There’s little to feel good about a monster Category 5 hurricane bearing down on South Florida. But there is this:
Irma shouldn’t be anywhere near as wet as Harvey.
Harvey hunkered down over the Texas coast for more than four days, dumping upwards of 50 inches of rain, turning interstates into rivers and drowning homes up to the rooflines. Irma will bring heavy rain, but its biggest threat is its fearsome wind — the sustained winds were still clocking at 175 mph late Thursday, with high gusts. The sort of power wrapped in Irma’s eye can rip off rooms and knock down walls.
Forecasters and emergency managers worry about a swath of catastrophic wind field damage somewhere in South Florida — although there is still a chance Irma could wobble off shore and spare South Florida’s densely populated coastline a direct hit.
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Along the coast and in some vulnerable areas inland, such as along the Coral Gables Waterway, there could be impacts from rising water levels — but in the form of storm surge as Irma’s approach pushes the Atlantic Ocean onto land.
When it makes landfall, the National Hurricane Center predicts Irma will bring between 5 and 10 feet of storm surge along the southeast coast, with a storm surge warning stretching from the Keys up to West Palm Beach. The warning also affects inland areas, like Coral Gables, which are potentially vulnerable because of its canal system.
“If extreme force is pressed upon the ocean, it will snake its way inland however it can,” said Jamie Rhome, NHC’s storm surge expert.
That estimate could change depending on when Irma makes landfall. If the storm hits during high tide, more water will slosh inland. But it’s too soon to say what the tide will be when Irma comes ashore. Historically, coastal storm surge is the deadliest impact from hurricanes — and the predicted surge from Irma to some islands in the Turks and Caicos is up to 20 feet, a rise that could easily flood communities there.
Andrew Hagen, a meteorologist with the National Weather Service, said the six-hour window between low and high tide means the slow-moving storm will likely hit some part of Florida’s east coast at high tide.
“We probably won’t really know that until 24 hours before landfall,” he said.
Forecasters expect Irma to bring 8 to 10 inches of rain across much of South Florida, with some areas in the north Keys seeing closer to 15 inches. In a region where a summer thunderstorm can flood cars in low-lying areas or poorly draining parking lots, that could cause some problems — serious in some areas. But the rain isn’t expected to turn neighborhoods into lakes.
If Irma crosses near Lake Okeechobee, Florida’s biggest body of water, it also could add stress to the aging and vulnerable Herbert Hoover dike. But state and federal leaders said they were confident about the integrity of the dike, which has undergone millions in repairs since it was heavily damaged by hurricanes in 2004 and 2005.
The state “does not have major concerns” about the dike’s stability, Gov. Rick Scott said Thursday, but “we will immediately advise if that changes.”
Although scientists are comparing Irma to Hurricane Harvey in terms of severity, Dennis Feltgen, spokesman for the National Hurricane Center, said there are clear differences between the storms. Unlike Harvey, a slow moving storm that sat on Houston for days dumping more than 50 inches of rain, Irma is likely to move across the area faster.
“When we forecast Harvey as a catastrophic storm, that was because you could measure the rainfall in feet,” Feltgen said. “Now with Irma, it’s forecast as catastrophic because of the wind.”