Irma's weird wallop

Photo: The Canadian Press

Hurricane Irma's devastating storm surge came with weird twists that scientists attribute to the storm's girth, path and some geographic quirks.

A combination of storm surge, heavy rains and swollen rivers sent some of the worst flooding into Jacksonville, Florida, even though Irma roared into the opposite end of the state, had weakened to a tropical storm and its eye stayed at least 130 kilometres away.

Although preliminary data suggest Irma's eye pushed a surge of more than 3 metres onto southwest Florida's Marco Island, the highest water levels were reported hundreds of miles away in Jacksonville and Savannah, Georgia, according to the National Oceanic and Atmospheric Administration.

And southwestern Florida, which is prone to surges, saw the opposite at first: a strange-looking negative surge that sucked the water off the sea floor quickly enough to maroon several manatees. After the water pulled away from the beaches and bay, it came back with vengeance, but much of Florida's west coast wasn't swamped as badly as it could have been because Irma's track kept them safe from the storm's stronger eastern side.

"You can call it bizarre; I might call it unusual or unique," said Rick Luettich, director of the Institute of Marine Studies at the University of North Carolina. "What was very unusual about it was, it spanned two coastlines that were in different-facing directions. As a result, you got the opposite behaviour on both coastlines."

Tampa "dodged a bullet" on the weaker side of the storm, especially because Irma's southwestern eyewall had been broken up by high winds near Cuba, MIT meteorology professor Kerry Emanuel said.

Jacksonville and the rest of the east coast, on the other hand, got the northeast brunt of the storm, where winds, surge and rainfall are at the strongest. And because hurricane winds spin counterclockwise and lined up perfectly perpendicular to Jacksonville's St. Johns River, "it just pushed the water from the Atlantic right into the river," National Hurricane Center spokesman and meteorologist Dennis Feltgen said.

The city's concave coastline and the shallow water off the beach also made for a bigger storm surge buildup, funneling more water into Jacksonville, said storm surge expert Hal Needham of Galveston, Texas.

On top of that, Jacksonville — unlike western Florida — only got one side of Irma, so the wind kept coming from the same direction, pushing the surge even higher, Needham said.

That's why Paul Johnson was surprised when Monday morning he woke up in Jacksonville, looked out the window and saw boats passing by where cars normally drive. The water was lapping at his front door. Before long, the flooding rose nearly to the window of his beloved pickup truck.

"I've lived here most of my life, and I've never seen anything like that," he said.