May 24, 2013

Hurricane center: Beware of the storm surge

Jennifer Kay / The Associated Press

MIAMI — During a hurricane, the storm surge poses the greatest threat to life and land, yet many people don't even know what it means.

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Residents evacuate their flooded neighborhood in LaPlace, La., in this Aug. 30, 2012, photo, as Hurricane Isaac's winds drove a storm surge into portions of the coast between New Orleans and Baton Rouge.


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Simply put, storm surge is the abnormal rise of sea water. Predicting it is far more complicated and explaining it is tricky, too, as forecasters at the National Hurricane Center discovered, again, during a review of Superstorm Sandy.

This hurricane season, forecasters hope to offer easy-to-understand color-coded maps and they are changing the way they talk to emergency officials, the media and the public.

"Scientists by their very nature use very sophisticated language, technical language," said Jamie Rhome, leader of the hurricane center's storm surge team. "It turns out that nobody else understands what we're talking about. So once we figured that out, we started using more plain language."

Forecasts during Sandy were exceptionally accurate, but often confusing. Perhaps because so many things contribute to storm surge: intensity, pressure, forward speed, size, where it makes landfall and other factors.

Most people believe storm surge is a wall of water, similar to a tsunami, but it's actually just sea water being pushed toward the shore by winds. It can happen quickly and move miles inland, flooding areas not accustomed to being inundated with sea water.

Large death tolls have been blamed on storm surge. At least 1,500 people died during Hurricane Katrina either directly or indirectly because of storm surge, the hurricane center said.

To better explain the danger, forecasters talked to focus groups consisting of local and state officials, law enforcement and hospital associations and other people from Maine to New Orleans. One thing they found out is that when they talk about storm surge, they should say "height" instead of "depth" when explaining how water levels might change.

"We were using 'depth,' thinking this was very clear. It turns out that nobody else does," Rhome said. "They're waiting for height, how high it is, and I would never have guessed in a million years that one word — one word — makes a difference in how people interpret something."

Forecasters also will try to stress that the storm surge isn't just from the ocean and can come from other bodies of water such as sounds, bays and lakes, sometimes well inland.

The hurricane center also plans to show people where to expect storm surge with high resolution, color-coded maps, much like a radar map on the local news showing rain and severe weather. If they can't post the maps on the hurricane center's website this storm season, which begins June 1, the plan is to have the maps ready in 2014.

A National Oceanic and Atmospheric Administration evaluation of the weather service's performance during Sandy also recommended increasing the number of storm surge forecasters at the hurricane center, and providing potential storm surge hazards at least 48 hours before the onset of tropical storm or gale-force winds.

Miami-Dade Emergency Management Director Curt Sommerhoff said his priority is getting the public to understand that the county's evacuation zones are based on storm surge, not hurricane winds.

New data from the hurricane center's storm surge models prompted the county to redraw its storm surge planning zones to include inland areas along canals and rivers that previously weren't identified as being at risk for storm surge.

"That's the new message, the surge danger well inland, well in from the coast," Sommerhoff said.

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