If path holds, Irma could swamp Southwest Florida, Tampa coast with surge

As the projected path of Hurricane Irma shifts to Southwest Florida, it threatens to hit the nation’s most vulnerable target for storm surge: Tampa.

Tampa is especially prone to flooding because it is low lying with a big bay and inlets that face the shallow, warm waters of the Gulf of Mexico. And just every Gulf Coast community in Irma’s track, from Everglades City to Sarasota, is also at high risk.

Tampa leaders are all too aware of this scary natural phenomenon.

“Storm surge is real. I think it’s ‘You run from the water and hide from the wind.’ ’’ Hillsborough County Commissioner Sandy Murman said, urging residents to take all precautions at an emergency briefing on Saturday.

“Well, you better run from this water because if that storm surge hits six to nine feet, I know I’m going to have six feet in my house.”

Tampa — Florida’s second largest metro area — has been rated as the nation’s most vulnerable city to a major storm with estimated property losses of $175 billion in the event of a 100-year hurricane, according to a Boston company that specializes in assessing the risk of catastrophes.

In Tampa, the 100-year hurricane would be a Category 4 storm with winds as high as 150 miles per hour. Irma, whose peak winds were clocked at 125 miles per hour on Saturday, is a Category 3.

“A severe storm with the right-track orientation will cause an enormous buildup of water that will become trapped in the bay and inundate large areas of Tampa and St. Petersburg,” with 50 percent of their population living on ground elevations less than 10 feet, according to a 2015 report by Karen Clark & Company.

The company rated Fort Myers No. 5 in vulnerability with estimated losses of $70 billion, and Sarasota at No. 7 with losses estimated at $50 billion.

By comparison, Miami came in at No. 4 with estimated losses at $80 billion. Miami’s coastal profile is less prone to storm surge than other areas because the continental shelf falls off steeply, the report said. But its potential property losses are still high because the city boasts some of Florida’s most expensive real estate.

Irma, which earlier in the week was projected to strike South Florida, started shifting to a northwest track on Friday toward Southwest Florida. Typically, in this region, storms travel east to west or southwest to northeast — as Hurricane Charley did in 2004, when the Category 4 storm made landfall west of Fort Myers.

However, Irma’s path appears to be heading parallel to the Southwest coast from Naples to Tampa — and that would cause the Gulf’s shallow bays to bulge. The storm surge — the difference between normal high tide and storm tide — is predicted to range from six to nine feet depending on the coastal area, the National Hurricane Center forecast.

If Irma’s eye wall cuts across the Tampa-St. Petersburg metro area, it would not only bring destructive winds to the densely populated cities but could also fuel a catastrophic storm surge into Tampa Bay, according to a worst-case scenario by The Weather Channel.

When Hurricane Charley threatened the same area in 2004, an oceanographer at the University of South Florida’s marine college said that highlighted an example that would cause widespread inland flooding.

“The worst case is if the storm parallels the coast and comes ashore north of the bay,” USF professor Robert Weisberg told the Miami Herald in August 2004, before Charley would ultimately make landfall 90 miles south of Tampa.

Weisberg explained that if Charley struck that end, its back side would drive storm surge well inland because the shallowness of the Gulf and Tampa Bay leaves no other place for the water to go.

Two things increase the Tampa area’s vulnerability, said then-National Hurricane Center oceanographer Stephen Baig: Its low-lying coast and shallow surrounding waters. Even 25 miles off the coast, the Gulf of Mexico is only about 60 feet deep.

“The west Florida shelf is very broad,” Baig told the Herald. “That’s extremely conducive” to storm surge. In essence, water driven by a hurricane has no place to go but up — very quickly.

“Most people have no idea how fast water can rise up because most of us have never seen a 100-mile-an-hour wind lift up water,” Baig told the Herald in 2004.

Scientists and forecasters stress that surge impacts can vary widely depending on the intensity, speed, angle and landfall of a storm.

But one thing is clear: storm surge is deadly serious. The National Oceanic and Atmospheric Administration has identified storm surge as the most damaging aspect of a hurricane, because it destroys buildings and drowns people.