The monster surge that wasn’t: Why Hurricane Irma caused less flooding in Florida than expected

Floodwaters below Interstate 95 in Jacksonville, Florida, on Monday.

NAPLES, Fla. — Across coastal Florida, the dreaded storm surge from Hurricane Irma — caused when ferocious winds pile up ocean water and push it onshore — was not as bad as forecast. While some areas were hard hit, notably the Florida Keys and Marco Island, residents of neighborhoods north to Fort Myers, Sarasota and Tampa Bay were expressing relief.

That bit of good fortune was the product of some meteorological luck.

Because a hurricane’s winds blow counterclockwise, the precise path of the storm matters greatly for determining storm surge. Had Irma lingered far enough off Florida’s Gulf Coast, its eastern wall, where the strongest winds occur, could have shoved 6 to 9 feet of water into parts of Fort Myers and Naples, while swamping Tampa Bay and St. Petersburg as well.

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At the last minute, Irma unexpectedly veered inland right before it got to Naples, taking its eastern wall safely away from the ocean. That meant that as the storm tracked north over Naples, Fort Myers and Tampa Bay, the winds at the head of the storm were moving west and actually pulling water away from the shoreline. In Tampa, water levels dropped 5 feet below normal, and bewildered spectators walked out to see beaches sucked dry. In Sarasota, a manatee became stranded.

Then, once the eye of the hurricane had passed through those areas, the back side of the storm hit, pulling water east toward the coast. But by this point, the storm’s winds were weakening, and the resulting surge was not nearly as strong as feared.

That weakening was readily apparent in Fort Myers. When it passed over the city at about 7:15 p.m. Eastern time, the center of the storm, rather than being a well-formed eye, was a jumbled mass of thinner clouds. This suggested that the hurricane’s cyclonic structure was beginning to come apart.

Hurricane damage on Marco Island, Florida, on Monday. Though the island and the Florida Keys were hard hit, the state was largely spared a devastating storm surge.

Some parts of Fort Myers and Naples saw sea levels surge 4 to 5 feet above normal levels — a damaging flood, but less than early warnings had suggested.

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When Peter Falisi, his father and other family members went to check on the restaurant they were renovating Monday, they weren’t sure what they would find.

The neighborhood, near the Naples airport, had been forecast to get a storm surge of up to 6 feet above ground. That would potentially cause catastrophic flooding at the business, Two Guys Kitchen and Catering, which they hoped to open in a month.

When they arrived, there was little sign of any flooding. Although there was some water in the building, it was not from the surging ocean: Irma’s winds had peeled off paneling from a roof overhang and broken a water pipe.

“The only water we have inside is from the broken sprinkler system,” Falisi said.

Along the Southwest Florida coast, only Marco Island, south of Naples, appeared to have suffered from significant flooding. Police officers on Monday went door to door on the island, checking on residents who stayed behind to ride out the storm. No deaths or serious injuries were reported.

In Fort Myers early Monday morning, there were few signs of flood damage. Across the Caloosahatchee River in North Fort Myers, residents returned to mobile home parks to find them dry and intact, with what damage there was coming largely from wind, not water.

Trying to keep the water out at a hotel in Miami on Sunday.

And in East Naples neighborhoods, where inundation maps suggested as much as 9 feet of water, at most homes there was little more than a foot or two, shallow enough to only lap at the front steps.

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Tampa and St. Petersburg saw just 2-3 feet of storm surge, according to data from Hal Needham, a storm surge expert and founder of the private firm Marine Weather & Climate.

“That initial draining of water acted as a crucial buffer,” said Rick Luettich, director of the University of North Carolina’s Institute of Marine Sciences and an expert on storm surge. “By the time the back side of Irma hit, the storm was further inland and not quite as strong.”

Yet because Irma was so unusually large, its fierce winds also extended all the way to the east coast of Florida, pushing water inland there. Needham estimated that salt water levels rose 4 feet above normal in Miami — the 10th highest level seen since 1880.

That produced a river of water pouring into downtown Miami and Brickell, the city’s financial district. Water rose several feet up the stairs of buildings and storefronts, and at one point, whitecaps dotted the makeshift river.

The surge also caused flooding in the enclaves of Coral Gables and Palmetto Bay.

As Irma, now a tropical storm, traveled further north Monday, its eastern winds continued to push water up into the coasts of eastern Florida and Georgia, with parts of the region facing 7 feet of storm surge. In Jacksonville, coastal surges and heavy rains have swamped the central business district and swelled the nearby St. Johns River.

Sea-level rise caused by climate change also worsened the storm surge that did occur in many areas. In Miami, sea levels have risen roughly 10 to 12 inches in the past century. “That may not sound like a big deal, but when combined with a 4 foot surge, it can mean the inundation of thousands of more buildings,” said Needham.

Still, the damage could have been far worse. Chuck Watson, a disaster modeler for Enki Research in Savannah, Georgia, had initially predicted total damages as high as $150 billion to $200 billion, which would have made Irma the costliest storm in U.S. history.

But once the storm shifted inland, Watson downgraded those initial estimates to around $50 billion, which would still make Irma one of the five costliest hurricanes on record in the country. While high winds and heavy rainfall were still expected to cause major damage to buildings, the reduced storm surge made a big difference.

“There’s always a lot of uncertainty with storms that run south to north,” said Watson. “If the storm shifts just 50 miles east or west, that can make a huge difference in terms of damage.”

Experts also warn that Florida’s west coast should not get too complacent after this bout of relative good fortune. If a major hurricane were to travel from the Gulf of Mexico and barrel northeast directly into Tampa Bay, that could produce surges of 15 feet or more.

“The west coast of Florida still has plenty of disasters that are waiting to happen,” said Luettich. “This was really a best-case scenario, from a track perspective, for a storm this strong.”

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Lizette Alvarez contributed reporting from Miami and Christine Hauser from Marco Island.