About the surge: Why Irma caused less flooding than expected

NAPLES, Fla. — Across coastal Florida, the dreaded storm surge from Hurricane Irma — caused when winds pile up ocean water and push it onshore — was not as bad as forecast.

Some areas were hit hard, notably the Florida Keys and Marco Island, but residents of neighborhoods north to Fort Myers, Sarasota and Tampa Bay were expressing relief.

That 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 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.

Irma’s fortunate turn

At the last minute, Irma 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 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 surge was not as strong as feared.

Storm’s center weakens

That weakening was apparent in Fort Myers. When it passed over the city at about 6:15 p.m., the center of the storm, rather than being a well-formed eye, was a jumbled mass of thinner clouds. This suggested the hurricane’s cyclonic structure was coming apart.

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.

When Peter Falisi, his father and 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 flooding. Although there was water in the building, it was not from the ocean: Irma’s winds had peeled off paneling from a roof overhang and broken a water pipe.

Along the southwest Florida coast, only Marco Island, south of Naples, appeared to have suffered from significant flooding. Police officers Monday went door to door on the island, checking on residents who stayed behind. 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.

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 2, shallow enough to only lap at the front steps.

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.

The buffer effect

“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 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 Coral Gables and Palmetto Bay.

As Irma, now a tropical storm, traveled 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.

Still, the damage could have been worse. Chuck Watson, a disaster modeler for Enki Research in Savannah, Ga., had predicted damages as high as $150 billion to $200 billion. But once the storm shifted inland, Watson downgraded those initial estimates to around $50 billion.