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Saturday, Oct 21, 2017
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Bermuda high system is bringing Hurricane Irma Tampa Bay's way

Blame the Bermuda high.

Tampa Bay residents troubled by a westerly shift in Irma's forecast track can point their fingers at the huge area of high pressure that usually hovers over Bermuda.

For days, forecasters have been calling for the storm to make a drastic northerly turn. But when? For Tampa Bay, the answer could mean the difference between tropical storm and hurricane force winds.

Earlier in the week, the track showed Irma making landfall near Miami and tracking along or just off the state's east coast. Now, models are coalescing around a forecast track that shows Irma turning later, making landfall closer to Naples, and the Bermuda high is why, said Stephen Shively, a forecaster for the National Weather Service in Ruskin.

"We thought it might scoot away from Irma, but it didn't," Shively said.

Counterclockwise winds around the Bermuda high steer tropical systems, so the position of the high is a big factor in whether storms curve harmlessly out to sea or continue west, threatening the Caribbean and United States. The placement of the high is what pushed Irma to the south, along a westerly track.

Meanwhile, an area of low pressure has been moving from over the western United States into the Gulf of Mexico. Irma is going to be squeezed between the low and high, forcing that drastic northerly turn, Shively said.

If the high had weakened and scooted east, Irma would have made the turn sooner. Instead, the opposite happened.

"The high got stronger and stayed in place," Shively said.

Though confidence in the forecast track has increased, there is still a margin of error that could translate to a big difference in Tampa Bay.

The current track shows the center of Irma traveling up the spine of the state through Polk County. If it shifts 15 miles to the west, "It would be in Hillsborugh County," Shively said.

Hurricane force winds extended about 70 miles from the center of the storm, so that could mean sustained tropical force winds of about 65 miles per hour in the Tampa Bay area when the storm rolls through late Sunday and into Monday, Shively said.

Wind gusts could reach Category 2 strength, up to about 100 mph, forecasters say.

"And 30 miles to the east would make Tampa Bay quieter," he said.

While we're blaming the Bermuda high, though, we should also be grateful it hasn't shifted farther west.

That would have meant a "worst-case scenario" for Tampa Bay, with the storm remaining just off shore, maintaining or even gathering strength as it buzz-sawed up the Gulf Coast with potentially catastrophic rainfall and storm surge.

Weather Center

10Weather WTSP

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