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2014 Hurricane Preparedness Week – Day 2

Storm Surge

 

 

[via Claire Taylor, The Advertiser ]

When a hurricane forms, the National Hurricane Center uses computer models to forecast its potential path and landfall, and assigns it a category number based on the strength of its winds.

Left out of the equation is the potential risk of storm surge flooding, which doesn’t necessarily correlate with the wind speed.

That’s changing this hurricane season. With each storm, the National Hurricane Center will generate interactive maps residents can use to predict how much storm surge flooding their communities might see.

“One of the biggest misnomers was people would try to correlate a Category 4 storm with a certain amount of storm surge,” said James Brinkley, storm surge operations manager with the National Hurricane Center in Miami.

Hurricane Charley was a Category 4 hurricane when it struck western Florida in 2004, carrying an 8-foot surge, Brinkley said. Hurricane Ike in 2008 was only a Category 2 hurricane, but it generated a 16-foot surge that flooded much of the Louisiana and Texas coast.

Here’s how storm surge works: A hurricane’s winds pushes the ocean water toward the coast. When the surge arrives at the same time as the incoming tide, the water piles even higher.

Many variables contribute to the size of a storm surge, including the forward speed and direction of the storm, the shape of the coastline, the underwater topography, the size of the storm, and the presence of rivers, bays and inlets, he said.

“Surge in Louisiana is not the same as surge in Florida or in the Northeast,” said Jonathan Brazzell, a hydrologist with NOAA and the National Weather Service in Lake Charles. “There are totally different land forms and topography.”

Some areas along the Gulf Coast, especially Louisiana and Mississippi, are particularly vulnerable to storm surge because the ocean floor gradually deepens offshore.

The new storm surge maps will be generated when a hurricane watch or warning is issued, typically 48 hours before the onset of tropical storm-force winds, Brinkley said. The maps will be updated every six hours in conjunction with the hurricane center’s advisory packages because small variations in wind and direction can cause significant changes to storm surge, he said.

The interactive maps will use different colors indicating varying depths of water to help residents prepare for the storm surge, Brazzell said.

“You can zoom in and find your community — not your specific house — and determine how much threat you can expect” from storm surge, Brinkley said.

“That’s a plausible worst-case scenario,” Brazzell said. “There’s still a 10 percent chance that value will be exceeded.”

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