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When a hurricane approaches, the big threat is storm surge

The Tampa Bay area is one of the most vulnerable places in the United States for hurricane damage. If you wonder why, find a puddle.

Now, kneel next to it and lay your arm on the ground along one side of the puddle. Then sweep your arm across it.

See what happens? The water moves. It sloshes over the banks. It surges out of the puddle and flows over the ants, leaves and twigs that used to sit peacefully along the edges.

Now think of Tampa Bay as a giant puddle and the arm as Arthur, Bertha, Cristobal or some other storm potentially in our future. Swirling storm bands, sweeping in a counter-clockwise motion, could blow the shallow waters of Tampa Bay over their banks.

That would flood people, not ants, and turn their houses into twigs.

"This is the greatest danger that hurricanes pose," said Tom Iovino, communications specialist for Pinellas County.

It happened in Mississippi when Katrina tore through in 2005, wiping entire towns like Waveland off the map.

This flooding is what experts mean when they talk about storm surge, one of the biggest hurricane threats facing the Tampa Bay area, and the reason for the evacuation zones you hear so much about. (You can find maps of your local zones on pages 14-16.)

Storm surge is the water that a hurricane would shove out of the bay or the Gulf of Mexico and into many low-lying areas, such as South Tampa, Oldsmar and portions of St. Petersburg. The evacuation zones are based on the likelihood that saltwater will rise to the level of your home – or over it.

The Tampa Bay area has been lucky: It has not taken a direct hit from a hurricane since 1921. And unlike New Orleans, we don't have whole neighborhoods below sea level that would stay flooded for days.

But if the big one comes – the experts say it's just a matter of time – the peculiar layout of our region will make us particularly susceptible to storm surge damage.

"You have a very large penetration of storm surge from the low ground there," National Hurricane Center Director Bill Read said in an interview. "You have a lot of citizens you have to move in an evacuation."

And, he pointed out, large numbers of elderly people who need extra help evacuating, and a population that's not as used to evacuating people as other places like South Florida that have weathered hurricanes recently.

And if you survived Charley, Frances and Jeanne in 2004, remember none of those were full-force hurricanes when they blew through the Tampa bay area.

To understand the danger, think of the sea floor in the relatively shallow Gulf of Mexico. It slopes up gradually toward shore. When a hurricane comes, it can blow all that water up the smooth, gentle slope, right onto land.

"The bad news is we are as vulnerable as coastal Mississippi was in Katrina to storm surge," said Robert Weisberg, distinguished professor of physical oceanography at the University of South Florida.

On Florida's east coast, it's a slightly different story because the Atlantic drops off more sharply. Without a long and gradual slope beneath the sea, the water doesn't slide up and spill onto land as smoothly, said Wilson Shaffer, chief of the evaluation branch for the National Weather Service.

Pinellas County wanted a way to illustrate the storm surge threat, so it created a 24-foot-high banner and took it to different spots around the county last year. The height of the banner can be adjusted to show how high the waters might rise –- well over 20 feet in some worst-case scenarios.

Even in Pinellas, where people can usually count on a good hurricane scare at least once a year, people were surprised.

"It's stunning," Iovino said. "People will walk up and say, 'I had no idea.' "

It's particularly surprising to see a banner standing six feet high in inland areas such as Pinellas Park. "Even though they can't see the bay or the gulf, it kind of brings home the point that yeah, even here you can get storm surge."

Read, of the National Hurricane Center, said, "The key for your citizens, because of that vulnerability, is to know what their personal threat is as soon as possible."

He urged Tampa Bay residents to learn whether they are in an evacuation zone "and make a personal plan that they enact at the time of the crisis, rather than make up at the time of the crisis."



When a hurricane approaches, the big threat is storm surge 05/15/08 [Last modified: Thursday, May 15, 2008 2:08pm]
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