Coastal Services Center

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Frequently Asked Questions (FAQ)

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This page provides frequently asked questions about and answers to hurricane evacuation studies, evacuation zone data, storm surge data, and shelters. Follow the links below to access the answers.

Where does the evacuation zone data come from and what does it mean?

What are Hurricane Evacuation Studies?

Where does the storm surge data come from and what does it mean?

What do the different storm surge zones mean for me?

What is storm surge?

Where does the storm surge data come from?

How accurate is the storm surge data?

What is the difference between an evacuation zone and a storm surge zone?

Where can I get more information about hurricane shelters in my area?

Where can I find information about what roads to take during an evacuation?

What do I do if there is an evacuation order issued for my area?

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Questions and Answers

Question: Where does the evacuation zone data come from and what does it mean?

Answer:
Hurricane evacuation zones are usually determined as part of your state's Hurricane Evacuation Study (HES). While some states use storm surge zones as a guide, others use easily recognizable roadways such as interstates and highways to determine evacuation zones. The HES is conducted jointly by the Federal Emergency Management Agency (FEMA), the U.S. Army Corps of Engineers (USACE), the National Oceanic and Atmospheric Administration (NOAA), and your state emergency management agency. Close coordination between these (and other) agencies facilitates more effective responses at the local level to hurricane emergencies. Depending on your proximity to the coast, you may or may not be located in an evacuation zone. The closer you are to the coast, the more likely it is that you will be located in an evacuation zone. If you are located in an evacuation zone, it is important to note that the particular zone you are in will not necessarily match the particular storm surge zone you are in. For safety reasons, officials typically issue evacuations for one category storm higher than what they are expecting. For example, if there is a category one hurricane approaching but you live in a category three evacuation zone, you may still be asked to leave, simply due to uncertainties associated with the storm's track and intensity. Always follow the instructions of local officials before, during, and after an emergency.

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Question: What are Hurricane Evacuation Studies?

Answer:
Hurricane Evacuation Studies are designed to assist state and local governments in the development and/or enhancement of hurricane planning by providing the best technical information available. Typically, a study includes five related analyses that develop data concerning hurricane hazards, vulnerability of the population, assumptions about public response to evacuation advisories, evacuation network clearance times, and sheltering needs for various hurricane threat situations. The results from these studies include storm surge analyses and evacuation requirements for hurricanes of different intensities and that come from different directions. Emergency planners use the information in the HES to devise checklists of steps to take during a hurricane. Following these checklists, decision makers can determine what to do when certain meteorological conditions are met or forecasted, based mostly on information from the National Hurricane Center and local National Weather Service weather forecast offices. The overall objective of an HES is to provide emergency management officials with state-of-the-art information on the major factors affecting hurricane evacuation planning and decision making, and the skills and training aids necessary to educate the public. Visit the USACE National Hurricane Study Program Web Site for more information.

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Question: Where does the storm surge data come from and what does it mean?

Answer:
The storm surge zones data used in this application were generated using the Sea, Lake, and Overland Surges from Hurricanes (SLOSH) model. SLOSH is a computerized model run by the National Weather Service to estimate storm surge heights resulting from historical, hypothetical, or predicted hurricanes. The model creates its estimates by assessing the pressure, size, forward speed, track, and wind data from a storm. Graphical output from the model displays color-coded storm surge heights for a particular area. The calculations are applied to a specific locale's shoreline, incorporating the unique bay and river configurations, water depths, bridges, roads, and other physical features.

It is important to note that storm surge maps reflect the worst case hurricane storm surge inundation (including astronomical high tide), regardless of the point of where the center of the hurricane (or tropical storm) makes landfall. No single hurricane will necessarily cause all of the flooding represented on the maps. It should also be noted that the data reflect only still-water saltwater flooding and do not take into account the effects of pounding waves that ride on top of the storm surge in locations exposed to wave action. Also, these maps do not show areas that may be flooded by excessive rainfall-they only depict flooding that would occur as a result of the ocean level rising (as well as estuaries and rivers that can be affected by hurricane storm surge) and inundating the color-coded areas.

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Question: What do the different storm surge zones mean for me?

Answer:
Hurricanes are classified by categories according to the Saffir-Simpson Hurricane Scale. The scale ranges from 1 to 5, with the "weakest" storms classified as category 1 (74 to 95 miles per hour sustained winds) and the strongest storms as category 5 (sustained winds greater than 155 miles per hour). The different storm surge zone categories imply that flooding is possible for your area for a storm of that category OR HIGHER. For example, a category 3 storm surge zone would be most vulnerable to storms of category 3 and higher. Similarly, those people that live in category 1 storm surge zones are vulnerable to all categories of storm, from 1 up to 5. Always remember that local officials make decisions about who should stay and who should go, so be sure to listen to and follow their advice if a storm is threatening your area. You can use the Hurricane Storm Surge Potential Threat Matrix to determine your potential risk to storm surge according to which evacuation zone you are located in.

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Question: What is storm surge?

Answer:
Storm surge is simply water that is pushed toward the shore by the force of the winds swirling around a storm. This advancing surge combines with the normal tides to create the hurricane storm tide, which can increase the mean water level 15 feet or more. In addition, wind-driven waves are superimposed on the storm tide. This rise in water level can cause severe flooding in coastal areas, particularly when the storm tide coincides with the normal high tides. Because much of the United States' densely populated Atlantic and Gulf coastlines lie less than 10 feet above mean sea level, the danger from storm tides is tremendous.

The Saffir-Simpson Hurricane Scale provides general estimates of potential storm surge heights relative to the five different categories of hurricanes. However, the level of surge in a particular area, when all other factors are held constant, is in large part determined by the slope of the continental shelf. For instance, a shallow continental shelf (see image below) off the coast will allow a greater surge to inundate coastal communities. Communities with a steeper continental shelf (see image below) will not see as much surge inundation, although large breaking waves can still present major problems. Storm tides, waves, and currents in confined harbors can severely damage ships, marinas, and pleasure boats.

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Question: Where does the storm surge data come from?

Answer:
One tool used to evaluate the threat from storm surge is the Sea, Lake, and Overland Surges from Hurricanes (SLOSH) model. SLOSH is a computerized model run by the National Weather Service to estimate storm surge heights resulting from historical, hypothetical, or predicted hurricanes. The model creates its estimates by assessing the pressure, size, forward speed, track, and wind data from a storm. Graphical output from the model displays color-coded storm surge heights for a particular area. The calculations are applied to a specific locale's shoreline, incorporating the unique bay and river configurations, water depths, bridges, roads, and other physical features.

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Question: How accurate is the storm surge data?

Answer:
The SLOSH model is generally accurate within 20 percent. For example, if the model calculates a peak 10-foot storm surge for the hurricane, you can expect the observed peak to range from 8 to 12 feet. The model accounts for astronomical tides (which can add significantly to the water height) by specifying an initial tide level, but does not include rainfall amounts, riverflow, or wind-driven waves. However, this information is combined with the model results in the final analysis of at-risk areas. The point of a hurricane's landfall is crucial to determining which areas will be inundated by the storm surge. Where the hurricane forecast track is inaccurate, SLOSH model results will be inaccurate. The SLOSH model, therefore, is best used for defining the potential maximum surge for a location. Visit the National Hurricane Preparedness Week Web site for more information on storm surge and the SLOSH model.

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Question: What is the difference between an evacuation zone and a storm surge zone?

Answer:
Storm surge zones indicate areas subject to flooding from different categories of hurricane. Evacuation zones are areas, typically located within or in close proximity to storm surge zones. Emergency management officials use evacuation zone information to determine who needs to evacuate before a hurricane makes landfall. By becoming familiar with what zone you are located in, you can be better prepared to execute your plan when or if an evacuation order is issued for the zone in which you live.

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Question: Where can I get more information about hurricane shelters in my area?

Answer:
There are many places to access information about shelters in your area. The best place to start is your state or local emergency management office or you can contact your local office of the American Red Cross.

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Question: Where can I find information about what roads to take during an evacuation?

Answer:
In most cases, your state's Department of Transportation determines which roads will serve as evacuation routes during emergencies. This information is typically available from the Department's Web site in the form of maps. Visit your state's Department of Transportation or Emergency Management office to learn more. The Evacuation Zone Maps tool also provides the ability to view hurricane evacuation routes, although these data are not currently available for all areas.

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Question: What do I do if there is an evacuation order issued for my area?

Answer:
Evacuations are necessary to protect people from the potential life-threatening effects of hazards. Hurricane evacuations are typically focused on individuals living in "low-lying" areas. Typically, these are areas located immediately adjacent to or within close proximity to the coast or a major coastal waterway. Evacuations are focused in these areas because the greatest risk to life from a hurricane comes from water – both storm surge and breaking waves along the immediate coast and flooding caused by heavy rains away from the coast. Anyone living in a manufactured home will be asked to evacuate, as these structures are not designed to withstand the very strong winds that accompany a hurricane. If you do not live in a manufactured home and live away from the coast and/or a major coastal waterway, you may be urged to "Hide from the Wind" or, essentially, stay put. If this is the case, and you feel that your residence is "wind-worthy," the best place to be is in a walk-in closet, bathroom, or inner hallway away from windows and doors.

If you must evacuate, seek shelter in a sturdy building located inland from the coast, such as a masonry or wood-frame building or hotel, or an officially designated American Red Cross shelter. If you plan to evacuate, particularly if you are not ordered to do so, leave early so that you don't impede carefully planned evacuation procedures that plan for a certain number of cars occupying crowded roadways before a storm. Evacuations are planned well in advance and include "clearance time," which is the time it takes for all evacuees to reach a safe destination and to clear the roadways in advance of a storm. The bottom line is to make sure you have a plan – know what you're going to do and where you're going to go if an evacuation order is issued. Visit the DisasterHelp Web site for more information on disaster preparedness.

In the event that an evacuation order is issued for your area, consider the following:

• Stay alert to storm advisories; know the difference between a hurricane watch and warning.
• Enact your family disaster plan.
• Map out your evacuation route – use travel routes specified by local authorities. DO NOT get on the road without a place to go.
• Fill your car with gasoline.
• Evacuate if told to do so – DO NOT get stranded. EVACUATE EARLY. If possible, evacuate to the home of either friends or family in a non-vulnerable area within your county. Next, try a motel or hotel and, as a last resort, go to a public shelter. Remember, shelters are not designed for comfort and do not usually accept pets.
• Enact your pet plan. Before a storm threatens, contact your veterinarian or local humane society for information on preparing your pets for an emergency.
• Bring your disaster supply kit, including important documents.
• Secure your home before leaving. Board up windows and glass doors, anchor loose yard objects or bring them inside and lock your doors.
• Get cash. Following a hurricane, banks and ATMs may be temporarily closed.
• Notify family and friends of your plans.
• People who require special assistance in evacuating should register with their local emergency management office.

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