Dr. Jeff Masters' WunderBlog

Jelawat hits Okinawa; TS Norman feeds heavy rains in Texas

By: JeffMasters, 5:55 PM GMT on September 29, 2012

Typhoon Jelawat slammed into Okinawa Saturday morning as a Category 3 storm with 115 mph winds. The small 7-mile diameter eye tracked just west of the island from southwest to northeast, bringing the strongest winds of the right-front quadrant eyewall to much of Okinawa. Kadena Air Base recorded sustained 10-minute average winds of 85 mph at the peak of the storm, with a top wind gust of 115 mph. The Kadena Facebook page has some impressive videos and photos of the damage, which included flipped cars, downed trees, and damage to signs and buildings. Satellite loops and radar loops show that Jelawat has weakened considerably. Wind shear is up to a very high 40 knots, and the storm is over much cooler waters. Jelawat is likely to be a tropical storm at landfall Sunday on the main island of Honshu in Japan.


Figure 1. Radar image of Typhoon Jelawat over Okinawa at 12:30 am local time on September 29, 2012. Image credit: Japan Meteorological Agency.


Video 1. Typhoon Jelawat in Okinawa as filmed by storm chaser James Reynolds.

Nadine still a hurricane
Tenacious Hurricane Nadine has entered its 17th day of life, and continues to mill about a few hundred miles southwest of the Azores Islands. Nadine is not expected to be a threat to any land areas for the next five days. The latest model runs show Nadine becoming tangled up with an upper level low pressure system on Wednesday and Thursday as the storm comes close to the Azores Islands. This should cause Nadine to become an extratropical cyclone again. Nadine is already in fourth place for longest-lived named tropical storm since 1950:

1) Ginger, 1971: 21.25 named storm days
2) Carrie, 1957: 19.5 named storm days
3) Alberto, 2000: 19.25 named storm days
4) Nadine, 2012: 17.0 named storm days

The all-time record is held by the San Ciriaco Hurricane of 1899, which had 28 named storm days.


Figure 2. MODIS satellite image of Hurricane Nadine taken at 9:12 am EDT Saturday, September 29, 2012. At the time, Nadine had top winds of 75 mph. Image credit: Navy Research Lab, Monterey.

Tropical Depression Norman dying; heavy rains continue over Texas
Tropical Depression Norman has been moving slowly up the Gulf of California near the tip of Baja, Mexico since it formed Friday afternoon, but has been torn apart by high wind shear of 20 - 30 knots. The storm will likely be declared dead later today. Moisture from Norman fed an extratropical storm over Texas, and contributed to heavy rains in West Texas that caused flooding and water rescues on Friday. Midland-Odessa, Texas, picked up 4.66” of rain on Friday, making it the wettest September day on record and 3rd wettest day in city history (wettest day in city history: August 24th, 1934, when 5.32” fell.)


Figure 3. Tropical Storm Norman in the Gulf of California at 4:30 pm EDT Friday, September 29, 2012. At the time, Norman had top winds of 40 mph, and was spreading a large stream of moisture northeastward into Mexico and Texas. The remains of Hurricane Miriam are at the left of the image, along with a curious little vortex just north of Miriam's remains. Image credit: NASA/GSFC.


Figure 4. Radar-estimated rainfall in West Texas due to the moisture associated with Tropical Storm Norman. Heavy rains in excess of 4" fell near Midland/Odessa, Big Spring, and San Angelo.


Figure 5. Predicted rainfall totals for the 5-day period ending at 8 am EDT Thursday, October 4, 2012. Moisture from the Eastern Pacific's Tropical Storm Norman will bring heavy rains to much of the South. Image credit: NOAA/Hydrometeorological Prediction Center.

I'll have a new post on Monday.

Jeff Masters

Hurricane

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A Jelawat mystery; moisture associated with TS Norman drenching Texas

By: JeffMasters, 3:45 PM GMT on September 28, 2012

Powerful Typhoon Jelawat is hammering Japan's Ryukyu Islands as the typhoon steams northeastwards towards Okinawa at 12 mph. Jelawat has weakened to a Category 3 storm with 125 mph winds, thanks to an eyewall replacement cycle and an increase in wind shear to a high 20 - 30 knots. At 7 pm local time, the winds today at Shimoji Shima Island were 66 mph, gusting to 85 mph. Jelawat has dumped 308.5 mm (12.1") rain in 12 hours at Tarama Airport. Satellite loops and radar loops show an impressive, well-organized typhoon with a 33 mile-wide eye, and a large, symmetric area of heavy thunderstorms with cold cloud tops.

The models are in close agreement that Jelawat will pass over or very close to Okinawa, Japan, as a Category 2 or 3 typhoon on Saturday, between 03 - 06 UTC. Jelawat could hit the main island of Honshu in Japan as a tropical storm or Category 1 typhoon on Sunday. Wind shear will continue to increase over Jelawat for the remainder of its life, causing a steady weakening of the storm.


Figure 1. Radar image of Typhoon Jelawat over Japan's southern Ryukyu Islands at 11:05 pm local time on September 28, 2012. Image credit: Japan Meteorological Agency.

A Jelawat mystery
Jelawat has had a classic appearance on satellite imagery during its long stint as a Super Typhoon, with a large symmetric eye surrounded by intense thunderstorms with very cold cloud tops. However, at two points in its life--for several hours on September 25 (Figure 2), and again near 08 UTC September 27--both visible and infrared satellite images showed a very odd boundary extending north-northwestwards from the northeast side of the eye for about 50 miles. I've never seen any such feature in a tropical cyclone, and am a loss to explain what is going on. The typhoon was not close enough to any land areas for this to be a topographic effect, and there wasn't any obvious dry air or significant wind shear that could have caused a perturbation like this.


Figure 2. High resolution visible (left) and infrared (right) satellite imagery of Super Typhoon Jelawat from the new Suomi VIIRS instrument, taken at 0431 UTC on September 25, 2012. At the time, Jelawat was a Category 5 storm with 160 mph winds. A very odd line appears along the north side of the eye. Image credit: Dan Lindsey, Colorado State University.
Brian Tang

Nadine a hurricane again
Non-stop Nadine has regenerated to hurricane strength again, as the long-lived storm enters its 16th day of life. Nadine is not expected to be a threat to any land areas for the next seven days, but moisture associated with Nadine has flowed eastwards over Spain, bringing heavy rains and flooding problems. The GFS model shows Nadine getting caught up in a trough of low pressure on Wednesday and lifted to the northeast over colder waters, where it would likely die. The 00Z run of the ECMWF model predicts that Nadine will hang around an extra two days, finally getting pulled northeastward over cold waters next Friday. Nadine is already in eighth place for longest-lived named storm since 1950, according to a list compiled by Dr. Phil Klotzbach of Colorado State University:

1) Ginger, 1971: 21.25 named storm days
2) Carrie, 1957: 19.5 named storm days
3) Alberto, 2000: 19.25 named storm days
4) Bertha, 2008: 17 named storm days
5) Inga, 1969: 17 named storm days
6) Kyle, 2002: 16.75 named storm days
7) Inez, 1966: 16.25 named storm days
8) Nadine, 2012: 16.0 named storm days

The all-time record is held by the San Ciriaco Hurricane of 1899, which had 28 named storm days.


Figure 3. MODIS satellite image of Tropical Storm Nadine taken at 8:30 am EDT Friday, September 28, 2012. At the time, Nadine had top winds of 70 mph, and would be declared a hurricane 3 hours later. Image credit: Navy Research Lab, Monterey.

Tropical Storm Norman forms near Baja, Mexico; associated moisture feeding heavy rains in Texas
Tropical Storm Norman has formed this morning near the tip of Baja, Mexico, and promises to be a potent rain-maker for Mexico and the Southern U.S. Norman's moisture will feed the formation of an extratropical storm that will form in South Texas on Saturday. The storm's center will potentially move over the Northern Gulf of Mexico on Sunday and Monday, but the storm will probably not have enough time over water to convert to a tropical system. The storm will bring heavy flooding rains to Texas, Louisiana, Mississippi, Alabama, and the Florida Panhandle Saturday through Monday. Flooding has already been observed in West Texas this morning. Midland-Odessa picked up 3.12” of rain so far today, making it the 3rd wettest September day on record. The wettest day in city history is August 24th, 1934, when 5.32” fell.


Figure 4. Predicted rainfall totals for the 5-day period ending at 8 am EDT Wednesday, October 3, 2012. Moisture from the Eastern Pacific's Tropical Storm Norman is expected to surge eastwards and bring heavy rains to much of Texas and the North Gulf Coast. Image credit: NOAA/Hydrometeorological Prediction Center.

New African wave may develop next week
A tropical wave expected to move off the coast of Africa on Sunday will develop into a tropical depression by next Wednesday, predicts today's 06Z run of the NOGAPS model. The wave is predicted to recurve to the north more than 1,000 miles east of the Lesser Antilles Islands.

Jeff Masters

Hurricane

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Jelawat brushing Taiwan; Nadine enters its 15th day of life

By: JeffMasters, 2:50 PM GMT on September 27, 2012

Impressive Super Typhoon Jelawat remains just below Category 5 strength, as it heads north-northwest a few hundred miles east-southeast of Taiwan. The outer rain bands of the mighty typhoon are bringing heavy rains to the northern portion of the Philippines' Luzon Island, and will spread over eastern Taiwan later today, as seen on Taiwan radar. Wind shear remains a light 5 - 10 knots over Jelawat, and the typhoon is over very warm ocean waters of 29°C. These warm waters do not extend to as great depth as they did when Jelawat was east of the Philippines, though. Satellite loops show an impressive, well-organized typhoon with a 43 mile-wide eye, and a large, symmetric area of heavy thunderstorms with cold cloud tops.

The models are fairly unified on the track of Jelawat. The typhoon is expected to move north-northwest and then north, with the center passing about 150 miles to the east of Taiwan on Friday. Jelawat will likely pass very close to Okinawa, Japan as a Category 2 or 3 typhoon on Saturday, between 03 - 06 UTC. Jelawat could hit the main island of Honshu in Japan as a tropical storm on Sunday. Wind shear will begin increasing over Jelawat beginning on Friday morning, which should cause a steady weakening of the storm.


Figure 1. MODIS satellite image of Super Typhoon Jelawat taken at 1:03 am EDT Thursday, September 27, 2012. At the time, Jelawat had top winds of 155 mph, and an unusually large 43-mile diameter eye. Image credit: Navy Research Lab, Monterey.


Figure 2. Super Typhoon Jelawat's rain bands approaching Taiwan at 22:20 local time on September 27, 2012. Image credit: Central Weather Bureau, Taiwan.

Nadine enters its 15th day of life
The Energizer-bunny storm of 2012, Tropical Storm Nadine, has entered its 15th day of life as a tropical cyclone. Nadine may circle back to bother the Azores Islands on Tuesday, according to the latest run of the GFS model. That model shows Nadine getting caught up in a trough of low pressure by Wednesday and lifted to the northeast over colder waters, where it would likely die late next week. However, the 00Z run of the ECMWF model predicts that Nadine will miss the trough, and meander in the Central Atlantic for at least the next ten days. Nadine is already in ninth place for longest-lived named storm since 1950, according to a list compiled by Dr. Phil Klotzbach of Colorado State University:

1) Ginger, 1971: 21.25 named storm days
2) Carrie, 1957: 19.5 named storm days
3) Alberto, 2000: 19.25 named storm days
4) Bertha, 2008: 17 named storm days
5) Inga, 1969: 17 named storm days
6) Kyle, 202: 16.75 named storm days
7) Inez, 1966: 16.25 named storm days
8) Faith, 1966: 15.5 named storm days
9) Nadine, 2012: 15.0 named storm days

The all-time record is held by the San Ciriaco Hurricane of 1899, which had 28 named storm days.


Figure 2. MODIS satellite image of Tropical Storm Nadine taken at 10:15 am EDT Wednesday, September 26, 2012. At the time, Nadine had top winds of 50 mph. Image credit: NASA.

The rest of the Atlantic is quiet
None of the reliable computer models is predicting tropical cyclone development in the Atlantic through October 3. Most of the models predict that an extratropical storm will form in the Gulf of Mexico on Sunday, off the coast of Texas. Phase Space Diagrams from Florida State University show that this low is expected to remain non-tropical as it moves east-northeast across the Gulf, potentially coming ashore over the Florida Panhandle on Tuesday.

Jeff Masters

Hurricane

Updated: 1:15 PM GMT on September 28, 2012

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Super Typhoon Jelawat headed towards Okinawa

By: JeffMasters, 2:23 PM GMT on September 26, 2012

Super Typhoon Jelawat completed an eyewall replacement cycle over the past 24 hours, resulting in a slight weakening of the storm below Category 5 strength. Jelawat is now a Category 4 super typhoon with 155 mph winds. Fortunately, Jelawat is located well east of the Philippine Islands, and the storm is not expected to hit land while it is at major typhoon strength. Wind shear remains a light 5 - 10 knots over Jelawat, and the typhoon is over very warm ocean waters of 29°C that extend to great depth, so it is possible that Jelawat could regain Category 5 status later today. Satellite loops show an impressive, well-organized typhoon with a 25 mile-wide eye, and a large, symmetric area of heavy thunderstorms with cold cloud tops.

The models are fairly unified on the track of Jelawat. The typhoon is expected to move northwest, roughly parallel to the Philippines, then turn to the north and north-northeast a few hundred miles east of Taiwan. Jelawat will likely pass close to Okinawa, Japan as a Category 2 typhoon on Friday near 20 UTC, and could hit the main island of Honshu in Japan as a tropical storm over the weekend. Wind shear will begin increasing over Jelawat beginning on Thursday, which should cause a steady weakening of the storm.


Figure 1. Microwave satellite image of Jelawat taken at 7:12 am EDT Tuesday September 26, 2012. A solid ring of echoes surrounds the calm eye. Image credit: Navy Research Lab, Monterey.

Tropical Storm Miriam steadily weakening
In the Eastern Pacific, Tropical Storm Miriam is being attacked by high wind shear of 20 - 25 knots, and satellite imagery shows the storm is falling apart. High wind shear in excess of 30 knots will attack Miriam by Thursday, and Miriam should dissipate off the coast of Baja by Friday. Miriam's moisture is expected to stay out to sea.


Figure 2. MODIS satellite image of Tropical Storm Nadine taken at 11:15 am EDT Monday September 25, 2012. At the time, Nadine had top winds of 45 mph. Image credit: NASA.

Except for Nadine, the Atlantic is quiet
Never-say-die Tropical Storm Nadine continues to wander in the middle of the Atlantic Ocean, far from any land areas. Nadine may circle back to bother the Azores Islands on Monday, according to the latest run of the GFS model--though the model shows Nadine stopping short of a direct hit on the islands. Nadine has already been around as a named storm for thirteen days, and will still probably be around a week from now. According to the Tropical Cyclone FAQ, the average Atlantic named storm lasts about six days, and the all-time longest-lived Atlantic tropical cyclone lasted 27.75 days.

A small area of heavy thunderstorms has developed about 700 miles east-northeast of the northern Lesser Antilles Islands. This disturbance is under a high 20 - 30 knots of wind shear, is struggling with dry air, and none of the reliable computer models are predicting development. In their 8 am Tropical Weather Outlook, NHC gave the disturbance a 10% chance of developing into a tropical cyclone by Wednesday.

Jeff Masters

Hurricane

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Earth's second Cat 5 of 2012: Super Typhoon Jelawat

By: JeffMasters, 12:05 PM GMT on September 25, 2012

Earth's newest addition to the Category 5 tropical cyclone club is Super Typhoon Jelawat, which has intensified to a Category 5 typhoon with 160 mph winds. Jelawat is Earth's second Category 5 storm of 2012; the other was Super Typhoon Sanba (175 mph winds), which hit Okinawa earlier this month as a Category 3 storm. The two Category 5 storms for 2012 match the total from all of last year. Fortunately, Jelawat is located well east of the Philippine Islands, and the storm is not expected to hit land over the next two days. However, the storm's outer spiral bands have brought flooding to Zamboanga del Norte province in the eastern Philippines, where 8400 people were evacuated and one person is missing. Wind shear is a light 5 - 10 knots over Jelawat, and the typhoon is over very warm ocean waters of 29°C. These warm waters extend to great depth, which should allow Jelawat to maintain major typhoon status for at least two more days. Satellite loops show an impressive, well-organized typhoon with a large symmetric area of heavy thunderstorms with cold cloud tops.

The models have come into much better agreement on the track of Jelawat over the next three days. The typhoon is expected to move slowly to the north-northwest to northwest, roughly parallel to the Philippines, then turn to the north a few hundred miles east of Taiwan. After that, there remains major uncertainty on where Jelawat might go. A northerly path towards Okinawa or a more northeasterly path out to sea are the two main possibilities. Wind shear will begin increasing over Jelawat beginning on Wednesday, which should cause a steady weakening of the storm.



Figure 1. MODIS satellite image of Jelawat taken at 10:10 pm EDT Monday, September 24, 2012. At the time, Jelawat was a Category 5 storm with 160 mph winds. Image credit: NASA.

Hurricane Miriam off the Baja coast now a Cat 2
Hurricane Miriam completed an eyewall replacement cycle this morning, which knocked down the storm to Category 2 strength with 105 mph winds. Satellite imagery shows that Miriam now has a large 35-mile diameter eye, and the storm has a more ragged appearance than when it peaked as a Category 3 storm with 120 mph winds on Monday. High wind shear in excess of 30 knots will attack Miriam late this week, and our two top models, the GFS and ECMWF, show Miriam dissipating before reaching central Baja on Friday.


Figure 2. Hurricane Miriam as seen by the MODIS instrument on NASA's Aqua satellite at 5pm EDT September 24, 2012. At the time, Miriam was a Category 3 hurricane with 120 mph winds. Image credit: NASA.

Persistent Nadine still out there
The Atlantic's perpetual tropical storm, Nadine, continues to wander in the Middle Atlantic, far from any land areas. Nadine will still probably be around a week from now, and is not likely to threaten any land areas for at least the next seven days. None of the reliable computer models are predicting formation of a new tropical cyclone in the Atlantic for the remainder of the week.

Jeff Masters

Hurricane

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Miriam Hits Cat 3 Strength off of Mexico; Jelawat a Cat 4 Super Typhoon

By: JeffMasters, 3:17 PM GMT on September 24, 2012

In the Eastern Pacific off the coast of Baja Mexico, Hurricane Miriam put on a burst of rapid intensification this morning that has brought it to Category 3 strength with 120 mph winds. This makes Miriam the 2nd strongest Eastern Pacific hurricane of 2012 behind Hurricane Emelia of July, which hit Category 4 strength with 140 mph winds. Satellite imagery shows that Miriam has a tiny "pinhole" eye, and continues to intensify. Miriam could approach Category 4 strength before an eyewall replacement cycle begins early Tuesday. High wind shear will attack Miriam late this week, and our two top models, the GFS and ECMWF, show Miriam hitting central Baja as a weak tropical storm on Friday or Saturday, with moisture from the storm streaming into Arizona and New Mexico by Sunday.


Figure 1. Morning satellite image of Hurricane Miriam.

Super Typhoon Jelawat the 2nd strongest tropical cyclone of 2012
In the Western Pacific, Super Typhoon Jelawat put on a remarkable burst of rapid intensification on Sunday, strengthening from a tropical storm with 65 mph winds to a Category 4 typhoon with 140 mph winds in just 24 hours. Jelawat has topped out as a Category 4 super typhoon with 150 mph winds, making it the 2nd strongest tropical cyclone on Earth so far in 2012, behind Super Typhoon Sanba (175 mph winds.) Jelawat is located about 200 miles to the east of the Philippine Islands, and the storm's outer spiral bands are bringing some moderate rains to the eastern Philippines. Wind shear is a light 5 - 10 knots, and Jelawat is over very warm ocean waters of 29°C. These warm waters extend to great depth, resulting in a total ocean heat content of over 100 KJ/cm^2, which is exceptionally high. These conditions should allow Jelawat to maintain major typhoon status for at least three more days. Satellite loops show an impressive, well-organized typhoon with a large symmetric area of heavy thunderstorms with cold cloud tops.

Jelawat is expected to move slowly to the north-northwest to northwest, roughly parallel to the Philippines, through Tuesday. After that, there remains major uncertainty on where Jelawat might go, with the spread in the computer models about 400 miles for the 3-day forecast. The official Joint Typhoon Warning Center forecast compromises between the unusually large spread in the models, predicting a path well east of the Philippines and Taiwan. However, our two top models--the GFS and ECMWF--both predict that Jelawat will hit Taiwan, and the ECMWF model predicts that Jelawat will also graze the northern portion of the Philippines' Luzon Island. Given the large spread in models, the 3 - 5 day forecast for Jelawat is low-confidence, and residents of Luzon and Taiwan should not assume that Jelawat will miss them.


Figure 2. MODIS satellite image of Jelawat taken at 12:30 am EDT Monday, September 24, 2012. At the time, Jelawat was a Category 4 storm with 145 mph winds. Image credit: NASA.

Pesky Nadine still out there
Persistent Tropical Storm Nadine continues to wander westwards in the Middle Atlantic, far enough south of the Azores Islands that those islands will see only very sporadic rain showers over the next few days. Nadine will likely turn to the north over the middle Atlantic late this week, but will still probably be around a week from now. The storm is not likely to threaten any land areas for at least the next seven days.

GOES-13 satellite outage
The imaging instrument on NOAA's geostationary satellite that provides regular images every 15 minutes for the Eastern U.S. and Atlantic Ocean, GOES-13, has been experiencing an increasing amount of noise in the signal since September 12. The noise got so bad on Sunday night that the instrument was placed in stand-by mode, and engineers are attempting to troubleshoot the problem. GOES-15, the geostationary satellite that covers the Western U.S. and Eastern Pacific, is now taking images of all of North America to help compensate. However, there is no regular 15-minute satellite imagery available for most of the North Atlantic, including the Caribbean. September is a bad time to be without satellite imagery over the Atlantic, but fortunately, there are not any threat areas in the Atlantic we are currently worried about. The CIMSS Satellite Blog has more information on the outage, and also has links to polar orbiting satellite imagery over the region where we do not have geostationary data. The loss of GOES-13 data will degrade the accuracy of the computer forecast models for the globe, particularly over the Atlantic, for the duration of the outage.

Jeff Masters

Hurricane

Updated: 3:19 PM GMT on September 24, 2012

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Nadine is back; Jelawat explodes into a Category 4 typhoon

By: JeffMasters, 4:39 PM GMT on September 23, 2012

Tropical Storm Nadine is back, like a nasty cold you just can't get rid of. Nadine had moved southeastwards over cool waters on Friday and Saturday, which robbed the storm of its heavy thunderstorms and tropical characteristics. But Nadine wandered back to the west this Sunday morning over slightly warmer waters, allowing the storm to regain its heavy thunderstorms and its name. Steering currents favor a continued westwards motion for Nadine, keeping the storm far enough south of the Azores Islands that they will see only very sporadic rain showers over the next few days. Nadine will likely turn to the north over the middle Atlantic late this week, but will still probably be around a week from now. The storm is not likely to threaten any land areas for at least the next seven days.


Figure 1. True-color MODIS satellite image of Tropical Storm Nadine, taken at 9:50 am EDT Sunday, September 23, 2012. At the time, Nadine had top winds of 60 mph. Image credit: NASA.

Typhoon Jelawat explodes into a Category 4 storm
In the Western Pacific, Typhoon Jelawat put on a remarkable burst of rapid intensification, strengthening from a tropical storm with 65 mph winds to a Category 4 typhoon with 140 mph winds in just 24 hours. Jelawat is located about 200 miles to the east of the Philippine Islands, and the storm's outer spiral bands are bringing moderate rains to the eastern Philippines. Jelawat is expected to move slowly to the north-northwest to northwest, roughly parallel to the Philippines, through Tuesday. The predicted path is far enough from the Philippines to spare the islands the kind of torrential rains capable of causing major flooding. Wind shear is a light 5 - 10 knots, and Jelawat is over very warm ocean waters of 29°C. These warm waters extend to great depth, resulting in a total ocean heat content of over 100 KJ/cm^2, which is exceptionally high. These favorable conditions for intensification have prompted the Joint Typhoon Warning Center to predict that Jelawat will become a Category 5 typhoon by Monday. Satellite loops show an impressive, well-organzied typhoon with a large symmetric area of heavy thunderstorms with cold cloud tops. There remains a huge uncertainty on where Jelawat might go. The computer models fall into two distinct camps, 350 miles apart, for Jelawat's 3-day position. The models are even more divergent--700 miles apart--for the storm's 5-day position. The more westward solution provided by our two top models, the ECMWF and GFS, is the one currently depicted in the official Joint Typhoon Warning Center forecast. Given the large spread in models, the 3 - 5 day forecast for Jelawat is low-confidence.


Figure 2. Visible satellite image of Jelawat taken at 4:32 am EDT Sunday, September 23, 2012. Image credit: NOAA.

Tropical Storm Miriam in the Eastern Pacific growing more organized
In the Eastern Pacific, Tropical Storm Miriam appears poised to put on a burst of rapid intensification that would make it a hurricane on Monday. Our two top models, the GFS and ECMWF, are divergent in their long-range predictions for Miriam. The GFS shows Miriam hitting central Baja on Friday, while the ECMWF keeps the storm offshore, dissipating it a few hundred miles off the Baja coast.

Jeff Masters

Hurricane

Updated: 1:33 PM GMT on September 24, 2012

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Nadine goes extratropical; the Atlantic is quiet

By: JeffMasters, 4:46 PM GMT on September 22, 2012

For the first day since August 20, the National Hurricane Center is not issuing advisories on an active tropical cyclone in the Atlantic. On Friday, Tropical Storm Nadine finally transitioned to an extratropical storm, due to cool waters and the influence of an upper-level low. The final fate of Nadine is very uncertain; the extratropical version of Nadine is expected to meander between the Azores Islands and Europe for at least a week, and could potentially become a tropical storm again. In their 8 am EDT Tropical Weather Outlook, NHC gave the ex-Nadine a 40% chance of becoming a subtropical or tropical cyclone by Monday morning.

We've been in a relatively quiet period in the Atlantic for over a week now, and the computer models predict that this quiet period will last at least another week. The quiet period is primarily due to the fact that the African Monsoon has been less active, and there are fewer tropical waves coming off the coast of Africa. Even the busiest hurricane season has quiet periods like this, and we should not assume that hurricane season is over. The first two weeks of October are typically a busy period for tropical cyclones in the Atlantic, and I expect that we'll see one or two more names storms in the Atlantic before October 15.


Figure 1. True-color MODIS satellite image of Ex-Tropical Storm Nadine, taken at 9:05 am EDT Saturday, September 22, 2012. Image credit: NASA.

Tropical Storm Jelawat a threat to the Philippine Islands
In the Western Pacific, Tropical Storm Jelawat threatens to become the most dangerous typhoon of the year for the Philippine Islands. Jelawat is located about 200 miles to the east of the islands, and is expected to move slowly to the northwest, roughly parallel to the Philippines, through Tuesday. Wind shear is moderate 5 - 15 knots, and Jelawat is over very warm ocean waters of 29°C. These warm waters extend to great depth, resulting in a total ocean heat content of over 100 KJ/cm^2, which is exceptionally high. These favorable conditions for intensification have prompted the Joint Typhoon Warning Center to predict that Jelawat will become a Category 4 typhoon by Tuesday. Satellite loops show that Jelawat is becoming more organized, with a large symmetric area of heavy thunderstorms with cold cloud tops. The long-range path of Jelawat is very uncertain; the 00Z ECMWF model takes the storm over the northern end of Luzon Island in the Philippines on Wednesday, while the latest 12Z run of the GFS model keep the storm several hundred miles east of the Philippines through Wednesday.


Figure 2. IR satellite image of Jelawat taken at 12:30 pm EDT Saturday, September 22, 2012.

I'll have a new post on Monday at the latest. Happy first day of fall!

Jeff Masters

Hurricane

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Earth's attic is on fire: Arctic sea ice bottoms out at a new record low

By: JeffMasters, 3:46 PM GMT on September 20, 2012

The extraordinary decline in Arctic sea ice during 2012 is finally over. Sea ice extent bottomed out on September 16, announced scientists at the National Snow and Ice Data Center (NSIDC) on Wednesday. The sea ice extent fell to 3.41 million square kilometers, breaking the previous all-time low set in 2007 by 18%--despite the fact that this year's weather was cloudier and cooler than in 2007. Nearly half (49%) of the icecap was gone during this year's minimum, compared to the average minimum for the years 1979 - 2000. This is an area approximately 43% of the size of the Contiguous United States. And, for the fifth consecutive year--and fifth time in recorded history--ice-free navigation was possible in the Arctic along the coast of Canada (the Northwest Passage), and along the coast of Russia (the Northeast Passage or Northern Sea Route.) "We are now in uncharted territory," said NSIDC Director Mark Serreze. "While we've long known that as the planet warms up, changes would be seen first and be most pronounced in the Arctic, few of us were prepared for how rapidly the changes would actually occur. While lots of people talk about opening of the Northwest Passage through the Canadian Arctic islands and the Northern Sea Route along the Russian coast, twenty years from now from now in August you might be able to take a ship right across the Arctic Ocean."


Figure 1. Arctic sea ice reached its minimum on September 16, 2012, and was at its lowest extent since satellite records began in 1979. Image credit: National Snow and Ice Data Center (NSIDC).

When was the last time the Arctic was this ice-free?
We can be confident that the Arctic did not see the kind of melting observed in 2012 going back over a century, as we have detailed ice edge records from ships (Walsh and Chapman, 2001). It is very unlikely the Northwest Passage was open between 1497 and 1900, since this spanned a cold period in the northern latitudes known as "The Little Ice Age". Ships periodically attempted the Passage and were foiled during this period. Research by Kinnard et al. (2011) shows that the Arctic ice melt in the past few decades is unprecedented for at least the past 1,450 years. We may have to go back to at least 4,000 B.C. to find the last time so little summer ice was present in the Arctic. Funder and Kjaer (2007) found extensive systems of wave generated beach ridges along the North Greenland coast, which suggested the Arctic Ocean was ice-free in the summer for over 1,000 years between 6,000 - 8,500 years ago, when Earth's orbital variations brought more sunlight to the Arctic in summer than at present. Prior to that, the next likely time was during the last inter-glacial period, 120,000 years ago. Arctic temperatures then were 2 - 3°C higher than present-day temperatures, and sea levels were 4 - 6 meters higher.


Figure 2. Year-averaged and 3-month averaged Northern Hemisphere sea ice extent from Chapman and Walsh (2001), as updated by the University of Illinois Cryosphere Today. I've updated their graph to include 2011 plus the first 9 months of 2012.


Figure 3. Late summer Arctic sea ice extent over the past 1,450 years reconstructed from proxy data by Kinnard et al.'s 2011 paper, Reconstructed changes in Arctic sea ice over the past 1,450 years. The solid pink line is a smoothed 40-year average, and the light pink areas shows a 95% confidence interval.  Note that the modern observational data in this figure extend through 2008, though the extent is not as low as the current annual data due to the 40-year smoothing. More commentary on this graph is available at skepticalscience.com.

When will the Arctic be ice-free in summer?
So, when will Santa's Workshop need to be retrofitted with pontoons to avoid sinking to the bottom of the Arctic Ocean in summer? It's hard to say, since there is a large amount of natural variability in Arctic weather patterns. Day et al. (2012) found that 5 to 31% of the changes in Arctic sea ice could be due to natural causes. However, the sea ice at the summer minimum has been declining at a rate of 12% per decade, far in excess of the worst-case scenario predicted in the 2007 IPCC report. Forecasts of an ice-free Arctic range from 20 - 30 years from now to much sooner. Just this week, Dr. Peter Wadhams of Cambridge University predicted that the Arctic will be ice-free in summer within four years. A study by Stroeve et al. (2012), using the updated models being run for the 2014 IPCC report, found that "a seasonally ice-free Arctic Ocean within the next few decades is a distinct possibility." Of the 21 models considered, 2022 was the earliest date that complete Arctic sea ice occurred in September.


Video 1. A powerful storm wreaked havoc on the Arctic sea ice cover in August 2012. This visualization shows the strength and direction of the winds and their impact on the ice: the red vectors represent the fastest winds, while blue vectors stand for slower winds. According to NSIDC, the storm sped up the loss of the thin ice that appears to have been already on the verge of melting completely.Video credit: NASA.

But Antarctic sea ice is growing!
It's a sure thing that when Arctic sea ice hits new record lows, global warming contrarians will attempt to draw attention away from the Arctic by talking about sea ice around Antarctica. A case in point is an article that appeared in Forbes on Wednesday by James Taylor. Mr. Taylor wrote, "Antarctic sea ice set another record this past week, with the most amount of ice ever recorded on day 256 of the calendar year (September 12 of this leap year)...Amusingly, page after page of Google News results for Antarctic sea ice record show links to news articles breathlessly spreading fear and warning of calamity because Arctic sea ice recently set a 33-year low. Sea ice around one pole is shrinking while sea ice around another pole is growing. This sure sounds like a global warming crisis to me."

This analysis is highly misleading, as it ignores the fact that Antarctica has actually been warming in recent years. In fact, the oceans surrounding Antarctica have warmed faster than the global trend, and there has been accelerated melting of ocean-terminating Antarctic glaciers in recent years as a result of warmer waters eating away the glaciers. There is great concern among scientists about the stability of two glaciers in West Antarctica (the Pine Island and Thwaites Glaciers) due the increase in ocean temperatures. These glaciers may suffer rapid retreats that will contribute significantly to global sea level rise.

Despite the warming going on in Antarctica, there has been a modest long-term increase in Antarctic sea ice in recent decades. So, how can more sea ice form on warmer ocean waters? As explained in an excellent article at skepticalscience.com, the reasons are complex. One reason is that the Southern Ocean consists of a layer of cold water near the surface and a layer of warmer water below. Water from the warmer layer rises up to the surface, melting sea ice. However, as air temperatures warm, the amount of rain and snowfall also increases. This freshens the surface waters, leading to a surface layer less dense than the saltier, warmer water below. The layers become more stratified and mix less. Less heat is transported upwards from the deeper, warmer layer. Hence less sea ice is melted (Zhang 2007). As the planet continues to warm, climate models predict that the growth in Antarctic sea ice will reverse, as the waters become too warm to support so much sea ice.


Figure 4. Surface air temperature over the ice-covered areas of the Southern Ocean surrounding Antarctica (top), and sea ice extent, observed by satellite (bottom). Image credit: (Zhang 2007).

Commentary: Earth's attic is on fire
To me, seeing the record Arctic sea ice loss of 2012 is like discovering a growing fire burning in Earth's attic. It is an emergency that requires immediate urgent attention. If you remove an area of sea ice 43% the size of the Contiguous U.S. from the ocean, it is guaranteed to have a significant impact on weather and climate. The extra heat and moisture added to the atmosphere as a result of all that open water over the pole may already be altering jet stream patterns in fall and winter, bringing an increase in extreme weather events. This year's record sea ice loss also contributed to an unprecedented melting event in Greenland. Continued sea ice loss will further increase melting from Greenland, contributing to sea level rise and storm surge damages. Global warming doubters tell us to pay attention to Earth's basement--the Antarctic--pointing out (incorrectly) that there is no fire burning there. But shouldn't we be paying attention to the steadily growing fire in our attic? The house all of humanity lives on is on fire. The fire is certain to spread, since we've ignored it for too long. It is capable of becoming a raging fire that will burn down our house, crippling civilization, unless we take swift and urgent action to combat it.

References
Funder, S. and K.H. Kjaer, 2007, "A sea-ice free Arctic Ocean?", Geophys. Res. Abstr. 9 (2007), p. 07815.

Kinnard et al., 2011, "Reconstructed changes in Arctic sea ice over the past 1,450 years".

Walsh, J.E and W.L.Chapman, 2001, "Twentieth-century sea ice variations from observational data", Annals of Glaciology, 33, Number 1, January 2001, pp. 444-448.

Related info
Half of the polar ice cap is missing: Arctic sea ice hits a new record low. September 6, 2012 blog post
Wunderground's Sea Ice page

Jeff Masters and Angela Fritz

Sea Ice Climate Change

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Nadine brushing the Azores; 94L could impact Canada on Sunday

By: JeffMasters, 12:25 PM GMT on September 20, 2012

Tropical Storm Nadine is headed east-southeast at 10 mph, parallel to the Azores Islands, and tropical storm warnings continue for portions of the island chain. Nadine brought sustained winds of 26 mph, gusting to 38 mph to Horta Castelo Branco in the Azores at 8:30 am local time, and occasional heavy rain showers have affected most of the islands today. Nadine is a very large storm, as seen on visible satellite loops, and will affect the islands for at least two more days as it treks slowly to the southeast of the islands. On Friday, Nadine is expected to convert to an extratropical storm due to cool waters and the influence of an upper-level low. The final fate of Nadine is very uncertain; the extratropical version of Nadine could continue moving eastward towards Portugal early next week, or move back to the west-southwest and potentially become a tropical storm again.


Figure 1. Morning satellite image of Tropical Storm Nadine brushing the Azores (at right of image) and of an extratropical storm (94L) with a 40% chance of becoming a subtropical storm by Saturday (center of image.)

Extratropical storm 94L east of Bermuda may acquire tropical characteristics
A large, cold-cored extratropical storm about 700 hundred miles east of Bermuda (Invest 94L) has a well-defined surface circulation, and has been over warm waters long enough to develop a respectable amount of heavy thunderstorm activity, as seen on visible satellite loops. This low has the potential to become a warm-cored subtropical storm this week. Wind shear is a moderate 10 - 20 knots, but the low has plenty of cold, dry air aloft that is slowing down transition to a subtropical storm. The low is over warm waters of 28°C, but the waters under 94L will cool to 26.5°C by Saturday, as the system tracks to the west-northwest at 10 mph. 94L should turn to the north by this weekend and potentially affect the Canadian Maritime Provinces on Sunday. In their 8 am EDT Tropical Weather Outlook, NHC gave the storm a 40% chance of becoming a subtropical or tropical cyclone by Saturday morning.

Elsewhere in the tropical Atlantic, none of the reliable computer models is predicting tropical cyclone development through September 26.

I'll have a new post late this morning on Arctic and Antarctic sea ice.

Jeff Masters

Updated: 1:47 PM GMT on September 20, 2012

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Tropical Storm Nadine brushing the Azores

By: JeffMasters, 2:57 PM GMT on September 19, 2012

Tropical Storm Nadine continues to churn towards the Azores Islands at 4 mph, where tropical storm warnings are up. Nadine brought sustained winds of 32 mph, gusting to 46 mph to Horta Castelo Branco in the Azores at 1:30 pm local time, and occasional heavy rain showers have affected most of the islands today. Nadine is a very large storm, as seen on visible satellite loops, and will affect the islands for at least three more days as it treks slowly to the southeast of the islands. On Thursday, Nadine will become tangled up with an upper-level low pressure system, and will convert to an extratropical storm. The final fate of Nadine is very uncertain; most of models predict that the two systems will merge, and the extratropical version of Nadine will move back to the west-southwest next week, where it could potentially become a tropical storm again. However, the GFS model predicts that Nadine and the upper-level low will remain separate, and extratropical storm Nadine will go on to hit Portugal and bring much-needed rain to the region on Monday. Much of Portugal and Spain are in moderate to severe drought, according to the Global Drought Monitor from the University College London.


Figure 1. Morning satellite image of Tropical Storm Nadine brushing the Azores (at right of image) and of an extratropical storm with a 10% chance of becoming a subtropical or extratropical cyclone by Friday (center of image.)

Extratropical storm east of Bermuda may acquire tropical characteristics
A large, cold-cored extratropical storm has formed about 800 hundred miles east of Bermuda, and has the potential to develop heavy thunderstorms that will enable it to become a warm-cored subtropical or tropical storm. Wind shear is a moderate to high 10 - 25 knots, and the low has plenty of cold, dry air aloft that will slow down any transition to a tropical storm. None of the reliable models develop this system into a tropical storm, though the latest runs of the GFS model and NOGAPS model predict that the system will begin to develop a warm core at low levels over the next few days. The storm is moving west at 10 mph, and should turn to the north by this weekend and potentially affect the Canadian Maritime Provinces. In their 8 am EDT Tropical Weather Outlook, NHC gave the storm a 10% chance of becoming a subtropical or tropical cyclone by Friday morning.

Elsewhere in the tropical Atlantic, none of the reliable computer models is predicting tropical cyclone development through September 25.

One interesting note on Typhoon Sanba, which hit Korea on Monday as a Category 1 storm with 90 mph winds. Sanba brought heavy rains to the coast of Russia, causing street flooding in Vladivostok. The city recorded 4.37" of rain (111 mm) over a 2-day period, causing a mudslide in the city that temporarily disrupted a train connection between two local stations. As pointed out to me by Maximiliano Herrera, significant typhoons impacts are uncommon in Russia, and Sanba was the 2nd typhoon to impact Vladivostok this year. On August 29, Typhoon Bolaven brought wind gusts of up to 73 mph to Vladivostok, and the rains from the storm helped put out wildfires burning in eastern Russia.

Jeff Masters

Hurricane

Updated: 3:42 PM GMT on September 19, 2012

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August 2012: Earth's 4th warmest August on record

By: JeffMasters, 3:07 PM GMT on September 18, 2012

August 2012 was the globe's 4th warmest August on record, according to the National Oceanic and Atmospheric Administration's National Climatic Data Center (NCDC). NASA rated August 2012 the 6th warmest on record. August 2012 global land temperatures were the 2nd warmest on record, and global ocean temperatures were the 5th warmest on record. August 2012 was the 330th consecutive month with global temperatures warmer than the 20th century average; the last time global temperatures were below average was February 1985. Global satellite-measured temperatures in August for the lowest 8 km of the atmosphere were 3rd warmest in the 34-year record, according to the University of Alabama Huntsville (UAH). Wunderground's weather historian, Christopher C. Burt, has a comprehensive post on the notable weather events of August in his August 2012 Global Weather Extremes Summary.



Figure 1. Departure of temperature from average for August 2012. Most areas of the world experienced much higher-than-average monthly temperatures, including much of Canada, Southeast Europe, and Western Asia. Central Russia was much cooler than average. Image credit: National Climatic Data Center (NCDC) .

El Niño watch continues
Sea surface temperatures were at 0.5°C above average as of September 17 in the equatorial Pacific off the coast of South America, and have been near or above the 0.5°C above average--the threshold needed for a weak El Niño event--since the beginning of July. However, winds, pressures, and cloud cover over the region have not responded in the fashion typically associated with an El Niño, and NOAA's Climate Prediction Center (CPC) classified conditions as being neutral in their September 6 El Niño discussion. They continued their El Niño watch, and gave a 69% chance that an El Niño event will be in place by the end of September. El Niño conditions tend to decrease Atlantic hurricane activity, by increasing wind shear over the tropical Atlantic. Wind shear has been close to average over the tropical Atlantic since the beginning of hurricane season in June. However, the past few runs of the GFS model have predicted a significant rise in wind shear over the Caribbean and tropical Atlantic by early October, which may represent El Niño finally beginning to kick in and affect the atmospheric circulation over the Atlantic.


Figure 2. Arctic sea ice extent as of September 18, 2012 (black line) compared to the previous record low years, in millions of square kilometers. This year's extent is far below any previous year, and is close to its minimum for the year. Satellite measurements of ice extent began in 1979. Image credit: Danish Meteorological Institute.

Arctic sea ice falls to all-time record low during August
August 2012 Arctic sea ice extent reached its lowest August extent in the 35-year satellite record, according to the National Snow and Ice Data Center (NSIDC). The new sea ice record was set on August 26, a full three weeks before the usual end of the melting season. Every major scientific institution that tracks Arctic sea ice agrees that new records for low ice area, extent, and volume have been set (see the comprehensive collection of sea ice graphs here.) Satellite records of sea ice extent date back to 1979, though a 2011 study by Kinnard et al. shows that the Arctic hasn't seen a melt like this for at least 1,450 years (see a more detailed article on this over at skepticalscience.com.) The latest September 18, 2012 extent of 3.5 million square kilometers is approximately a 50% reduction in the area of Arctic covered by sea ice, compared to the average from 1979 - 2000. The amount of open ocean exposed this September compared to September 1980 is about 43% of the size of the contiguous United States. The ice extent is close to its minimum for the year, and should start in increase within the next week or two, but that open water over the Arctic will provide a significant amount of heat and moisture to the atmosphere over the next few months that will significantly alter weather patterns. One possible impact may be an increase in the intensity and duration of extreme weather events during fall and winter.


Video 1. This animation shows the 2012 time-series of ice extent using sea ice concentration data from the DMSP SSMI/S satellite sensor. The black area represents the daily average (median) sea ice extent over the 1979-2000 time period. Layered over top of that are the daily satellite measurements from January 1 – September 14, 2012. A rapid melt begins in July, whereby the 2012 ice extents fall far below the historical average. Source: NOAA's Environmental Visualization Laboratory.

Nadine approaching the Azores
Long-lived Tropical Storm Nadine is headed northeastwards on a track that will bring the storm close to the Azores Islands on Wednesday and Thursday. A tropical storm watch has been posted for the islands of Flores and Corvo in the northwestern Azores. Steering currents for Nadine are expected to weaken on Wednesday, and the storm will move slowly and erratically for many days in the Central Atlantic late this week and early next week. On Friday, Nadine will become tangled up with an upper-level low pressure system, and the storm may partially or fully convert to an extratropical storm. By this weekend, the GFS and ECMWF models predict Nadine will move southwestward over warmer waters, and it could become fully tropical again.

Elsewhere in the Atlantic, thunderstorm activity associated with a tropical wave that moved through the Lesser Antilles Islands yesterday (92L) has diminished, and this wave is no longer a threat to develop. None of the reliable computers models is showing development of a new tropical cyclone in the Atlantic through September 24.

Jeff Masters

Climate Summaries

Updated: 6:09 PM GMT on September 18, 2012

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Category 1 Typhoon Sanba hits Korea; 92L and 93L not a threat

By: JeffMasters, 2:43 PM GMT on September 17, 2012

Typhoon Sanba battered South Korea on Sunday as a Category 1 typhoon with 90 mph winds. Sanba brought sustained winds of 46 mph, gusting to 69 mph, to Busan, South Korea, and heavy rains of 8.82" (212 mm) fell in 12 hours at Jeju, an island just south of the South Korean coast. Sanba is being blamed for two deaths and widespread power outages in South Korea and Southern Japan. Sanba has weakened to a tropical storm, and is lashing the North Korea and neighboring regions of China and Russia with heavy rains today. There are concerns that Sanba's rains will aggravate the food situation in North Korea, where two-thirds of the country's 24 million people are dealing with chronic food shortages. In August, Typhoon Bolaven flooded 127,500 acres of farmland in North Korea, and killed 59 in the country. Sanba pounded Okinawa, Japan early Sunday morning local time as a Category 3 storm with 120 mph winds, flooding 370 homes, mostly on the northern end of the island. Oku, on the northern tip of the island, experienced a gust of 124 mph (55.3 m/s), and 7 inches of rain fell on the island. Sanba became a Category 5 Super Typhoon with 175 mph winds for an 18-hour period ending at 12 UTC Friday, September 14, making it Earth's only Category 5 tropical cyclone so far in 2012.


Figure 1. Huge waves pound Yeosu City, South Korea, on September 17, 2012, as Category 1 Typhoon Sanba makes landfall. AP photo.


Figure 2. Radar image of Typhoon Sanba at landfall in South Korea at 9:50 am local time Monday September 17, 2012. Image credit: Korean Meteorological Agency.

Invest 92L in the Lesser Antilles
A tropical wave (Invest 92L) bringing a few heavy rain showers to the Lesser Antilles Islands is moving west at 15 mph. The wave is under a moderate 10 knots of wind shear, and has only a small amount of heavy thunderstorm activity, due to a large area of dry air surrounding the system. The amount of heavy thunderstorm activity has increased some this morning, though. The latest SHIPS model forecast predicts shear will be light to moderate, 5 - 20 knots, through Wednesday, which will favor development. However, the atmosphere over the Caribbean is unusually dry and stable, and this will make it difficult for 92L to organize quickly. 92L will bring heavy rain showers to the Dominican Republic on Wednesday, Jamaica, Haiti, and eastern Cuba on Thursday, the Cayman Islands and Central Cuba on Friday, and Mexico's Yucatan Peninsula, Honduras, and Western Cuba on Saturday. None of the reliable models develop the system. In their 8 am EDT Tropical Weather Outlook, NHC gave the wave a 0% of developing into a tropical depression by Wednesday morning, but these odds will probably rise as 92L reaches the Central Caribbean on Wednesday.


Figure 3. Morning satellite image of Invest 92L.

Invest 93L in the Gulf of Mexico no threat
An area of low pressure in the Northern Gulf of Mexico off the Louisiana coast (Invest 93L) is bringing heavy rains to the coast, but is moving inland, and development into a tropical depression will not occur.

Nadine may be around another week
Long-lived Tropical Storm Nadine has already been around a week, and may stick around at least another week, as it heads east-northeastward on a track that will bring the storm close to the Azores Islands on Wednesday and Thursday. Steering currents for Nadine are expected to collapse by Wednesday, and the storm will move slowly and erratically for many days in the Central Atlantic late this week and early next week. On Friday, Nadine will become tangled up with an upper-level low pressure system, and the storm may partially or fully convert to an extratropical storm. By this weekend, Nadine is expected to drift southwestward, and could become fully tropical again.


Figure 4. Hurricane Nadine as seen by the MODIS instrument on NASA's Terra satellite at 9:45 am EDT Sunday September 16, 2012. At the time, Nadine was at peak strength--a Category 1 hurricane with 80 mph winds. Image credit: NASA.

Jeff Masters

Hurricane

Updated: 6:49 PM GMT on October 03, 2012

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Category 2 Sanba closes in on Korea; 92L enters the Lesser Antilles

By: JeffMasters, 2:40 PM GMT on September 16, 2012

The winds are rising in Busan, South Korea, and heavy rain is lashing the Korean Peninsula and Southern Japan as Category 2 Typhoon Sanba steams northwards at 22 mph. Sanba pounded Okinawa, Japan early Sunday morning local time as a Category 3 storm with 120 mph winds, but no casualties or heavy damage has been reported thus far. Radar loops show that the large 35-mile diameter eye of Sanba passed over the northern part of Okinawa. Oku, on the northern tip of the island, experienced the eyewall, and recorded a gust of 124 mph (55.3 m/s). At Kadena Air Force Base, the eye of Sanba missed, passing just to the north. The winds peaked at 56 mph, gusting to 77 mph, at 8:30 am local time, after the eye passed to the northeast, and the base received 6.30" of rain. High wind shear of 25 - 35 knots is now affecting Sanba, and satellite loops show that the typhoon is weakening, with the cloud tops warming and dry air wrapping into the core. Radar out of Korea shows that heavy rains from Sanba cover most of the Korean Peninsula, and heavy rain is likely to be the main threat from Sanba in Korea. Sanba will continue to weaken as it encounters cooler waters and higher wind shear today, and is likely to be at Category 1 strength at landfall in South Korea near 22 UTC on Sunday.


Figure 1. Radar image of Typhoon Sanba over Okinawa at 6:25 am local time Sunday September 16, 2012. Image credit: Japan Meteorological Agency.


Video 1. Raw video of Typhoon Sanba hitting Okinawa, taken by storm chaser James Reynolds.

Sanba: the strongest tropical cyclone of 2012
Sanba became a Category 5 Super Typhoon with 175 mph winds for an 18-hour period ending at 12 UTC Friday, September 14, making it Earth's only Category 5 tropical cyclone so far in 2012 (there were two Category 5 storms in 2011, both in the Western Pacific.) The previous strongest tropical cyclone of 2012 was Super Typhoon Guchol, a Category 4 storm with top winds of 150 mph east of the Philippines in June. Sanba is the strongest typhoon in the Western Pacific since October 2010, when Super Typhoon Megi's sustained winds hit 180 mph.


Figure 2. Super Typhoon Sanba at peak strength, as seen at 04:50 UTC September 13, 2012, by the MODIS instrument on NASA's Aqua satellite. At the time, Sanba was a Super Typhoon with sustained winds of 175 mph and gusts to 205 mph. The spectacular eye of Super Typhoon Sanba featured two counter-rotating eddies at the surface. Image credit: NASA. NOAA's Environmental Visualization Laboratory has a spectacular large-scale image of Sanba at Category 5 strength.

Invest 92L entering the Lesser Antilles
A tropical wave (Invest 92L) entering the Lesser Antilles Islands is moving west at 15 mph, and is bringing heavy rain showers and gusty winds to the islands today. The wave is under a moderate 10 - 20 knots of wind shear, and has only a small amount of heavy thunderstorm activity, due to a large area of dry air surrounding the system. The amount of heavy thunderstorm activity has decreased since Saturday. The latest SHIPS model forecast predicts shear will fall to the 10 - 15 knot range Monday through Wednesday, which will favor development. However, the atmosphere over the Caribbean is unusually dry and stable, and this will make it difficult for 92L to organize quickly. 92L will bring heavy rain showers to the Dominican Republic and Haiti on Wednesday, Jamaica and eastern Cuba on Thursday, the Cayman Islands and Central Cuba on Friday, and Mexico's Yucatan Peninsula and Western Cuba on Saturday. The 06Z run of the NOGAPS models indicates some weak development of 92L once it reaches the Western Caribbean, but none of the other reliable models develop the system. In their 8 am EDT Tropical Weather Outlook, NHC gave the wave a 20% of developing into a tropical depression by Tuesday morning. A hurricane hunter aircraft is on call for Monday afternoon to investigate the storm, if necessary.


Figure 3. Morning satellite image of Invest 92L.


Hurricane Nadine headed towards the Azores Islands
Hurricane Nadine is heading eastward on a track that may bring the storm close to the Azores Islands on Wednesday. However, steering currents for Nadine are expected to collapse by Wednesday, and the storm will likely wander for many days in the Central Atlantic.

Jeff Masters

Hurricane

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Category 3 Typhoon Sanba hitting Okinawa

By: JeffMasters, 5:00 PM GMT on September 15, 2012

The winds are rising and heavy rain is lashing Okinawa, Japan where Category 3 Typhoon Sanba is expected to make landfall early Sunday morning local time (early this afternoon U.S. EDT.) Radar loops show that the large 35-mile diameter eye of Sanba is on a track that will bring it across the southern part of Okinawa, and heavy rains and wind gusts of 59 mph and 66 mph have been reported at Naha Airport and Kadena Air Force Base, respectively, over the past few hours. Moderate wind shear of 10 - 20 knots has weakened Sanba below its Category 5 peak on Friday morning, and satellite loops show that Sanba is weakening, with the cloud tops warming and the eyewall getting eroded on the west side, but Sanba should be able to maintain Category 3 strength as it crosses Okinawa today. Sanba will continue to weaken as it encounters cooler waters and higher wind shear between Okinawa and South Korea Saturday night and Sunday, and is likely to be at Category 1 strength at landfall in South Korea near 18 UTC on Sunday.


Figure 1. Radar image of Typhoon Sanba approaching Okinawa. Image credit: Japan Meteorological Agency.

Sanba: the strongest tropical cyclone of 2012
The most powerful tropical cyclone of 2012 is Typhoon Sanba. Sanba formed as a tropical depression over the western Pacific Ocean on September 10. The storm rapidly strengthened from a Category 1 to a Category 5 storm over very warm waters of 30°C (86°F) in just 24 hours beginning on September 13, and became Category 5 Super Typhoon with 175 mph winds for an 18-hour period ending at 12 UTC Friday, September 14. Sanba is Earth's only Category 5 tropical cyclone so far in 2012; the planet had two such storms in 2011, both in the Western Pacific. The previous strongest tropical cyclone of 2012 was Super Typhoon Guchol, a Category 4 storm with top winds of 150 mph east of the Philippines in June. Sanba is the strongest typhoon in the Western Pacific since October 2010, when Super Typhoon Megi's sustained winds hit 180 mph.



FIgure 2. Super Typhoon Sanba at peak strength, as seen at 04:50 UTC September 13, 2012, by the MODIS instrument on NASA's Aqua satellite. At the time, Sanba was a Super Typhoon with sustained winds of 175 mph and gusts to 205 mph. The spectacular eye of Super Typhoon Sanba featured two counter-rotating eddies at the surface. Image credit: NASA.

Links for Sanba
Radar loop from Okinawa
Live traffic with audio and video of Typhoon Sanba approaching.is available from ustream.tv.
Current conditions from Naha Airport, Okinawa, Japan
Current conditions from Kadena Air Force Base, Okinawa, Japan

Atlantic tropical update
Hurricane Nadine is recurving to the northeast on a track that may bring the storm close to the Azores Islands in 4 - 5 days. Steering currents for Nadine are expected to collapse in about 5 days, and the storm will likely wander for many days in the Central Atlantic.

A tropical wave about 600 miles east of the Lesser Antilles Islands is moving west at 15 mph, and will spread heavy rain showers and gusty winds over the islands on Sunday. The wave is under a moderate 10 - 20 knots of wind shear, and has only a small amount of heavy thunderstorm activity, due to a large area of dry air surrounding the system. The amount of heavy thunderstorm activity has increased some this afternoon, though. The 12Z run of the NOGAPS model predicts the wave could approach tropical depression strength by Wednesday, when it will be near the Dominican Republic. However, none of the other reliable models develop the system, and the wave doesn't have much spin at present, as seen on an 11:14 am EDT ASCAT pass.. In their 2 pm EDT Tropical Weather Outlook, NHC gave the wave a 20% of developing into a tropical depression by Monday afternoon. A hurricane hunter aircraft is on call for Monday afternoon to investigate the storm, just in case.

Jeff Masters

Hurricane

Updated: 5:38 PM GMT on September 15, 2012

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The new hottest place on Earth: Death Valley, California

By: JeffMasters, 1:18 PM GMT on September 13, 2012

As any weather aficionado can avow, Earth's most iconic weather record has long been the legendary all-time hottest temperature of 58°C (136.4°F) measured 90 years ago today at El Azizia, Libya on September 13, 1922. One hundred thirty six degrees! It's difficult to comprehend that heat like that could exist on our planet. For 90 years, no place on Earth has come close to beating the unbelievable 136 degree reading from Al Azizia, and for good reason--the record is simply not believable. But Earth's mightiest weather record has been officially cast down. Today, the official arbiter of Earth's weather records, the World Meteorological Organization (WMO), announced that the all-time heat record held for exactly 90 years by El Azizia in Libya "is invalid because of an error in recording the temperature." The WMO committee found five major problems with the measurement. Most seriously, the temperature was measured in a paved courtyard over a black, asphalt-like material by a new and inexperienced observer, not trained in the use of an unsuitable replacement instrument that could be easily misread. The observer improperly recorded the observation, which was consequently in error by about 7°C (12.6°F.) The new official highest hottest place on the planet is now Death Valley, California. A remarkable high temperature of 56.7°C (134°F) was measured there on 10 July 1913, at Greenland Ranch.


Figure 1. The trading post at Al Azizia, Libya in 1923. The photo was taken from the Italian military fort located on a small hill just south of the trading post. It was at this fort that the temperature of 58°C (136.4°F) was observed on Sept. 13, 1922 (used with permission from the family of Gen. Enrico Pezzi).

The story behind the overturning of Earth's most hallowed weather record
Today's announcement is the culmination of a 3-year research effort begun by wunderground weather historian, Christopher C. Burt. His blog post today, World Heat Record Overturned--A Personal Account, provides a fascinating detective story on how the record came to be cast down--and how the Libyan revolution of 2012 almost prevented this from happening.


Figure 2. The new official hottest place on the planet: Death Valley, California. Wide open spaces, infinite views, intensely salty water, mind-boggling heat. What's not to love about this place? Image credit: Wunderphotographer SonomaCountyRAF.

Dead Heat: The Video
Don't miss the 25-minute wunderground video, Dead Heat, a detective story on how the El Azizia record was overturned.

Atlantic tropical update
Tropical Storm Nadine is recurving to the northwest and north well east of the Lesser Antilles Islands, on a track that would likely keep this storm far out at sea away from any land areas. However, Nadine may eventually threaten the Azores Islands or Newfoundland; the models are divided on how the steering currents will evolve next week, and we cannot be sure which way Nadine will go during the middle of next week.

The models predict that a trough of low pressure off the U.S. East Coast may serve as the focus for development of a non-tropical low pressure system on Sunday or Monday, but this low will likely form too far to the north to become a tropical storm. The GFS model has been predicting a tropical wave coming off the coast of Africa may develop next week, but has not been consistent with the timing or location of the development.

In the Western Pacific, Super Typhoon Sanba is an impressive top-end Category 4 storm with 155 mph winds, and is headed north-northwest towards a possible landfall in Korea early next week.

Given the importance of the new world record all-time high temperature, I'll leave this post up until Saturday afternoon, when I'll post an update on the tropics.

Jeff Masters

Heat Extreme Weather

Updated: 1:53 PM GMT on September 13, 2012

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Tropical Storm Nadine forms; Newfoundland cleans up after Leslie

By: JeffMasters, 3:03 PM GMT on September 12, 2012

Tropical Storm Nadine formed last night, midway between Africa and the Lesser Antilles Islands, and continues to grow more organized today as it heads west-northwest at 17 mph. The models unanimously predict that Nadine will recurve to the north well east of the Lesser Antilles Islands later this week, on a track that would likely keep this storm far out at sea away from any land areas. Nadine is in a low-shear environment favorable for strengthening, and will likely become Hurricane Nadine by Thursday. A NASA remotely-piloted Global Hawk research aircraft is currently flying a 26-hour mission in Nadine, as part of the HS3 Hurricane and Severe Storm Sentinel Program. The data collected will help scientists decipher the relative roles of the large-scale environment and internal storm processes that affect hurricanes.

With fourteen named storms already this season, 2012 is now one of just 19 hurricane seasons over the past 162 years to have fourteen or more tropical storms. Nadine's formation date of September 10 puts 2012 in 5th place for earliest formation date of the season's 14th tropical storm. Only 2005, 2011, 1936, and 1933 had earlier formation dates of the season's 14th storm.


Figure 1. Morning satellite image of Tropical Storm Nadine.

Elsewhere in the Atlantic
Most of the models predict that a trough of low pressure about 600 miles off the U.S. East Coast will serve as the focus for development of a non-tropical low pressure system on Sunday or Monday. This low may spend enough time over water to acquire tropical characteristics and become a named storm by the middle of next week.

Newfoundland cleans up after Tropical Storm Leslie
Tropical Storm Leslie made landfall in Southern Newfoundland at 8 am EDT September 11 as a tropical storm with 70 mph winds and a central pressure of 969 mb. Leslie brought sustained winds to Newfoundland's capital, St. Johns, of 58 mph, gusting to 82 mph, at 10:30 am local time. Cape Pine record the highest gust from Leslie, 85 mph. The storm tore off roofs, downed trees, and toppled power lines, and 45,000 households were without power Tuesday afternoon in Newfoundland, including much of the capital of St. Johns. Leslie's tropical moisture collided with the cold front drawing the storm to the north, resulting in heavy rains over eastern Nova Scotia and western Newfoundland in excess of 4 inches, which caused considerable flooding of homes and streets. However, the rains were far less than those experienced during Hurricane Igor, which hit Newfoundland as a Category 1 hurricane in 2010, causing $200 million in damage. I expect damage from Leslie will be less than $20 million. Leslie is now a powerful extratropical storm bringing rain and strong winds to Iceland.

Jeff Masters

Hurricane

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Tropical Storm Leslie hits Newfoundland; TD 14 forms

By: JeffMasters, 2:55 PM GMT on September 11, 2012

Tropical Storm Leslie zoomed ashore over Newfoundland this morning near 8 am EDT, traveling with a forward speed of 40 mph. Leslie brought sustained winds to the capital of St. Johns of 58 mph, gusting to 82 mph, at 10:30 am local time. At least three other stations in Newfoundland recorded gusts over hurricane force: Cape Pine (85 mph), Bonavista (77 mph), and Argentia (74 mph). Damage to buildings has been reported in St. Johns, and the storm has knocked out power to much of Southeast Newfoundland, including the capital. Leslie's tropical moisture collided with the cold front drawing the storm to the north, resulting in heavy rains over Nova Scotia in excess of 4 inches, which caused considerable flooding of homes and streets. Overall, though, the damage to Canada appears to be far less than that of Hurricane Igor, which hit Newfoundland as a Category 1 hurricane in 2010, causing $200 million in damage. Leslie has now transitioned to a powerful extratropical storm, and will bring heavy rains to Iceland on Thursday, and to Scotland on Friday.


Figure 1. Tropical Storm Leslie as it crossed Newfoundland at 9:46 am EDT September 11, 2012. At the time, Leslie had top winds of 70 mph. The cloud pattern of Leslie looks more extratropical than tropical, and Leslie was no longer a tropical storm at this time. Tropical Storm Michael is visible at lower right, as a tight swirl of low clouds.

Hurricane Michael dying
The longest-lived hurricane of the 2012 Atlantic hurricane season was Michael, which attained hurricane status at 11 pm EDT September 5 and finally weakened to a tropical storm at 5 am EDT this morning. Satellite loops show that Michael has lost almost all of its heavy thunderstorms, and is racing to the northeast over colder waters. Michael will likely be declared dead later today.

Tropical Depression 14 forms
Tropical Depression Fourteen has formed midway between Africa and the Lesser Antilles Islands, from a tropical wave that emerged off the coast of Africa on Friday. The models unanimously predict that TD 14 recurve to the north well east of the Lesser Antilles Islands later this week, on a track that would likely keep this storm far out at sea away from any land areas. TD 14 is in a low-shear environment favorable for strengthening, and will likely become Tropical Storm Nadine by Wednesday.

Elsewhere in the Atlantic
The ECMWF model predicts that the cold front that swept off the U.S. East Coast Monday will leave a trough of low pressure over the ocean which could serve as the focus for development of a tropical or subtropical depression several hundred miles off the coast of North Carolina late this week.


Figure 2. Visible NOAA GOES-7 satellite image of Hurricane Iniki just before landfall in Hawaii at 8:01 pm EDT September 11, 1992. Iniki completed a “clean sweep” of National Weather Service offices responsible for issuing hurricane warnings. The National Hurricane Center in Coral Gables, Florida (Hurricane Andrew), the Joint Typhoon Warning Center in Guam (Typhoon Omar), and the Central Pacific Hurricane Center in Honolulu, Hawaii (Hurricane Iniki) were all struck by strong hurricanes within a 2-month span in 1992. Image credit: NOAA Environmental Visualization Lab.

20th anniversary of Hurricane Iniki
Twenty years ago today, Hurricane Iniki, the most powerful hurricane on record to strike the state of Hawaii, made landfall on the island of Kauai as a Category 4 storm with sustained winds of 145 mph and gusts up to 175 mph. Iniki brought storm tides of 4.5 - 6 feet (1.4 - 1.8 m) to Kauai, with high water marks of up to 18 feet (5.5 m) being measured due to large waves on top of the surge. Waves up to 35 feet (10.5 m) battered the southern coastline for several hours, causing a debris line of more than 800 feet (250 m) inland. The hurricane's high winds did incredible damage to structures on the island--5,152 homes were severely damaged, and some parts of the island were without power for three months. Iniki's $3 billion damage (2012 dollars) made the hurricane the second costliest Eastern Pacific hurricane, trailing Hurricane Paul, which made landfall in Mexico in 1982. Iniki holds the Eastern Pacific record for lowest pressure for a landfalling hurricane--945 mb (27.91").

Jeff Masters

Hurricane

Updated: 3:07 PM GMT on September 11, 2012

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Summer 2012: 3rd hottest in U.S. history

By: JeffMasters, 4:48 PM GMT on September 10, 2012

The summer of 2012 was the 3rd hottest summer in U.S. history, said NOAA's National Climatic Data Center (NCDC) in today's State of the Climate report. June 2012 ranked as the 14th warmest June on record, August was the 16th warmest August on record, and July was the warmest month of any month in U.S. history, bringing the average summer temperature of the contiguous U.S. just 0.2°F shy of the hottest summer on record--the great Dust Bowl summer of 1936. Second place is held by 2011, which was just 0.1°F cooler than the summer of 1936. So far in 2012, we've had the warmest March on record, 3rd warmest April, 2nd warmest May, and warmest July. These remarkably warm months have helped push temperatures in the contiguous U.S. to the warmest on record for the year-to-date period of January - August. Temperatures this year in the U.S. have been so far above the previous record--a remarkable 1°F for the year-to-date period--that even if the remainder of 2012 ranks historically in the coldest one-third of September - Decembers on record, 2012 will beat out 1998 for the warmest year in history. Reliable weather records for the U.S. go back to 1895. The most recent 12-month period of September 2011 - August 2012 was the 4th warmest 12-month period in U.S. history, exceeded only by the 12-month periods ending in July, June, and May of this year.


Figure 1. The summer of 2012 was the warmest on record for Wyoming and Colorado, and ranked in the top-ten warmest on record for 22 other states. For the Contiguous U.S., it was the 3rd warmest summer since record keeping began in 1895. Image credit: NOAA's National Climatic Data Center (NCDC).


Figure 2. Year-to-date temperatures for the contiguous U.S. through August, compared to the previous record warmest years in U.S. history. Outcome scenarios based on persistence of temperature from September through December, the remaining five months of 2012, are shown. Even if the remainder of 2012 ranks historically in the coldest one-third of September - Decembers on record, 2012 will beat out 1998 for the warmest year in history. The January-August 2012 contiguous U.S. average temperature was 58.7°F, 4.0°F above average. The data for 2012 are preliminary. Image credit: NOAA/NCDC.

Most extreme January - August period on record
The year-to-date period was the most extreme in U.S. history, according to NOAA's U.S. Climate Extremes Index (CEI), which tracks the percentage area of the contiguous U.S. experiencing top-10% and bottom-10% extremes in temperature, precipitation, and drought. The CEI was 47% during the year-to-date January - August period. This is the highest value since CEI record-keeping began in 1910, and more than double the average value of 20%. Remarkably, 85% of the contiguous U.S. had maximum temperatures that were in the warmest 10% historically during the first eight months of 2012, and 75% of the U.S. of the U.S. had warm minimum temperatures in the top 10%. The percentage area of the U.S. experiencing top-10% drought conditions was 22%, which was the 11th greatest since 1910.


Figure 3. NOAA's U.S. Climate Extremes Index (CEI) for January - August shows that 2012 had the most extreme first eight months of the year on record, with 47% of the contiguous U.S. experiencing top-10% extreme weather.

Jeff Masters

Climate Summaries

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Leslie bears down on Newfoundland; TD 14 forming

By: JeffMasters, 2:27 PM GMT on September 10, 2012

Tropical Storm Leslie has left Bermuda behind, and is chugging north-northeastwards at 18 mph towards an early Tuesday morning encounter with Newfoundland. Leslie brushed by Bermuda on Sunday, with the core of the storm passing 120 miles to the east of the island. The highest winds in Bermuda occurred at Saint David's weather station on the east end of the island, where Leslie brought sustained winds of 39 mph, gusting to 54 mph, at 12:31 pm AST. The station picked up 3.15" of rain from Leslie. A few scattered power outages occurred on Bermuda, but no major damage was reported.


Figure 1. Predicted rainfall from Tropical Storm Leslie, as forecasted by the 2 am EDT September 10, 2012 run of the GFDL model. A large area of 4 - 8 inches of rain (dark green colors) is predicted for western Newfoundland and eastern Nova Scotia. Image credit: Morris Bender, NOAA/GFDL.

Forecast for Leslie
Satellite loops show that Leslie has failed to form an eyewall, and the entire southwest quadrant of the storm is devoid of any heavy thunderstorms. The storm's large size and limited time over warm water will keep it from becoming any stronger than a Category 1 hurricane with 75 mph winds at landfall in Newfoundland near 4 am EDT on Tuesday morning, and it is more likely that Leslie will have top winds just below hurricane strength, 65 - 70 mph. The latest 5 am EDT NHC wind probability forecast calls for a 31% chance that Leslie will be a Category 1 or stronger hurricane Tuesday morning at 2 am EDT, when the storm will be near the coast of Newfoundland. Leslie's strongest winds will be felt on the Avalon Peninsula, on the southeast portion of the island, and the capital of St. Johns will likely experience sustained winds of 45 - 60 mph on Tuesday during the peak of the storm. However, heavy rain will be the main threat from Leslie, and the heaviest rains will fall to the west of the center, where Leslie will be interacting with a cold front. The latest 2 am EDT runs of the GFDL and HWRF models suggest that western Newfoundland and eastern Nova Scotia may receive 4 - 8 inches of rain, which would likely cause moderate to major floods on area rivers.


Figure 2. Tropical Storm Leslie and Hurricane Michael at seen at 9:15 am EDT Monday September 10, 2012. At the time, Leslie had top winds of 60 mph, and Michael was a Category 1 hurricane with 80 mph winds.

Hurricane Michael remains a Category 1 hurricane
The longest-lived hurricane of the 2012 Atlantic hurricane season is Hurricane Michael, which attained hurricane status at 11 pm EDT September 5. Michael remains a Category 1 hurricane with 80 mph winds today, and satellite loops show that Michael is still an impressive storm with a well-developed eye. None of the models show that Michael will threaten any land areas, and Michael will likely weaken below hurricane strength tonight and die at sea over cold waters southeast of Newfoundland in 2 - 3 days.

91L about to become Tropical Depression 14
A tropical wave that emerged off the coast of Africa on Friday (Invest 91L) is about to become Tropical Depression Fourteen, midway between Africa and the Lesser Antilles Islands. Our two most reliable models, the GFS and ECMWF, predict that 91L will pass at least 500 miles to the northeast of the Lesser Antilles Islands late this week, on a track that would likely keep this storm far out at sea away from any land areas.

Elsewhere in the Atlantic
Several of our reliable models predict that the cold front currently sweeping off the U.S. East Coast will leave a trough of low pressure over the ocean near Bermuda late this week, which may serve as the focus for development of a new tropical depression. Any storm that develops in this region would likely have a complicated and difficult-to-predict interaction with 91L (soon to be TD 14), which will pass close to the east.

With today marking the climatological halfway point of the Atlantic hurricane season, the hurricane season of 2012 shows no signs of slowing down from its near-record pace of generating new named storms. Two more tropical waves are predicted to come off the coast of Africa later this week and early next week, and it would not be surprise to see one of these new waves develop by early next week. Today's El Niño discussion from NOAA/CPC shows a continuation of El Niño conditions in the Eastern Pacific, but the atmosphere stubbornly refuses to respond much to the heating of the waters. Wind shear remains seasonably low over the tropical Atlantic Ocean, and is predicted to remain so for at least the next ten days.

Jeff Masters

Hurricane

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Leslie brushing Bermuda, heading for Newfoundland

By: JeffMasters, 4:40 PM GMT on September 09, 2012

It's a wet, windy day on Bermuda today, where Tropical Storm Leslie is bringing high winds and heavy rain as the storm's core passes 120 miles (200 km) east of the island. At the Saint David's weather station on the east end of the island, Leslie brought sustained winds of 39 mph, gusting to 54 mph, at 12:30 pm AST today. Bermuda radar shows a large area of heavy rain from Leslie is over the island, and these rains will continue through most of the afternoon, and the Bermuda airport is closed until 4 pm AST. Satellite loops show that Leslie is a large storm with a huge eye 60 miles (100 km) in diameter, but the storm does not have an eyewall.


Figure 1. Radar image of Tropical Storm Leslie from the Bermuda radar, taken at 12:43 AST.

Forecast for Leslie
As Leslie continues to move north over warmer water, the storm should be able to build an eyewall and become a Category 1 hurricane. The strong trough of low pressure pulling Leslie to the north will bring Leslie very close to Newfoundland, Canada by Tuesday. At that time, Leslie should be weakening due to cooler waters and increased wind shear, and is likely to be a tropical storm. Heavy rain will be the main threat to Newfoundland. The latest 11 am EDT NHC wind probability forecast calls for a 36% chance that Leslie will be a Category 1 or stronger hurricane Tuesday morning at 8 am EDT, when the storm will be near Newfoundland. Even if the core of Leslie misses Newfoundland, the island will still likely experience tropical storm-force winds, since 39+ mph winds are expected to extend outward from its center 160 miles to its northwest on Tuesday. Large swells from Leslie continue to pound the entire Eastern Seaboard, and are creating beach erosion and dangerous rip currents.


Figure 2. Tropical Storm Leslie as seen by NOAA's F-16 polar orbiting satellite at 9:20 am EDT Sunday September 9, 2012. At the time, Leslie had top winds of 60 mph. Bermuda is the yellow triangle at the left of the image. Image credit: NOAA/RAMMB.

Hurricane Michael weakens to Category 1
Hurricane Michael has weakened to a Category 1 storm with 90 mph winds, out over the open mid-Atlantic Ocean. Satellite loops show that Michael is still an impressive storm with a well-developed eye. None of the models show that Michael will threaten any land areas during the coming five days, and Michael will likely die at sea over cold waters east of Newfoundland in 3 - 4 days.


Figure 3. Hurricane Michael as seen by NASA's Terra satellite at 9:40 am EDT Sunday September 9, 2012. At the time, Michael was a Category 1 hurricane with 90 mph winds. Image credit: NOAA/RAMMB.

91L off the coast of Africa
A tropical wave that emerged off the coast of Africa on Friday (Invest 91L) is 250 miles west of the Cape Verde Islands, and is headed west-northwest at 10 - 15 mph. The disturbance is large with plenty of spin, but has limited heavy thunderstorm activity due to dry air. Most of the reliable computer models are predicting that 91L will develop into a tropical depression by Wednesday. In their 8 am EDT Tropical Weather Outlook, NHC gave 91L a 40% chance of developing into a tropical depression by Tuesday morning. Our two most reliable models, the GFS and ECMWF, predict that 91L will pass at least 500 miles to the northeast of the Lesser Antilles Islands late this week, on a track that would likely keep this storm far out at sea away from any land areas.

Jeff Masters

Hurricane

Updated: 4:41 PM GMT on September 09, 2012

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Severe weather in the Northeast U.S.; updates on 90L, 91L, Leslie and Michael

By: JeffMasters, 4:07 PM GMT on September 08, 2012

A significant severe weather outbreak is underway today across much of the Northeastern U.S., including metro New York City and Philadelphia. NOAA's Storm Prediction Center has placed the region in their "Moderate Risk" area for severe weather. A fall-like low pressure system with a very powerful cold front will sweep through the region today, triggering widespread severe thunderstorms that may organize into a "derecho" event with damaging winds covering a large swath of the Northeast. A few tornadoes may accompany the event, and several tornado warnings have already been issued in New York, with a possible tornado touchdown in the Point Breeze section of the Rockaway peninsula in Queens. The same storm system killed four people on Friday in northeast Oklahoma; three of the deaths occurred when strong thunderstorms winds blew a mobile home into a ravine. Record heat was observed in advance of the storm's cold front yesterday; Wichita Falls, TX hit a record high of 109, the hottest temperature ever recorded there so late in the season. When the cold front blew through at 7 pm CDT, the temperature dropped 15 degrees in 16 minutes, falling to 66 degrees by midnight. Wunderground meteorologist Shaun Tanner has more on the severe weather potential for the Northeast in his blog.


Figure 1. Severe weather potential for Saturday, September 8, 2012.

90L in the Gulf not a threat to develop
A partial remnant of Hurricane Isaac off the coast of the Florida Panhandle, Invest 90L, continues to be disrupted by wind shear, and no longer has time to develop before landfall occurs along the Florida Gulf Coast tonight or Sunday. Visible satellite loops show that 90L has a small area of poorly organized heavy thunderstorms, which will bring some areas of heavy rain to Florida today and Sunday.

Leslie still struggling with cool waters
Tropical Storm Leslie continues to feel the impact of the the cool waters it stirred up due to its long pause south of Bermuda, and remains a 65 mph tropical storm. The storm has no eyewall, as seen on satellite loops, but has cleared out a large cloud-free center. As Leslie continues to move north over warmer water, the storm should be able to build an eyewall and become at least a Category 1 hurricane. However, Leslie is expected to pass far enough to the east of Bermuda today and tonight that top winds of 45 mph will be observed on the island. Bermuda radar shows a large area of heavy rain from Leslie is very close to the island.


Figure 2. Morning radar image of Tropical Storm Leslie from the Bermuda radar.

Forecast for Leslie
The strong trough of low pressure pulling Leslie to the north will bring Leslie very close to Newfoundland, Canada by Tuesday night or Wednesday morning. At that time, Leslie should be weakening due to cooler waters and increased wind shear, and is likely to be a tropical storm. Heavy rain will be the main threat to Newfoundland. The latest 11 am EDT NHC wind probability forecast calls for a 24% chance that Leslie will be a Category 1 or stronger hurricane Wednesday morning at 8 am EDT, when the storm will be near Newfoundland. Even if the core of Leslie misses Newfoundland, the island will still likely experience tropical storm-force winds, since 39+ mph winds will probably extend outward from its center 180 miles to its west on Tuesday and Wednesday. Large swells from Leslie continue to pounding the entire Eastern Seaboard, and are creating beach erosion and dangerous rip currents.


Figure 3. Hurricane Michael as seen by NASA's Aqua satellite at 11:50 am EDT Friday September 7, 2012. At the time, Michael was a Category 2 hurricane with 105 mph winds. Image credit: NASA.

Hurricane Michael weakens to Category 2
Hurricane Michael remains a Category 2 storm with 105 mph winds, out over the open mid-Atlantic Ocean. Satellite loops show that Michael is still an impressive storm with a well-developed eye. None of the models show that Michael will threaten any land areas during the coming five days, and Michael will likely die at sea over cold waters northeast of Newfoundland in 5 - 7 days.

91L off the coast of Africa
A tropical wave that emerged off the coast of Africa on Friday has been designated Invest 91L by NHC today. Most of the reliable computer models are predicting that 91L will develop into a tropical depression by Wednesday. None of the reliable computer models foresee that this storm will be a threat to the Lesser Antilles Islands, but it is still early to be assuming that 91L will recurve harmlessly out to sea.

Jeff Masters

Hurricane Severe Weather

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90L in the Gulf disorganized; Leslie and Michael weaken

By: JeffMasters, 4:27 PM GMT on September 07, 2012

A partial remnant of Hurricane Isaac off the coast of Louisiana, Invest 90L, was almost torn apart last night by wind shear, but is making a bit of a comeback today. Visible satellite loops and surface observations from buoys and oil rigs in the Gulf show that 90L has an sloppy, elongated surface circulation. The area covered by heavy thunderstorms is relatively modest, and has been pushed to the south side of the circulation center by strong northerly winds that are creating a high 20 knots of wind shear. There is a large amount of dry air that surrounds 90L on all sides that is interfering with development. A hurricane hunter aircraft scheduled to investigate 90L today was cancelled, and has been rescheduled for Saturday afternoon.


Figure 1. Visible satellite image of Invest 90L taken at 11:58 am EDT Friday September 7, 2012.

Forecast for 90L
Wind shear over 90L is predicted to stay in the moderate to high range, 15 - 20 knots, through Saturday morning, then drop to the low range Saturday afternoon through Sunday. Ocean temperatures in the Gulf are 28.5° - 29°C, which is plenty warm enough to support formation of a tropical storm. 90L is essentially stationary this morning, but should begin a slow motion to the east-northeast tonight, in response to the steering flow from a trough of low pressure and its associated surface cold front approaching the Gulf Coast from the northwest. This trough should be capable of pulling 90L to a landfall along the Florida Panhandle or west coast of Florida by Sunday morning. In their 8 am Tropical Weather Outlook, NHC gave 90L a 20% chance of developing into a tropical depression by Sunday morning. I put these odds higher, at 30%.

Leslie weakens to a tropical storm
Tropical Storm Leslie continues to remain nearly stationary to the south of the island of Bermuda, and a NOAA hurricane hunter aircraft found this morning that Leslie had weakened below hurricane strength, to a 70 mph tropical storm. An ocean probe launched by the aircraft found that the ocean temperatures at one location in Leslie were 24.5°C, a full 5°C (8°F) drop from when the storm first reached the area two days ago. Moderate wind shear of 10 - 20 knots due to strong upper-level winds out of the west continue to drive dry air to Leslie's west into the core of the storm. The combined effect of shear and cool waters have eroded away Leslie's core, and the storm has no eyewall, as seen on satellite loops. A NOAA hurricane hunter aircraft will be in the storm tonight, and an uncrewed NASA Global Hawk aircraft finished an HS3 Hurricane Research Mission into Leslie this morning.


Figure 2. Hurricane Leslie as seen by NASA's Aqua satellite at 10:45 am EDT Thursday, September 6, 2012. At the time, Leslie was a Category 1 hurricane with 75 mph winds. Image credit: NASA.

Forecast for Leslie
A strong trough of low pressure approaching the U.S. East Coast should make Leslie start moving to the north at 5 mph by Saturday morning. The models have stayed with their more eastwards solution to Leslie's track, which keeps the threat of Bermuda receiving hurricane-force winds relatively low, since the island is expected to be on the weak (left) side of the storm. If the official NHC forecast verifies, tropical storm-force winds will just graze Bermuda Sunday morning through Sunday evening. According to the latest SHIPS model forecast, the shear is expected to fall to the low category, 5 - 10 knots, by Friday night. Leslie is over warm ocean waters of 29 - 30°C, and once the storm moves away from the large pool of cool waters it has stirred up, the reduction in shear and warm waters should allow the storm to intensify to at least a Category 1 hurricane by Sunday. The latest 11 am EDT NHC wind probability forecast calls for a 30% chance that Leslie will be a Category 2 or stronger hurricane Sunday morning at 8 am EDT, when the storm will be beginning its closest pass to Bermuda. Leslie is a huge storm, and tropical storm-force winds are expected to extend outward from its center 200 - 220 miles by Sunday.

Most of the models indicate Leslie is likely to make landfall in Newfoundland, Canada on Tuesday night or Wednesday morning. However, the models have been trending more to the east with Leslie's track in recent runs, and given the uncertainty in 4-day hurricane forecasts, the storm could very well miss the island, passing to the northeast. Large swells from Leslie are pounding the entire Eastern Seaboard, and are creating beach erosion and dangerous rip currents.


Figure 3. Hurricane Michael as seen by NASA's Aqua satellite at 12:20 pm EDT Thursday September 6, 2012. At the time, Michael was a Category 3 hurricane with 115 mph winds. Image credit: NASA.

Hurricane Michael weakens to Category 2
The only major hurricane of the 2012 Atlantic hurricane season, Hurricane Michael, has weakened, and is now a Category 2 storm with 105 mph winds. Satellite loops show that Michael is still an impressive storm with a well-developed eye, but the storm is not as symmetric, and the eye no longer as distinct as was the case yesterday. Michael is far out over the open Atlantic, and none of the models show that Michael will threaten any land areas during the coming seven days.

Elsewhere in the Atlantic
Most of the reliable computer models are predicting that a new tropical wave moving off the coast of Africa today will develop into a tropical depression by the middle of next week. This wave is predicted to exit Africa too far north to threaten the Lesser Antilles Islands.

Jeff Masters

Hurricane

Updated: 4:29 PM GMT on September 07, 2012

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Half of the polar ice cap is missing: Arctic sea ice hits a new record low

By: JeffMasters, 8:53 PM GMT on September 06, 2012

Extraordinary melting of sea ice in the Arctic this summer has shattered the all-time low sea ice extent record set in September 2007, and sea ice continues to decline far below what has ever been observed. The new sea ice record was set on August 26, a full three weeks before the usual end of the melting season, according to the National Snow and Ice Data Center. Every major scientific institution that tracks Arctic sea ice agrees that new records for low ice area, extent, and volume have been set. These organizations include the University of Washington Polar Science Center (a new record for low ice volume), the Nansen Environmental & Remote Sensing Center in Norway, and the University of Illinois Cryosphere Today. A comprehensive collection of sea ice graphs shows the full story. Satellite records of sea ice extent date back to 1979, though a 2011 study by Kinnard et al. shows that the Arctic hasn't seen a melt like this for at least 1,450 years (see a more detailed article on this over at skepticalscience.com.) The latest September 5, 2012 extent of 3.5 million square kilometers is approximately a 50% reduction in the area of Arctic covered by sea ice, compared to the average from 1979 - 2000. The ice continues to melt, and has not reached the low for this year yet.


Figure 1. A sunny, slushy day at the North Pole on September 1, 2012. Webcam image courtesy of the North Pole Environmental Observatory.


Figure 2. Sea ice extent on September 5, 2012, showed that half of the polar ice cap was missing, compared to the average from 1979 - 2000. Image credit: National Snow and Ice Data Center.

Why the Arctic sea ice is important
Arctic sea ice is an important component of the global climate system. The polar ice caps help to regulate global temperature by reflecting sunlight back into space. White snow and ice at the poles reflects sunlight, but dark ocean absorbs it. Replacing bright sea ice with dark ocean is a recipe for more and faster global warming. The Autumn air temperature over the Arctic has increased by 4 - 6°F in the past decade, and we could already be seeing the impacts of this warming in the mid-latitudes, by an increase in extreme weather events. Another non-trivial impact of the absence of sea ice is increased melting in Greenland. We already saw an unprecedented melting event in Greenland this year, and as warming continues, the likelihood of these events increase.


Figure 3. August set a new record for lowest Arctic sea ice extent. Image credit: National Snow and Ice Data Center.



Figure 4. Arctic sea ice death spiral as plotted by Jim Pettit using data from the Japan Aerospace Exploration Agency.

Huge storm pummels Alaska
A massive low pressure system with a central pressure of 970 mb swept through Alaska on Tuesday, generating hurricane-force wind gusts near Anchorage, Alaska that knocked out power to 55,000 homes. Mighty Alaskan storms like this are common in winter, but rare in summer and early fall. The National Weather Service in Anchorage said in their Wednesday forecast discussion that the forecast wind speeds from this storm were incredibly strong for this time of year--four to six standard anomalies above normal. A four-standard anomaly event occurs once every 43 years, and a five-standard anomaly event is a 1-in-4800 year event. However, a meteorologist I heard from who lives in the Anchorage area characterized the wind damage that actually occurred as a 1-in-10 year event. A few maximum wind gusts recorded on Tuesday during the storm:

McHugh Creek (Turnagain Arm)... ... ..88 mph
Paradise Valley (Potter Marsh)... ... 75 mph
Upper Hillside (1400 ft)... ... ... ... 70 mph
Anchorage port... ... ... ... ... ... ... .63 mph

The storm has weakened to a central pressure of 988 mb today, and is located just north of Alaska. The storm is predicted to bring strong winds of 25 - 35 mph and large waves to the edge of the record-thin and record-small Arctic ice cap, and may add to the unprecedented decline in Arctic sea ice being observed this summer.


Figure 5. An unusually strong storm formed off the coast of Alaska on August 5 and tracked into the center of the Arctic Ocean, where it slowly dissipated over the next several days. The Moderate Resolution Imaging Spectroradiometer (MODIS) on NASA's Aqua satellite captured this natural-color mosaic image on Aug. 6, 2012. The center of the storm at that date was located in the middle of the Arctic Ocean. Image credit: NASA.

Arctic storms may be increasing due to climate change
This week's Alaskan storm is the second unusually strong low pressure system to affect the Arctic in the past month. On August 4 - 8, a mighty storm with a central pressure of 963 mb raged through the Arctic, bringing strong winds that helped scatter and break up Arctic sea ice. According to a detailed post at NASA Earth Observatory, that storm was in the top 3 percent for strongest storms ever recorded north of 70 degrees latitude. A study of long-term Arctic cyclone trends authored by a team led by John Walsh and Xiangdong Zhang of the University of Alaska Fairbanks found that number and intensity of Arctic cyclones has increased during the second half of the twentieth century, particularly during the summer. Dr. Zhang explained that climate change has caused sea ice to retreat markedly in recent decades and has also warmed Arctic Ocean temperatures. Such changes may be providing more energy and moisture to support cyclone development and persistence. The strong storms of this week and a month ago would have had far less impact on the ice just a decade ago, when the sea ice was much thicker and more extensive.

A sea ice decline double-whammy
The monster Arctic storms like we've seen this year have sped up the rate of sea ice loss, but increased water temperatures and air temperatures due to human-caused global warming are the dominant reasons for the record melting of the Arctic sea ice. A July 2012 study by Day et al. found that the most influential of the possible natural influences on sea ice loss was the Atlantic Multi-decadal Oscillation (AMO). The AMO has two phases, negative (cold) and positive (warm), which impact Arctic sea ice. The negative phase tends to create sea surface temperatures in the far north Atlantic that are colder than average. In this study, the AMO only accounted for 5% - 31% of the observed September sea ice decline since 1979. The scientists concluded that given the lack of evidence that natural forces were controlling sea ice fluctuations, the majority of sea ice decline we've seen during the 1953 - 2010 period was due to human causes.

Joe Romm has a more in-depth look at the new Arctic sea ice record and what it means for the future over at climateprogess.org.

Angela Fritz and Jeff Masters

Sea Ice Climate Change

Updated: 9:28 PM GMT on September 06, 2012

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90L in the Gulf disorganized; Leslie almost stationary; Michael hits Cat 3

By: JeffMasters, 3:24 PM GMT on September 06, 2012

A remnant of Hurricane Isaac pushed southwards through Alabama on Wednesday and emerged over the Gulf of Mexico, and this disturbance is now being tracked as Invest 90L. Long-range radar out of New Orleans shows only a small area of heavy rainfall associated with 90L. The echoes show a little spiral banding behavior, and there is some slight evidence of rotation to the echoes. Visible satellite loops and surface observations from buoys and oil rigs in the Gulf suggest that 90L has formed an ill-defined, elongated surface circulation. The area covered by heavy thunderstorms is relatively small, and is pushed to the south side of the circulation center by strong northerly winds that are creating a high 20 - 30 knots of wind shear. There is a large amount of dry air that surrounds 90L on all sides that is interfering with development. A hurricane hunter aircraft is scheduled to investigate 90L this afternoon, but this flight may be cancelled if 90L does not show more organization in the next few hours.


Figure 1. Invest 90L off the coast of the Florida Panhandle as seen by NASA's Aqua satellite at 4:30 pm EDT Wednesday September 5, 2012. Image credit: NASA.

Forecast for 90L
Wind shear is predicted to fall to the moderate range, 10 - 20 knots, by tonight. Ocean temperatures in the Gulf have been cooled down considerably by the passage of Hurricane Isaac last week, and are 28.5° - 29°C. This is plenty warm enough to support formation of a tropical storm, and I expect 90L will increase in organization today and Friday as it moves slowly south-southwest. A trough of low pressure and an associated surface cold front will move southeastwards over the northern Gulf of Mexico on Sunday, and this trough should be capable of pulling 90L to the northeast to a landfall along the Florida Panhandle or west coast of Florida on Sunday. In their 8 am Tropical Weather Outlook, NHC gave 90L a 40% chance of developing into a tropical depression by Saturday morning. I put these odds a bit higher, at 50%.

Leslie remains nearly stationary
Hurricane Leslie continues to remain nearly stationary south of the island of Bermuda. Moderately high wind shear of 10 - 20 knots due to strong upper-level winds out of the west drove dry air to Leslie's west into the core of the storm last night, eroding away Leslie's eye. However, satellite loops show that Leslie is pulling a curved band of heavy thunderstorms around the west side of the center, in an attempt to form a new eye. Leslie's slow forward speed means that the storm is staying over the cold water stirred up by the storm's winds, inhibiting intensification, and NOAA buoy 41049 recorded a 1°C (1.8°F) drop in water temperature over the past 24 hours. A uncrewed Global Hawk NASA research aircraft is scheduled to fly in the stratosphere above Leslie this evening to study the hurricane's upper-level outflow. An Air Force hurricane hunter aircraft is scheduled to do a regular mission on Friday afternoon.


Figure 2. Hurricane Leslie as seen by NASA's Aqua satellite at 1:15 pm EDT Wednesday September 5, 2012. At the time, Leslie was a Category 1 hurricane with 75 mph winds. Image credit: NASA.

Forecast for Leslie
Leslie will stay stuck in a weak steering current environment until a strong trough of low pressure approaches the U.S. East Coast on Saturday. The timing of this trough is such that Leslie will be pulled northwards and then north-northeastwards over the weekend. There is significantly less agreement among the models today in the timing and speed of Leslie's track, though. The models have shifted eastwards, which lessens the threat to Bermuda and puts the island on the weak (left) side of the hurricane. If the official NHC forecast verifies, tropical storm-force winds will not begin on Bermuda until late Saturday night or early Sunday morning. According to the latest SHIPS model forecast, the shear is expected to fall to the low category, 5 - 10 knots, by Friday night. Leslie is over warm ocean waters of 29 - 30°C, and the reduction in shear and warm waters should aid intensification, and potentially allow Leslie to be at Category 2 strength at its closest pass by Bermuda Sunday morning, as indicated by the official NHC forecast. The latest 11 am EDT NHC wind probability forecast calls for a 40% chance that Leslie will be a Category 2 or stronger hurricane Sunday morning at 8 am EDT. Leslie is a huge storm, and tropical storm-force winds are expected to extend outward from its center 230 miles by Sunday.

Most of the models still indicate Leslie is likely to make landfall in Canada, but have shifted eastwards towards Newfoundland and away from Nova Scotia. The GFS model predicts a Thursday landfall in Newfoundland, but the ECMWF model is much faster, predicting a Tuesday landfall in Newfoundland. Given the wide spread in model guidance, what Leslie might do as it approaches Canada is highly uncertain. Large swells from Leslie are pounding the entire Eastern Seaboard, and these waves will increase in size as Leslie grows in size and strength this week.


Figure 3. Morning satellite image of Hurricane Michael.

Hurricane Michael hits Category 3
The first major hurricane of the 2012 Atlantic hurricane season is Hurricane Michael, which put on a unanticipated round of rapid intensification last night to become a Category 3 storm with 115 mph winds. Michael is the 7th hurricane of the season, putting 2012 in 3rd place behind 1893 and 1886 for earliest formation date of the season's 7th hurricane. We made it through 12 named storms before getting our first major hurricane, which is a rare occurrence. The only times the Atlantic has had as many as 12 named storms before getting a major hurricane was in 1936 and 1934. In both years, Hurricane 13 was the first major hurricane (note, though, that the 5th storm of 1936 is listed as a Category 3 landfall in Florida, but had maximum winds of 90 mph--definitely not Cat 3 winds--so there is a problem with the hurricane database for this storm.) Satellite loops show that Michael is an impressive storm with a well-developed eye, excellent spiral banding, and solid upper-level outflow. Michael is far out over the open Atlantic, and none of the models show that Michael will threaten any land areas during the coming seven days. Michael has likely peaked in intensity, and will not reach Category 4.

Elsewhere in the Atlantic
Most of the reliable computer models are predicting that a new tropical wave due to move off the coast of Africa on Friday will develop into a tropical depression by the middle of next week. This wave is predicted to exit Africa too far north to threaten the Lesser Antilles Islands, but it is too early to be confident of this.

I'll have a new post this afternoon.

Jeff Masters

Hurricane

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Leslie near hurricane strength; Son of Isaac (90L) emerges in the Gulf

By: JeffMasters, 3:05 PM GMT on September 05, 2012

Tropical Storm Leslie is growing more organized and is approaching hurricane strength on its slow voyage northwards at 2 mph towards the island of Bermuda. Moderately high wind shear of 15 - 20 knots due to strong upper-level winds out of the northwest continues to keep most of Leslie's heavy thunderstorms pushed to the east side of the storm, but satellite loops show that Leslie now has an impressive blow-up of heavy thunderstorms with cold cloud tops near its center. Leslie's slow forward speed means that the storm is staying over the cold water stirred up by the storm's winds, inhibiting intensification, but the waters underneath Leslie are warm to great depth, making this less of a factor than usual. According to the latest SHIPS model forecast, the shear is expected to fall steadily today, reaching the low category, 5 - 10 knots, by Thursday afternoon. Leslie is over warm ocean waters of 29 - 30°C, and the reduction in shear and warm waters should aid intensification, and potentially allow Leslie to be at Category 2 strength at its closest pass by Bermuda Saturday night and early Sunday morning, as indicated by the official NHC forecast. The latest 11 am EDT NHC wind probability forecast calls for a 48% chance that Leslie will be a Category 2 or stronger hurricane Sunday morning at 8 am EDT. Leslie is a huge storm, and tropical storm-force winds are expected to extend outward from its center 250 miles by Friday. Bermuda is likely to see a 42-hour period of tropical storm-force winds beginning Saturday morning near 2 am AST, and lasting until 8 pm AST Sunday night. The official NHC forecast shows Leslie nearly making a direct hit on Bermuda, and Leslie will be capable of bringing an extended period of hurricane-force winds lasting six or more hours to Bermuda Saturday night through Sunday morning, should a direct hit materialize. NHC is predicting that hurricane-force winds will extend outwards from the center of Leslie by 35 miles on Thursday night, and I expect this will increase to at least 60 miles by early Sunday morning, when Leslie will be making its closest pass by Bermuda.


Figure 1. Morning satellite image of Tropical Storm Leslie. Heavy thunderstorms have built near the center of the storm, and Leslie is near hurricane strength.

Leslie's impact on Canada
Leslie will stay stuck in a weak steering current environment until a strong trough of low pressure approaches the U.S. East Coast on Saturday. The timing of this trough is such that Leslie will be pulled northwards and then north-northeastwards over the weekend. There are still significant differences among the models in the timing and speed of Leslie's track over the weekend, but we can now dismiss the threat of Leslie making a direct hit on New England. The storm is likely to make landfall in Nova Scotia or Newfoundland, though there are significant differences in the models' predictions of the timing of Leslie's arrival in Canada. The GFS model predicts an early Tuesday landfall in Newfoundland, but the ECMWF model is much faster and farther west, predicting a Monday afternoon landfall in Nova Scotia. Large swells from Leslie are pounding the entire Eastern Seaboard, and these waves will increase in size as Leslie grows in strength this week. The Hurricane Hunters are scheduled to make their first flight into Leslie on Thursday afternoon.


Figure 2. Morning radar image of Invest 90L off the coast of the Florida Panhandle.

Son of Isaac: Invest 90L emerges in the Gulf of Mexico
During Tropical Depression Isaac's trek across the center of the U.S. during the Labor Day weekend, the storm was ripped in half. One portion of the storm moved over the Northeast U.S., bringing heavy rains there, and another portion sank southwards over Alabama. You can see this split by studying an animation of the vorticity at 850 mb (the amount of spin at low levels of the atmosphere, near 5,000 feet above sea level) from the University of Wisconsin. This remnant of Isaac, which still maintained some of Isaac's spin, brought heavy rains of 5 - 10 inches that caused flooding problems over portions of Alabama on Tuesday. The storm has now emerged over the Gulf of Mexico near the Florida Panhandle, and was designated Invest 90L this morning by NHC. In their 8 am Tropical Weather Outlook, NHC gave 90L a 20% chance of developing into a tropical depression by Friday morning. According to NHC naming rules, "if the remnant of a tropical cyclone redevelops into a tropical cyclone, it is assigned its original number or name". Since "the remnant" refers to the primary remnant, and 90L does not fit the definition of a "primary remnant", the storm will be given a new name should it develop into a tropical storm, according to information posted on the NHC Facebook page. Esau or Jacob--the names of the sons of the biblical Isaac--would be fitting names for 90L, but the next storm on the list of Atlantic storms is Nadine.

Long-range radar out of Mobile, Alabama shows a large area of heavy rainfall along the coast due to 90L. The echoes do show some spiral banding behavior, but there is only a slight evidence of rotation to the storm. Infrared satellite loops show that the thunderstorms associated with 90L are not that vigorous and do not have particularly cold cloud tops, and the area covered by the thunderstorms is relatively small. Wind shear is a high 20 - 30 knots over the northern Gulf of Mexico, but is predicted to fall to the moderate range, 10 - 20 knots, by Thursday afternoon. Ocean temperatures in the Gulf have been cooled down considerably by the passage of Hurricane Isaac last week, and are 28 - 28.5°C. This is still plenty warm enough to support formation of a tropical storm, and I expect 90L will increase in organization on Thursday and Friday as it moves slowly south or south-southwest. 90L could become a tropical depression as early as Thursday, though Friday is more likely. A hurricane hunter aircraft is scheduled to investigate 90L on Thursday afternoon. A trough of low pressure and an associated surface cold front will move southeastwards over the northern Gulf of Mexico on Sunday, and this trough should be capable of pulling 90L to the northeast to a landfall along the Florida Panhandle or west coast of Florida on Sunday.


Figure 3. Morning satellite image of Tropical Storm Michael.

Tropical Storm Michael in the Central Atlantic
Tropical Storm Michael has strengthened to 50 mph winds, and appears to have a favorable enough environment to become a hurricane later this week. Satellite loops show that this is a small tropical cyclone, far out over the open Atlantic, and none of the models show that Michael will threaten any land areas.

Elsewhere in the Atlantic
The GFS and ECMWF models are predicting that a new tropical wave due to move off the coast of Africa on Friday will develop into a tropical depression by the middle of next week. It's too early to tell if this system might threaten the Lesser Antilles Islands.

Jeff Masters

Hurricane

Updated: 3:18 PM GMT on September 05, 2012

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Leslie headed towards Bermuda; Tropical Storm Michael forms

By: JeffMasters, 3:01 PM GMT on September 04, 2012

Tropical Storm Leslie continues to suffer from moderately high wind shear of 15 - 20 knots, due to strong upper-level winds out of the northwest. The shear is keeping heavy thunderstorms confined to the southeast quadrant of the storm. Satellite loops show that Leslie has almost no heavy thunderstorm activity near its center, and the storm is crawling north at walking pace, 3 mph. Leslie's slow forward speed means that the storm is staying over the cold water stirred up by the storm's winds, inhibiting intensification. According to the latest SHIPS model forecast, the shear is expected to stay moderately high through Tuesday night, then drop to the low category, 5 - 10 knots, by Thursday afternoon. At that time, Leslie will be over warm ocean waters of 29 - 30°C, and the reduction in shear and warm waters should aid intensification. However, Leslie's motion will continue to be slow, keeping the storm over its cool water wake, and keeping any intensification slow. Once Leslie begins moving more quickly on Saturday, this effect will diminish, and Leslie could be at Category 2 strength on Sunday morning, as indicated in the official NHC forecast. Steering currents for Leslie are expected to be weak through Friday, as Leslie is stuck between two upper level lows. The latest guidance from our top computer models continues to show Leslie making a very close pass by Bermuda on Saturday. Leslie is a huge storm, and tropical storm-force winds are expected to extend outward from its center 250 miles by Friday. Bermuda is likely to see a 48-hour period of tropical storm-force winds beginning Friday night that lasts until Sunday night. The official NHC forecast shows Leslie nearly making a direct hit on Bermuda, but the uncertainty in 4-day NHC forecasts is around 200 miles. Thus, the latest 11 am EDT NHC wind probability forecast calls for just a 12% chance of hurricane force winds on Bermuda on Saturday. Nevertheless, Leslie is capable of bringing an extended period of hurricane-force winds lasting six or more hours to Bermuda Saturday night through Sunday morning, should a direct hit materialize.


Figure 1. Morning satellite image of Tropical Storm Leslie. The low-level circulation center has very little in the way of heavy thunderstorms surrounding it, thanks to strong northwest winds creating 15 - 20 knots of wind shear.

Leslie will stay stuck in a weak steering current environment until a strong trough of low pressure approaches the U.S. East Coast on Saturday. This trough should be strong enough to pull Leslie quickly to the north on Saturday and Sunday, and Leslie may be close enough to the coast that the storm will make landfall in Nova Scotia or Newfoundland, Canada on Monday, September 10. None of the reliable models have shown that a direct hit on New England will occur, but we can't rule that possibility out yet. The storm may also miss land entirely, and brush by the coasts of Nova Scotia and Newfoundland. Large swells from Leslie reached Cape Hatteras, North Carolina last night, and will begin pounding the entire Eastern Seaboard today through Sunday. These waves will be capable of causing significant beach erosion and dangerous rip currents. The Hurricane Hunters are scheduled to make their first flight into Leslie on Wednesday afternoon.


Figure 2. Morning satellite image of Tropical Storm Michael.

Tropical Storm Michael forms in the Central Atlantic
Tropical Storm Michael has formed in the Central Atlantic on Monday, but is not destined for fame. Satellite loops show that this is a very small tropical cyclone, and the storm is well away from any land areas. Michael is under moderately high shear of 15 - 20 knots, and this shear is forecast to remain at 15 - 20 knots through Wednesday. Since Michael is such a small storm, just a modest increase in shear could destroy it. But if Michael survives until Thursday, when shear is expected to fall to the low range, it has the opportunity to strengthen.

Michaels's formation on September 4 puts 2012 in third place for earliest formation date of the season's thirteenth storm. The record is held jointly by 2005, which had Hurricane Maria form on September 2, and 2011, which had Tropical Storm Lee form on September 2 (there was an unnamed tropical storm that year before Lee.) None of the models show that Michael will threaten any land areas. Michael is a classic example of the type of storm that likely would have been missed before the advent of satellites, since the storm is small, far from land, and may be short-lived.

Jeff Masters

Hurricane

Updated: 3:03 PM GMT on September 04, 2012

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Disorganized Leslie headed towards Bermuda

By: JeffMasters, 4:18 PM GMT on September 03, 2012

Tropical Storm Leslie continues to struggle with moderately high wind shear of 15 - 20 knots, due to strong upper-level winds out of the northwest. The shear is keeping heavy thunderstorms confined to the southeast quadrant of the storm. These thunderstorms are as far removed from the center as we've so far with Leslie, as seen on satellite loops. According to the latest SHIPS model forecast, the shear is expected to stay moderately high through Tuesday night, then drop to the low category, 5 - 10 knots, by Wednesday night. At that time, Leslie will be over warm ocean waters of 29°C, and the reduction in shear and warm waters should allow Leslie to intensify into at least a Category 1 hurricane by Friday, as predicted by most of the intensity forecast models. Intensification to a stronger storm may be hampered by its slow motion, which will cause Leslie to churn up cool water from the depths that will slow intensification. Once Leslie begins moving more quickly on Saturday, this effect will diminish, and Leslie could be at Category 2 strength on Saturday, as predicted by the HWRF and LGEM models. Steering currents for Leslie are expected to be weak on Tuesday - Friday, as Leslie gets stuck between two upper level lows. The latest guidance from our top computer continues to show Leslie making a very close pass by Bermuda on Saturday, and that island can expect a 3-day period of rough weather Friday through Sunday. Leslie will stay stuck in a weak steering current environment until a strong trough of low pressure approaches the U.S. East Coast on Saturday. This trough should be strong enough to pull Leslie quickly to the north on Saturday and Sunday, and Leslie may be close enough to the coast that the storm will make landfall in Canada on Monday, September 10. None of the reliable models have shown that a direct hit on New England will occur, but we can't rule that possibility out yet. The most likely long-term fate of Leslie will be for it to miss land entirely and brush by the coasts of Nova Scotia and Newfoundland, but any forecast of what a tropical cyclone might do a full seven days in advance is pretty speculative. Regardless, Leslie will bring an extended period of high waves to Bermuda, the U.S. East Coast, and Nova Scotia and Newfoundland this week. These waves will be capable of causing significant beach erosion and dangerous rip currents.


Figure 1. Morning satellite image of Tropical Storm Leslie. The low-level circulation center is fully exposed to view, thanks to strong northwest winds creating 15 - 20 knots of wind shear.

Invest 99L in the Central Atlantic
A small extratropical low pressure system that got cut off from the jet stream and is now spinning away in the Central Atlantic, near 26°N 42°W, (Invest 99L), is headed west at 10 mph, and has developed a small amount of heavy thunderstorm activity. This storm is not a threat to any land areas, and in their 8 am EDT Tropical Weather Outlook on Monday, NHC gave 99L a 30% chance of developing into a tropical cyclone by Wednesday morning.

Jeff Masters

Hurricane

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Leslie a threat to Bermuda; Isaac is gone

By: JeffMasters, 4:30 PM GMT on September 02, 2012

Tropical Storm Leslie is struggling today under a high 20 knots of wind shear, due to strong upper-level winds out of the northwest. The high shear is keeping heavy thunderstorms confined to the southeast quadrant of the storm, as seen on satellite loops. According to the latest SHIPS model forecast, the shear is expected to stay high through Wednesday, then drop to the low category, 5 - 10 knots, on Thursday and Friday. At that time, Leslie will be over warm ocean waters of 29°C, and may intensify to a hurricane by Friday, as predicted by most of the intensity forecast models. Steering currents for Leslie are expected to collapse by mid-week, as Leslie gets stuck between two upper level lows. The storm will slowly meander over the open ocean for many days, and the latest guidance from the GFS and ECMWF models shows Leslie making a very close pass by Bermuda on Saturday, and that island can expect a 3-day period of rough weather Friday through Sunday. Leslie will stay stuck in a weak steering current environment until a strong trough of low pressure approaches the U.S. East Coast on Saturday. This trough should be strong enough to pull Leslie to the north by Sunday, September 9. At that time, Leslie may be close enough to the coast that the storm will make landfall in Canada or New England by Monday, September 10. However, making forecasts of what a tropical cyclone might do a week in advance is a sketchy proposition. Leslie could miss land entirely; this all depends upon the timing and strength of the September 8 trough of low pressure. If Leslie survives its encounter with high wind shear early this week and becomes a hurricane late in the week, the storm will bring an extended period of high waves to the U.S. coast late this week. These waves will be capable of creating dangerous rip currents and beach erosion.


Figure 1. Morning satellite image of Tropical Storm Leslie.

Invest 99L in the Central Atlantic
An extratropical low pressure system that got cut off from the jet stream and is now spinning away in the Central Atlantic near 28°N 38°W has begun to develop a small amount of heavy thunderstorm activity, and was designated Invest 99L by NHC on Sunday morning. This storm is not a threat to any land areas, and in their 8 am EDT Tropical Weather Outlook on Sunday, NHC gave 99L a 10% chance of developing into a tropical cyclone by Tuesday morning.

Isaac declared non-tropical
Hurricane Isaac's remnants are no longer considered an organized tropical system, but ex-Isaac will bring 1 - 3" of rain to Indiana, Kentucky, and Tennessee today. Isaac's remnants may bring a few tornadoes to Tennessee, Alabama, and Mississippi today, and NOAA's Storm Prediction Center has placed portions of these states in their "Slight Risk" area for severe weather. As of late Saturday night, Isaac's preliminary tornado total was 39, putting it in a tie for 12th place for most tornadoes spawned by a tropical system, according to Dr. Greg Forbes of the Weather Channel. The record holder is Hurricane Ivan of 2004, with 127 tornadoes. Isaac brought storm surges as high as 13.6' to the coast (in Lake Borgne, LA), and dumped 20" of rain at one station in New Orleans. Isaac is being blamed for at least seven deaths in the U.S., 24 in Haiti, and five in the Dominican Republic.

A few notable rainfall totals from Isaac, through Saturday:

20.08" New Orleans, LA
17.63 Wilmer, AL
17.04" Kiln, MS
16.60" Vero Beach, FL
16.29" Royal Palm Beach, FL
15.02" Marion, MS
13.99" Pascagoula, MS
13.94" Baptist, LA
13.45" Hattiesburg, MS
10.85" Gulfport, MS
10.40" Slidell, LA
10.17" Biloxi, MS
9.85" Mobile, AL
9.08" Mount Pleasant, SC
8.64" West Palm Beach, FL
8.39" Pine Bluff, AR
7.36" Charleston, SC (2.8 mi NE)
5.95" Baton Rouge, LA
5.63" Greenville, IL


Figure 2. Rainfall total for Hurricane Isaac, ending at 8 am EDT Sunday September 2, 2012. Over ten inches of rain fell in portions of Louisiana, Mississippi, Alabama, Florida, and Arkansas. Image credit: NOAA/AHPS.

I'll have a short post on Monday.

Jeff Masters

Hurricane

Updated: 7:14 PM GMT on September 02, 2012

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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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