Hurricane and Tropical Cyclones

Storm Surge Basics

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By Jeffrey Masters, Ph.D. — Director of Meteorology, Weather Underground, Inc.

Welcome to the Weather Underground storm surge pages! Before accessing our storm surge inundation maps for the U.S. coast, we recommend you familiarize yourself with how to interpret these images by reading on. If you live near the ocean, the storm surge is the most dangerous part of a hurricane's hazards. The high death tolls of the ten deadliest U.S. hurricane disasters, including the Galveston Hurricane of 1900 (over 8000 killed), the Lake Okeechobee Hurricane of 1928 (2500 killed), and Hurricane Katrina of 2005 (1833 killed), were primarily due to the storm surge. The storm surge is water that is pushed onto shore by a hurricane. It is rarely a "wall of water" as often claimed, but rather a rise of water that can be as rapid as several feet in just a few minutes. The storm surge moves with the forward speed of the hurricane--typically 10 - 15 mph. This wind-driven water moving at 10 - 15 mph has tremendous power. A cubic yard of sea water weighs 1,728 pounds--almost a ton. A one-foot deep storm surge can sweep your car off the road, and it is difficult to stand in a six-inch surge. Compounding the destructive power of the rushing water is the large amount of floating debris that typically accompanies the surge. Trees, pieces of buildings, and other debris float on top of the storm surge and act as battering rams that can cave in any buildings unfortunate enough to stand in the way. If you receive an evacuation order for a hurricane storm surge, it is a very good idea to get out sooner rather than later. The storm surge can begin to rise a day before the storm hits, cutting off escape routes when low-lying highways are flooded. This is particularly true along the Gulf of Mexico shore.

Figure 1

Figure 1. Hurricane Katrina's storm surge pours over the 8-foot high north levee of the MRGO/Intra-Coastal Canal, directly under the Paris Road Bridge in eastern New Orleans. The photo was taken by Dan McClosky, the manager of Entergy's Michoud Power Plant. According to an interview at wwltv.com, "there were waves up on top of that, that were probably 15 to 18 foot on top of what you saw from the hurricane protection levee that was out there," McClosky said. Mike Collins of Austin, Texas has put together a nice in-depth description of this photo, which was judged as being authentic on the hoax debunking web site snopes.com.

The storm surge is created by wind, waves, and low pressure

There are three mechanisms that contribute to the storm surge:

  1. The action of the winds piling up water (typically more than 85% of the surge).
  2. Waves pushing water inland faster than it can drain off. This is called wave set-up. Wave set-up is typically 5 - 10% of the surge.
  3. The low pressure of a hurricane sucking water higher into the air near the eye (typically 5 - 10% of the surge).

The storm surge depends greatly upon the size and intensity of a hurricane, the angle that it approaches the shore at, how deep the water is close to shore (the slope of the seabed at the coastline), and how fast the hurricane is moving. This is discussed in much more detail in our web pages, A detailed view of the storm surge: comparing Katrina to Camille, and General characteristics of storm surges.

Figure 2

Figure 2. Depiction of a fifteen foot hurricane storm surge occurring at high tide of two feet about mean sea level, creating a seventeen foot storm tide. Note that there are 10-foot waves on top of the 17-foot storm tide, so the external high water mark (HWM) left on the outside of structures by this hurricane could be 27 feet or higher. Image credit: NOAA SLOSH Display Training Manual (PDF File).

Definitions: storm tide, storm surge, high water mark

The storm surge is how high above current sea level the ocean water gets. The number we are most interested in regarding storm surge is how many feet above mean sea level (MSL) inundation will occur. This number is the storm tide, not the storm surge. The storm tide is the height of the storm surge above mean sea level (MSL), corrected for the tide. For example, in a location where high tide is two feet higher than mean sea level, and low tide is two feet lower than mean sea level, a 15-foot storm surge would cause a 17-foot storm tide if the hurricane hit at high tide or a 13-foot storm tide at low tide. Keep in mind that on top of the storm surge will be large waves capable of causing severe flooding and battering damage, and these waves are not included in storm surge forecasts. The waves on top of the storm tide break when they reach shallow water, and create an external high water mark (HWM) on structures. The high water mark can be much higher than the storm surge or storm tide. For example, the maximum storm surge of Hurricane Katrina was 27.8 feet in Pass Christian, MS (measured inside a building where waves couldn't reach). However, the highest high water mark was much higher--34.1 feet on the outside of a building in Biloxi, MS, where a high tide of about 1 foot combined with 11-foot high waves on top of the 22-foot storm surge to create the 34.1 foot high water mark.

Figure 3

Figure 3. High water marks on East Ship Island, Mississippi, after Hurricane Katrina in 2005. Left: Bark stripped off a tree with salt-burned pine trees in the background (note the 25 ft (7.65 m) long survey rod for scale). Right: Massive beach and over wash erosion illustrated by damaged and snapped pine trees along the beach. Arrows show the the high water mark left by the storm surge. Image credit: Fritz et al., 2007, "Hurricane Katrina storm surge distribution and field observations on the Mississippi Barrier Islands" (PDF File), Estuarine, Coastal, and Shelf Science (2007), doi:10.1016/j.ecss.2007.03.015.

Weather Underground Storm Surge Articles

Storm Surge Safety Actions

  • Minimize the distance you must travel to reach a safe location; the further you drive the higher the likelihood of encountering traffic congestion and other problems on the roadways.

  • Select the nearest possible evacuation destination, preferably within your local area, and map out your route. Do not get on the road without a planned route, or a place to go.

  • Choose the home of the closest friend or relative outside a designated evacuation zone and discuss your plan with them before hurricane season.

  • You may also choose a hotel/motel outside of the vulnerable area.

  • If neither of these options is available, consider the closest possible public shelter, preferably within your local area.

  • Use the evacuation routes designated by authorities and, if possible, become familiar with your route by driving it before an evacuation order is issued.

  • Contact your local emergency management office to register or get information regarding anyone in your household whom may require special assistance in order to evacuate.

  • Prepare a separate pet plan, most public shelters do not accept pets.

  • Prepare your home prior to leaving by boarding up doors and windows, securing or moving indoors all yard objects, and turning off all utilities.

  • Before leaving, fill your car with gas and withdraw extra money from the ATM.

  • Take all prescription medicines and special medical items, such as glasses and diapers.

  • If your family evacuation plan includes an RV, boat or trailer, leave early. Do not wait until the evacuation order or exodus is well underway to start your trip.

  • If you live in an evacuation zone and are ordered to evacuate by state or local officials, do so as quickly as possible. Do not wait or delay your departure, to do so will only increase your chances of being stuck in traffic, or even worse, not being able to get out at all.

  • Expect traffic congestion and delays during evacuations. Expect and plan for significantly longer travel times than normal to reach your family's intended destination.

  • Stay tuned to a local radio or television station and listen carefully for any advisories or specific instructions from local officials. Monitor your NOAA Weather Radio.

Source: NOAA

Hurricane Preparedness

National Hurricane Center

Centers for Disease Control & Prevention