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Tropical Storm Isaac expected to rebound as hurricane as it moves toward Florida

The Tampa Bay Times Forum, shown on the Garrison Channel, is in evacuation Zone B for category 2 hurricanes. It is the main site of the Republican National Convention beginning Monday. RNC officials said Thursday that they expect the convention to go on.

CHERIE DIEZ | Times

The Tampa Bay Times Forum, shown on the Garrison Channel, is in evacuation Zone B for category 2 hurricanes. It is the main site of the Republican National Convention beginning Monday. RNC officials said Thursday that they expect the convention to go on.

It was only yesterday that Joe Morelli finished righting the palm trees knocked askew by Tropical Storm Debby on Bayshore Boulevard in Tampa.

On the Pinellas beaches, the Pass-a-Grille Marina is still a work zone a month after a tornado spawned by Debby ripped off its roof.

The rivers are swollen, the beaches are eroded and some areas are still water-logged from a combination of Debby and heavy rains this week.

The threat of a strike from Tropical Storm Isaac comes at a time when Tampa Bay is particularly vulnerable to storm surge, flooding and high winds.

"If it hits us, we're definitely worse off than we were before Debby," said Andy Squires, Pinellas County coastal manager.

Forecasters were still uncertain late Thursday night how Isaac would affect Tampa Bay, though the forecasts throughout the day had the storm veering farther to the west — and perhaps away from the bay area.

The storm was about 190 miles southwest of Puerto Rico on Thursday evening, and heading toward Hispaniola and Cuba. Forecasters said it could be a hurricane by today.

If it continues on its current route, Isaac could make a left turn out into the Gulf of Mexico, sparing Tampa from a direct hit while the city is simultaneously welcoming about 50,000 visitors for the Republican National Convention.

But the region is not out of harm's way.

Forecasters on Thursday could not say with certainty what Isaac will look like when it emerges from Hispaniola and Cuba. National Hurricane Center forecaster Jack Beven said the tropical storm could weaken to the point where it would be unable to regroup and gather speed. But if it trains around the islands and sits over warm water, which strengthens hurricanes, it could become a major storm before moving into the gulf.

Compared to Debby, which had tropical storm winds extending 200 miles from its center, Isaac's winds reach 185 miles out. And with an average speed of 18 mph, it is traveling faster than its predecessor, which parked over the bay area for days before moving on.

Isaac could be bad news for coastal areas prone to the effects of storm surge, experts said. Surge is difficult to predict as it depends largely on rapidly changing factors such as a storm's size, speed, reach and intensity. Beven noted "significant uncertainty" remains about Isaac's ability to harm Florida.

Emergency management officials in Hillsborough and Pinellas said it was too soon to predict whether the storm surge and rainfall would flood neighborhoods and force evacuations or bypass the Gulf Coast of Florida on its way north.

"The models are all over the place right now, and we're not going to declare a state of emergency until we've got a higher probability of the storm coming here," said Pinellas County spokesman Tom Iovino.

Declaring a state of emergency would propel the county's storm-response systems into action and give them the authority to call for evacuations, a step they would take in low-lying areas that are likely to flood or in regions that, though dry, could easily be cut off from major roads and bridges by rising water levels. Both counties have five evacuation levels — lettered A through E — that depend on the severity of the storm. Because of mobile home parks' susceptibility to high winds, their residents are required to leave regardless of the likelihood of flooding.

When the "preponderence of data" tips toward major flooding, county officials make the call, Iovino said. There is no set threshold.

Hillsborough County Sheriff David Gee dismissed the possibility of damage from storm surge, noting that Pinellas, with its barrier islands in the gulf, is more likely to get swamped.

But if Isaac were to approach the bay area from the southwest, high winds would move mass amounts of water into Tampa Bay, causing tremendous flooding, particularly in Hillsborough County, where the Interbay Peninsula could be virtually under water.

Most forecasters do not think Isaac will come from this angle, but they noted that its projected route would bring it parallel to the peninsula and could create threatening waves and flooding.

The bay area's rivers and lakes are already elevated after several days of heavy rainfall, and in Hillsborough, officials issued flood warnings for three rivers: Little Manatee in Wimauma, Alafia River in Lithia and Cypress Creek in Worthington Gardens. The Hillsborough River is also rising, they said.

In Pinellas County, this week's rains overwhelmed a water treatment plant, prompting officials to urge residents to cut back on flushing toilets, washing clothes and bathing.

Many of Pinellas County's beaches, which lost more sand to Tropical Storm Debby than any other storm in the past decade, still look bruised, their dunes eviscerated and hundreds of thousands of cubic yards of expensive sand lost to offshore sandbars. As natural barriers shielding homes and businesses from damage, the dunes are not in fighting condition.

"South of Sand Key, Pinellas beaches are pretty sad," said Squires, the Pinellas coastal manager.

Last week, he delivered 4,000 sea oat seedlings to Sand Key beach, where contractors have been dredging sand miles offshore and pumping it back onto the beach. Planted in hopes that they would eventually rebuild sand dunes, the oats could easily be washed out to sea in a storm.

University of South Florida geology professor Ping Wang predicted that a stronger and faster storm like Isaac would bring higher waves and more dune erosion than Debby. The sandbars will slow down the water somewhat, he said, but are likely too small to prevent a storm surge from rising over them and past seawalls, dunes, and roadways.

Morelli, who is responsible for the 42 Florida date palms that line Bayshore Boulevard, said he hoped they would withstand another storm.

"As long as the water recedes quickly, they should be fine," he said. "It's that brutal wind that just tears things up."

Times staff writer Jessica Vander Velde contributed to this report.

Tropical Storm Isaac expected to rebound as hurricane as it moves toward Florida 08/23/12 [Last modified: Friday, August 24, 2012 1:55am]

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