Storm Surge Risk Maps: Methodology

Posted: 20-Jul-2006; Updated: 16-Aug-2006

The data used to generate the maps of Florida are published by the National Oceanic and Atmospheric Administration on its Coastal Risk Atlas web site. The data used to generate the maps of South Carolina are from the South Carolina Hazards research lab project on coastal vulnerability and is available here. The data used to generate the maps of North Carolina are from the North Carolina Corporate Geographic Database and is available here The data used to generate the maps of Virginia were developed by the U.S. Army Corps of Engineers for the City of Norfolk, VA, office of Emergency Preparedness and Response.

The extent of flooding shown on these maps is illustrative and based on worst-case scenario data generated by SLOSH – the Sea, Lake and Overland Surges from Hurricanes computer model.  Hundreds of hypothetical hurricanes are simulated for various storm categories, storm speeds, landfall directions, and landfall locations, to generate the data used in these maps.

SLOSH is used by federal and state agencies to estimate storm surge heights and winds resulting from historical, hypothetical, or predicted hurricanes.  Variables incorporated into the SLOSH model include five storm factors – wind speed, central pressure, the size, forward speed, and the track direction of the hurricane.  It also incorporates factors specific for each locale, such as unique bay and river configurations, water depths, bridges, roads and other physical features.

For an actual hurricane, these factors play a critical roll in determining the true extent of possible flooding. The point of a hurricane's landfall, in particular, 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.

Storm categories refer to intensity based on the Saffir-Simpson Hurricane Scale. For more information about the scale visit the National Hurricane Center's web site.