While winds from a hurricane can be impressive, residents should be more concerned with a hurricane’s potential storm surge.
Storm surges account for about half of the people killed by tropical storms in the United States, according to the National Oceanic and Atmospheric Administration.
In an effort to give coastal residents better information about the threat, the National Weather Service has a number of ways to convey the risk.
More than 48 hours before a storm, the Weather Service begins to run computer models that look at worst-case scenarios for storm surge in a coastal area.
This year, however, the National Weather Service is unveiling a new model that takes the actual hurricane forecast along with information from past storms to come up with a more accurate prediction of storm surge, said Ken Graham, meteorologist in charge for the National Weather Service’s Slidell Office.
This will be the first time forecasters will be able to show an expected storm surge displayed as water actually above ground level.
In the past, forecasters could predict how much water was coming in, but it meant very little to a homeowner or business owner unless he knew the elevation of his property. If forecasters estimated a storm surge was going to be 12 feet, that may have given a homeowner pause.
But if his house sat on land that had an elevation of 14 feet, it wouldn’t touch the house anyway. If his house sat on land with an elevation of 2 feet, he was going to get about 10 feet of water.
All of these models provide information needed for planning and action in advance of a storm, but there are still limitations to the science, Graham said.
The drawback to the new model is that it can only be run two days before a hurricane is expected to make landfall and response decisions have to be made before then.
In addition, the maps show areas behind levees, like New Orleans and lower Lafourche Parish, as just hash marks.
The hash marks don’t mean flooding isn’t possible, Graham said; they just mean the model can’t calculate it because there are so many moving parts in a levee system.
“The biggest fear I have is misinterpretation of this,” Graham said, pointing at the hash marks over New Orleans in the model graphic.
Graham said he’s been promoting the message that people living inside these levee areas need to pay attention to instruction from emergency officials before a storm.
As the National Weather Service looks to find new ways to communicate storm surge risk, others are looking for lessons to be learned from the past.
Researchers Barry Keim, state climatologist at LSU, and Hal Needham, program manager for the Southern Climate Impacts Planning Program with LSU, have created SURGEDAT, a worldwide storm surge data center.
So far, the ever expanding website includes 700 storms around the world dating back to 1880, of which more than 350 storms were in the United States.
According to information gathered so far, the Gulf of Mexico is No. 2 in the world for having the highest storm surges, only behind the Bay of Bengal in India, and No. 2 in the number of surges, falling behind the Philippines.
SURGEDAT includes just one dot per storm, showing the highest surge for each. For example, Katrina’s dot shows up in Mississippi because that’s where the highest storm surge occurred, though most know Louisiana’s coastline experienced huge surges.
The team is working on developing a way to look at an area’s storm surge history. In a year or two, a person will be able to click on a location along Louisiana’s coastline and see the history of storm surges there even if it wasn’t the highest level, Needham said.
They’re also working on a way to show how often an area gets a certain elevation of storm surge so, for example, a person could look up how many times LaPlace has had a storm surge of 13 feet. They would find that there was more than 13 feet during the 1915 New Orleans storm and during Hurricane Betsy.
“I think a lot of the locals would be surprised to see the 100-year storm is almost 13 feet,” Needham said. “This is a way to bring history back to say there is some vulnerability here.”
Follow Amy Wold on Twitter, @awold10.