Beginning in 2015, the National Hurricane Center will make it easier for coastal communities to determine what their storm surge risk is from an approaching hurricane.
Improvements in storm surge modeling are enabling the National Hurricane Center to offer better surge forecasts. The center will begin to issue separate watches and warnings for storm surge along the U.S. coast, in addition to the current watches and warnings for hurricane and tropical storm winds. The new products will start to grace the center’s website during the 2015 hurricane season and be phased into full production by 2017.
“Hurricane warnings have covered both the wind and water hazards,” says Jamie Rhome, the center’s storm surge lead. “But, one can arrive before the other and the threat levels can be different. It’s hard to communicate the total threat.”
Rhome says that while forecasters know where surge is most likely and how deep it will be in different places, passing this information on to the public has been difficult. “Storm surge has kind of been getting lost in the message for wind,” he said.
The new watch and warning maps will compliment the center’s experimental potential storm surge flooding map, which they began using in 2014. These maps show where surge flooding is expected as well as a forecast for depth of the water above ground level.
Many people, including those that do not reside in hurricane-prone areas, are familiar with the Saffir-Simpson hurricane categories. “Everybody seems to know that a category 5 is worse than a category 2,” Rhome says. However, since the hurricane categories are based only on wind speed, they are not always a good measure of a storm’s potential storm surge flooding.
A hurricane’s surge — or ocean water inundation onto land — is the product of a number of variables, including the storm’s wind speed and direction, minimum central pressure, and the shape of the shoreline and ocean floor right off the coast. All of these factors come together to create a unique storm surge in every hurricane landfall.
And historically, storm surge has been the biggest tropical cyclone killer around the world.
“Hide from the wind, run from the water,” tends to be the motto forf hurricane safety. That is, if you are absolutely sure that the building you’re in will withstand a storm’s fastest winds, and that the location is far enough away from the water to be safe from storm surge, you’re probably okay to shelter there. But, if you have any doubts about the building’s strength or there is any chance of surge filling the building with water or washing it away, you should evacuate.
The storm surge forecast issued around the time of your evacuation deadline might only put the risk of a major surge at 10 percent, for example. But in the time it takes for the hurricane to arrive, the storm could strengthen and the forecast could change, leaving you with few options. And many emergency managers and officials would argue that a 10 percent storm surge risk is not actually as low as it seems.
Which is why emergency managers need surge forecasts as far ahead of a storm’s arrival as possible, and will order — or strongly suggest — evacuations when the forecast risk is seemingly low for surge flooding.
However, don’t expect any new hurricane categorization based on storm surge. “We already have a scale for surge, it’s called ‘feet,'” said Rhome. “If I tell you the surge could be six feet at your house and you’re five-and-a-half feet tall, you get the picture.”