Preparedness & Recovery

Experimental Storm-Surge Maps to Accompany NOAA Hurricane Projections

Emergency managers will have another tool to help them protect low-lying areas from flooding the next time a hurricane approaches.

by Matt McNab, McClatchy News / February 6, 2014
Several homes along the beach in Oak Island, N.C., were damaged by hurricane-force winds and high water in October 1999. Photo courtesy of Dave Saville/FEMA

Emergency management crews will have another tool to help them protect low-lying areas from flooding the next time a hurricane approaches.

Beginning this year, the National Hurricane Center's projections will include surge maps that show where flooding is expected along the Gulf and Atlantic coasts.

Flooding that usually accompanies a hurricane is caused by a storm surge -- a rise in ocean water caused by the atmospheric pressure and wind that pushes water landward. Storm surges can kill, with nine out of every 10 deaths from hurricanes caused by the surge or its flooding, according to Federal Emergency Management Agency statistics.

The surge maps, which will be experimental for at least two years, will be issued at the first sign of a hurricane or tropical storm watch and will be continuously updated with each new hurricane forecast, typically issued every six hours, according to a release from hurricane center's parent agency, the National Oceanic and Atmospheric Administration.

Surge maps will be color-coded to show areas where flooding is expected and its depth. The depth projections will show the worst case scenario, with a 10 percent chance the levels could be exceeded, the release said.

In South Carolina, Town of Hilton Head Island emergency management coordinator Thomas Dunn said the maps will help. Maps his division currently uses to estimate flood levels are based on the category of a hurricane, which is calculated by wind speed, not surge or flooding levels.

Those maps show the worst case scenario for each category, without taking into account the unique properties of individual storms, Dunn said.

Dunn first heard about the maps while attending a course at the National Hurricane Center, when the maps were still being tested.

The Lowcountry has been hit hard by storm surges in the past. In 1989, Hurricane Hugo brought surges of almost 20 feet to the South Carolina coast. In 1893, between 1,000 and 2,000 people were killed when a hurricane hit the Sea Islands, including those in Beaufort County. Most deaths were caused by storm surge.

In Beaufort County, many major evacuation routes — U.S. 278, U.S. 21, and U.S. 17 — could flood before everyone is safely out of the county, according to a 2011 study that showed elevations in certain areas are lower than originally thought. County officials have said they would recommend evacuations for any storm rated a Category 1 or stronger.

(c)2014 The Island Packet (Hilton Head, S.C.)