have foreseen, and the politicians we elected to protect us from disaster are not responsible for the unimaginable horror we have witnessed this week.

A horror unimagined by anyone, except by every hurricane scientist and government emergency management official for the past forty years and more. It was a certainty that New Orleans would suffer a catastrophe like this. Every 70 years, on average, the central Gulf Coast has a Category 4 or 5 hurricane pass within 80 miles of a given point. Sometimes you get lucky--for a while. New Orleans had gone over 150 years without a strike by a hurricane capable of overwhelming the levees. Sometimes you get unlucky. There's no guarantee that New Orleans won't get hit by another major hurricane this year. We are in the midst of an extraordinary period of hurricane activity, the likes of which has not been seen in recorded history. Hurricanes Ivan and Dennis, which both had storm surges capable of breaching the levees in New Orleans, smashed into Pensacola in the past year. Either of these storms could have destroyed New Orleans, had they taken a slight wobble westward earlier in their track.

Hurricanes are an inescapable part of nature's way on the Gulf Coast. Nature doesn't care about tax cuts and fiscal years and budget crunches. Nature doesn't care that a city of 500,000 people situated below sea level lies in its path. It was certain that New Orleans would sooner or later get hit by a hurricane that would breach the levees. How could the director of Homeland Security not be familiar with this huge threat to the security of this nation? How could the President not know? How could all the presidents and politicians we elected, from Eisenhower to Clinton, not know?

The answer is that they all knew. But the Congressmen we elected and the politicians the citizens of New Orleans and Louisiana elected didn't care about the poor people in New Orleans. Those poor people don't have a lobbyist in Baton Rouge or Washington. Poor people don't make big campaign contributions, and those big campaign contributions are vital to getting elected. In all of the Congressional and Presidential races held over the past ten years, over 90% were won by the candidate that raised the most money.

So there was little effort given to formulate a plan to evacuate the 100,000 poor residents of New Orleans with no transportation of their own for a Category 4 or 5 hurricane. To do so would have cost tens of millions of dollars, money that neither the city, nor the state, nor the federal government was willing to spend. Why spend money that would be wasted on a bunch of poor people? The money was better spent on projects to please the politicians' wealthy campaign contributors. So the plan was to let them die. And they died, as we experts all knew they would. Huge numbers of them. We don't know how many for sure. Since the plan was to let them die, the city of New Orleans made sure they had a good supply of body bags on hand. Only 10,000 body bags, but since Katrina didn't hit New Orleans head-on, 10,000 will probably be enough.

Admittedly, it is very difficult to safely evacuate 100,000 people with a Category 4 or 5 hurricane bearing down on you. There are only a few routes out of the city, and a full 72 hours of warning are needed to get everyone out. That's asking a lot, as hurricanes are very difficult to predict that far in advance. The National Hurricane Center did pretty well, giving New Orleans a full 60 hours to evacuate. The Hurricane Center forecasted on Friday afternoon that Katrina would hit New Orleans as a major hurricane on Monday, which is what happened. New Orleans had time to implement its plan to bus the city's poor out. However, this plan had two very serious problems--it wasn't enacted in time, and it could only get out 20% of the people in a best case scenario.

The mandatory evacuation order was not given until Sunday, just 20 hours before the hurricane. I have not been able to ascertain from press accounts when the busses actually started picking up people. The mayor says 50,000 made it to the Superdome and other "shelters of last resort", leaving another 50,000 to face the flood waters in their homes. Although 80% of the city was evacuated, it is unclear whether any of the city's poor made it out by bus. And it is very fortunate that Katrina did not hit the city head-on, or else most of those in the Superdome and other "shelters of last resort" would have perished. The death toll from Katrina would have easily surpassed 50,000.

Even if the evacuation plan had been launched 72 hours in advance, it almost certainly would have failed. A local New Orleans news station, nola.com, reported in 2002 on the evacuation plan thusly:

In an evacuation, buses would be dispatched along their regular routes throughout the city to pick up people and go to the Superdome, which would be used as a staging area. From there, people would be taken out of the city to shelters to the north.

Some experts familiar with the plans say they won't work.

"That's never going to happen because there's not enough buses in the city," said Charley Ireland, who retired as deputy director of the New Orleans Office of Emergency Preparedness in 2000. "Between the RTA and the school buses, you've got maybe 500 buses, and they hold maybe 40 people
each. It ain't going to happen."

The plan has other potential pitfalls.

No signs are in place to notify the public that the regular bus stops are also the stops for emergency evacuation. In Miami Beach, Fla., every other bus stop sports a huge sign identifying it as a hurricane evacuation stop.

It's also unclear whether the city's entire staff of bus drivers will remain. A union spokesman said that while drivers are aware of the plan, the union contract lacks a provision requiring them to stay.


So, if one does the math, 500 busses times 40 people per bus yields 20,000 people that could have been evacuated in a best-case scenario. Only 20,000 out of 100,000. That isn't a half-hearted effort, it's a one-fifth hearted, criminal effort. We're talking about the lives of 80,000 people or more sacrificed, from a disaster that was certain to happen. By not having a plan to get New Orleans' poor out, the city, state and federal leaders responsible for ensuring the safety of the citizens of New Orleans caused the unbelievable suffering and the needless deaths of thousands of Americans. This was not a natural disaster caused by an act of God, it was an unnatural disaster. In his excellent 2001 book, Acts of God: The Unnatural History of Natural Disaster in America, Ted Steinberg writes: "Calling such events acts of God has long been a way to evade moral responsibility for death and destruction." He shows in the book how countless politicians over the past one hundred years have done their best to evade this moral responsibility when preventable disasters struck. Our current leaders are no different.

The most prosperous and technologically advanced nation in history surely could have done better. Was it really too expensive to have the vehicles, people, and workable plan in place needed to evacuate New Orleans? Yes, the local and state goverments had primary responsibility for the New Orleans evacuation plan, but in an exceptional case like New Orleans, shouldn't the federal government have stepped in with the additional resources needed? "A society is measured by how it treats the weak and vulnerable", said George W. Bush in his State of the Union of Feb 2, 2005. By that measure, the people of this country have responded magnificently. The outpouring of aid, sympathy and prayers for those affected has been tremendous. But by that same standard, our government has failed. Its not just the current administration--every elected government since the days of Eisenhower has failed us. As I've outlined above, the problem is not likely to go away until the amount of money a candidate raises is no longer the primary factor determining who gets elected. Our elected officials won't care for the poor, as long as it is the rich who determine who get elected.

What can we do to help prevent such a disaster from recurring? Well, I encourage all of you to support election reform initiatives such as public campaign financing and Instant Runoff Voting (IRV) over the coming years. Maybe then I can check a box to vote for a candidate who will actually care for the needs of the poor in New Orleans and elsewhere in this county, instead of the usual "lesser of two evils" from the miserable two-party system that let thousands die and tens of thousands more suffer so unbearably.

Dr. Jeff Masters

Updated: 6:00 PM GMT on September 10, 2005

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Tropical development off the coast of Florida

By: JeffMasters, 4:08 PM GMT on September 04, 2005

Two disturbances to watch off of the coast of Florida
The most serious threat in the tropics today is a large area of disturbed weather extending from Miami eastward over the Bahama Islands. Shear values are still probably a little too high--about 10-15 knots--to permit a tropical depression to form in this region today. However, the shear is rapidly decreasing, having fallen 10 knots in the past 24 hours, and is forecast to be 5-10 knots tomorrow. At this level, a tropical depression could form Monday or Tuesday. Several computer models, including the UKMET and NOGAPS, forecast that a strong tropical storm will form here and move slowly northward, threatening the Carolinas late in the week. The GFS model does not develop the system.

A second disturbance with a well-defined circulation visible on both visible satellite images and QuikSCAT data is located about 600 miles east of West Palm Beach, Florida. A concentrated area of deep convection has developed on the south side of the circulation center, and continues to build. Shear values in the region have dropped to 5-10 knots and continue to drop, and the conditions appear favorable for a tropical depression to form by tomorrow. The system is expected to move north and may threaten Bermuda.


Figure 1.Forecast track of tropical low 600 miles east of West Palm Beach, FL.

The Thursday GFS forecast was remarkably accurate--it correctly predicted tropical development in both of these areas, four days in advance!

African tropical waves
The tropical wave we've been watching cross the Atlantic for the past week is still out there, at 10N 53W, 500 miles east of the islands. This system is still too far south to develop significantly, but steering currents should start to push the system just far enough north for it to avoid being destroyed by passage over South America. We will continue to watch this system as it moves westward at 15 mph.

Hurricane Maria
Oh yes, there is a hurricane out there! Maria has a nice looking eye starting to develop, and should be a pretty sight on satellite images the next few days as she heads northward and then northeastward out to sea. Maria should make it to Category 2 and possibly Category 3 status before cold water and wind shear three days from now start taking their toll.

Jeff Masters

Updated: 4:10 PM GMT on September 04, 2005

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No threats in the tropics today

By: JeffMasters, 2:06 PM GMT on September 03, 2005

The new KatrinaBlog

The new KatrinaBlog for all Katrina-related discussions is worth continuing for a few more days. I know it is not an ideal solution and creates some problems for those who wish to communicate about everyting that is going on, but given the volume of posts I think we should continue this separation a while longer. Today, I am featuring a guest blogger on the KatrinaBlog--my wife, who is an emergency physician who will be on her way to the Gulf next week for a two-week shift wherever she's needed. I have also asked another wunderground blogger to assist me in managing and posting to the KatrinaBlog; this blog deserves more time and energy than one person (me) can provide. Again, this is an experiment that may fail, and your feedback is important on judging the success of this effort.

No TD 15
A tropical wave midway between Africa and the Lesser Antilles continues to look unimpressive as it tracks westward at 15 mph. However, the wave is beginning to work its way farther north away from the equator, which might help it get the extra spin needed to develop. We'll have to continue to watch this wave. It could start to develop when it gets closer to the Leeward Islands on Monday or Tuesday, where low wind shear and warm waters should be conducive to develpment.

Development by the Bahamas
Clouds have continued to slowly increase in an area of disturbed weather near and east of the Bahamas. Wind shear is still too high today for a tropical depression to form, but as the wind shear continues to decrease the next few days, something could develop in this region. The latest GFS model run shows that any storm that develops in this area would move slowly, and might push towards the Carolinas.

Tropical Storm Maria
Maria appears on her way to becoming the 5th hurricane of this unbelievable hurricane season. However, we are going to get lucky with this 13th storm of the season. Maria is tracking northward over open ocean, and has little chance of impacting any land areas. For those keeping track, Maria is the earliest 13th named storm ever, beating the record set in 1933, when the 13th tropical storm formed on September 8.
We're not quite halfway though hurricane season yet; historically, the halfway point comes September 10.

Jeff Masters

Updated: 2:11 PM GMT on September 03, 2005

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New KatrinaBlog, and No TD 15!

By: JeffMasters, 4:26 PM GMT on September 02, 2005

New Blog started

Hello all, I have created a new blog titled KatrinaBlog for all Katrina-related discussions. I plan to post all Katrina-related material to both this blog and to my regular JeffMasters blog, but ask you to use the JeffMasters blog for only non-Katrina related subjects. On both blogs, I ask you to keep it positive and use it for discussions. Avoid making posts that more properly belong in a chat room (for example "How are you today?", etc). In the future, we plan to create a multi-threaded blog to allieviate the congestion that has developed on my blog, but that software will take several months to write. Thanks for all the great material many of you have posted, and I'm sorry I haven't had more time to read all your comments and respond directly to many of them!

No TD 15 yet

Yesterday, I was quite concerned about the possibility of a
significant threat developing from a tropical wave spinning midway between Africa and the Leeward Islands, near 8N 35W. This morning, the deep convection around the low has diminished, and Quikscat winds have fallen to about 20 knots surrounding the storm. This tropical wave is not a threat to develop for the next day or two. Why did this wave fall apart? Steering currents pushed the wave somewhat south of due west, bringing the low so close to the equator (latitude 8N) that the low was unable to use the Earth's spin to help it maintain its own spin. The Coriolis Force--that component of the Earth's spin pointing in the vertical direction--is zero at the equator, and a tropical system cannot maintain the spin needed to develop if it ventures too close to the equator, since a portion of the Earth's spin is required. I have never seen a tropical cyclone in the Atlantic spin up south of 8N.

Nevertheless, this wave needs to be watched the next few days as it tracks westward towards the Leeward Islands. When the wave moves a bit further north two or three days from now, the low wind shear and warm waters should be conducive to develpment.

Development by the Bahamas
An area of concentrated clouds has developed east of the Bahamas, but the wind shear is too high here now for any tropical development to occur. However, the shear will decrease over the next few days so that by Sunday or Monday tropical depression could develop in the waters between the Bahamas and Bermuda. This development would occur at the tail end of a cold front that is expected to push off of the East Coast. The latest GFS model run shows that any storm that develops in this area would move slowly, and might take an erratic and unpredictable path.

Tropical Storm Maria
Maria is of little concern. She is a weak system tracking over open ocean, with little chance of impacting any land areas.

Wunderphotographer mudkow60 also happens to be a helicopter pilot rescuing people stranded in Mississippi. He's posted a few amzazing photos below, and adds on one of the captions, "THANKS FOR ALL YOUR RESPONSES. SORRY I HAVE NOT REPLYED.... I AM REALLY BUSY AT WORK.. THANKS."

Remember to post comments about his photos and other Katrina-related material to the KatrinaBlog. It is quite possible that creating a second blog like this won't work; if enough of you find this second blog to be a bad idea, we'll scrap it and go back to the original single blog. Thanks.

Jeff Masters

Updated: 4:43 PM GMT on September 02, 2005

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TD 15? And, New Orleans NWS survives

By: JeffMasters, 10:46 PM GMT on September 01, 2005

The New Orleans NWS office, located in Slidell, LA, was knocked off-line Monday by Katrina as her northern eyewall hammered Slidell and a 15-foot storm surge crashed ashore. The building and radar survived the hurricane, and the staff continues to work there, although all communications remain down. The radar was damaged but is repairable, and a repair team is on the way to work on it. All but one of the employees are accounted for, and the missing employee is assumed to be in a shelter. Meteorologists generally have enough sense to leave evacuation zones, unless of course they are Weather Channel personalities or storm chasers. Most of the employees had their homes destroyed or damaged. A number of satellite phones have arrived at the office, and limited communications are now possible. The Mobile, Alabama NWS office is assuming responsibility for issuing forecasts and warnings for the New Orleans area until full communications can be restored.

Four weather radars in Louisiana, Mississippi, and Florida that were down due to communication infrastructure failures are now back up. Only the Lake Charles, LA radar and New Orleans radar remain down. Communications are still out to the Lake Charles, LA and Jackson, MS NWS offices, and their forecasts and warnings are being issued by other NWS offices until MCI can repair the communications infrastructure. The repair time needed is estimated to be one week.

Tropical update
The most significant threat in the tropics may be from a tropical wave that is spinning midway between Africa and the Leeward Islands, near 9N 36W. This system has gotten much better organized in just the past two hours, and will probably be classified as TD 15 by tomorrow. There is a moderate amount of deep convection near the center, but this is being disrupted some by wind shear. A large area of improving upper-level outflow on the north side and east sides exists, and Quikscat winds are already over 55 mph on the east side. The disturbance is far enough south that it will not get recurved out to sea by the mid-Atlantic trough. The early track models (below) show it moving west-northwest and threatening the Leeward Islands by Tuesday. Virtually all the the computer models forecast the shear over the system to lessen, and develop it into at least a tropical storm. The GFS continues to forecast that this will be a major hurricane. I believe that this will be at least a Category 1 hurricane by Tuesday, and might be trouble for the Leeward Islands.


Figure 1. Forecast track of tropical wave I expect to be TD 15 by Friday.

Development by the Bahamas
An area of concentrated clouds has developed northeast of the Bahamas, but the wind shear is too high here now for any tropical development to occur. However, the shear will decrease over the next few days so that by Sunday or Monday tropical depression could develop in the waters between the Bahamas and Bermuda. This is the same location that Katrina developed. This development would occur at the tail end of a cold front that is expected to push off of the East Coast. The latest GFS model run is showing two possible areas of formation, one near Bermuda, and one near the east coast of Florida. If a depression does form near the east coast of Florida, the likely track would be across Florida and into the Gulf of Mexico. If formation occurs closer to Bermuda, the likely track would be northeastward away from land. I think it is unlikey that two systems would form in the this region; the energy for storm formation will probably concentrate in one area and create one storm. Let's hope that if this occurs, the formation region will be closer to Bermuda and the storm will head out to sea.


Figure 1. GFS forecast for 2am Monday, showing two possible locations a tropical depression may form.

TD Lee and TD 14
Tropical Depression Lee and Tropical Depression 14 are of little concern at this point. Both are weak, sheared systems that are tracking out over open ocean, with little chance of impacting any land areas.

Blog comments
Please continue to post non-weather related comments to this blog for now. In a national emergency like this, it is important for us to communicate freely. Keep it positive! The best way to deal with this unbelievable horror is to be positive and supporting of one another. If you find yourself wanting to make a post that insults another blog poster, please refrain. Criticism of politicians is OK, but remember we elected them!

Jeff Masters

Updated: 10:53 PM GMT on September 01, 2005

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The tropics today

By: JeffMasters, 2:14 PM GMT on September 01, 2005

Just a quick update on the tropics this morning, and I hope to post more on Katrina later today.

The most significant threat in the tropics is the potential on Sunday or Monday for a tropical depression to develop in the waters between the Bahamas and Bermuda. This is the same location that Katrina developed. This development would occur at the tail end of a cold front that is expected to push off of the East Coast. The latest GFS model run is showing two possible areas of formation, one near Bermuda, and one near the east coast of Florida. If a depression does form near the east coast of Florida, the likely track would be across Florida and into the Gulf of Mexico. If formation occurs closer to Bermuda, the likely track would be northeastward away from land. I think it is unlikey that two systems would form in the this region; the energy for storm formation will probably concentrate in one area and create one storm. Let's hope that if this occurs, the formation region will be closer to Bermuda and the storm will head out to sea.


Figure 1. GFS forecast for 2am Monday, showing two possible locations a tropical depression may form.

Tropical Depression Lee is nothing to worry about, it is too far north to have a chance at affecting land, and is suffering from shear that will keep it weak or potentially dissipate it over the next few days. The well-organized wave 1100 miles east of the Lesser Antilles is looking better organized today. The shear over it is relaxing, the dry air on its west side has decreased some, and deep convection is starting to build on the north side. This system will probably become Tropical Depression 14 later today, but its relatively northerly location and northwesterly motion make this system no threat to land. This system will probably recurve out to sea. The most significant threat in the tropicas may be from the tropical wave southwest of the Cape Verdes Islands. This system is far enough south, near latitude 9N, that it will not get recurved out to sea by the mid-Atlantic trough. The tropical wave is currently in a region of strong enough shear that development will not occur, but this shear is expected to relax by Saturday as the wave continues westward over the open Atlantic. As was the case with yesterday's model runs, the GFS forecasts that this wave will become a major hurricane and a potentially threaten the Leeward Islands a week from now.

Updated: 2:41 PM GMT on September 01, 2005

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About

Jeff co-founded the Weather Underground in 1995 while working on his Ph.D. He flew with the NOAA Hurricane Hunters from 1986-1990.

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