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Hurricane Arthur smashed into the North Carolina coast last week. Just before it hit, residents checked a new storm surge map, found on the National Hurricane Center (NHC) Web Site. It showed them whether they would be above the water driven onto land by the storm or need to evacuate to higher ground. Store owners used it to figure out how high they needed to move their goods off the ground to prevent water damage. Some emergency management crews even utilized it to predict where the hardest hit places could be.
It was the first time the hurricane center has used the experimental tool, called the Potential Storm Surge Flooding Map. It runs potential storm tracks through sophisticated computer models to determine the way water might flow over the landscape when a hurricane hits and produces maps that are color-coded for various danger levels. Storm surges are responsible for a huge amount of damage, injury and death—they are blamed for over half of hurricane-related deaths in the U.S., according to Jamie Rhome, storm surge team lead for the NHC.
In order to help prepare people for potential surges and therefore help reduce injury and death, Rhome took part in the development of this tool, and he says last week showed how well it could work. “We released the maps for Hurricane Arthur a little bit early, prior to the (48-hour) watch/warning phase, just because it was a lot of technology to work through and to make sure everything worked correctly,” he says. “Every map was offered up on time, every advisory was updated in a timely way, which is a huge success.”
The real measure of success, according to North Carolina governor Pat McCrory at a July 4 news conference, was that there were no known deaths or even serious injuries linked to the storm. “That puts a smile on all our faces,” he said. And one of the major reasons for this, according to Rhome, could have been the availability of the storm surge maps. The governor ordered a mandatory evacuation for several parts of the state, including the Outer Banks, where Arthur’s surge was predicted to reach over 1.5 meters in some locations.
The mapping program works by starting with the NHC’s initial forecast of the storm’s most probable track. Then scientists look at the historical errors in that forecast and build alternate scenarios of how the storm may play out. They do repeated runs of the Sea, Lake and Overland Surges from Hurricanes (SLOSH) program, the center’s storm surge model, on each of those scenarios. Rhome says the NHC ends up running SLOSH up to 7,000 times. The result produces several thousand different scenarios. Once those are completed the forecasters then combine the information to create the model, which is used to produce the high-resolution graphic that is offered to the public.
The new mapping system shows different storm surge water levels in varying colors. To ensure that everyone can understand the maps easily, Rhome said all of the features, including the backgrounds, labels and other details, were tested in focus groups. “You are trying to come up with a product that meets everyone’s needs, which is really, really hard,” he says. “We went through this long process of about two years of working with social scientists and communications experts to help us.”
The new tool was not prompted by Superstorm Sandy, which hit the U.S. Northeast in 2012, Rhome said. Rather “it was prompted by earlier storms such as Isabel or Ike, which really helped highlight how hard it is to communicate storm surge,” he says. “You have Ike and Isabel highlighting this…and then you’ve got data that says a majority of the people who die in a hurricane die from drowning. When you put those two together that was kind of the impetus.”
Because the forecast maps are still experimental they will be presented solely on the NHC Web site. This system is going to be refined over the next one or two years, and Rhome says that if it is considered successful, the hurricane center will make it a standard feature and share it more widely. “In the future, if it becomes an operational product, we’d offer up the data and disseminate it through official channels. That’s sort of the next couple of years,” he says.