Cat 3 Irma moving into Florida Straits, should intensify before striking Keys

Hurricane Irma could regain the intensity it lost near Cuba as the storm moves across the Florida Straits tonight, headed toward the Lower Keys pushing huge waves and a storm surge that could flood some low-lying islands.

In a 5 p.m. advisory, National Hurricane Center forecasters said Irma had begun moving away from the Cuban coast, where it had lingered for most of the day and weakened slightly. The storm was located 115 miles southeast of Key West, with sustained winds of 125 mph, but still holding onto major Category 3 strength. Once it begins crossing warm water, it could strengthen to 140 mph in the 24 hours before it reaches the Keys. At daybreak Sunday, Irma could bring life-threatening and catastrophic conditions to a string of islands, they said.

"We expect it to re-intensify," said hurricane specialist Mike Brennan. "If you've been asked to evacuate, please evacuate."

While the forecast track shows the storm’s center crossing south of Big Pine, fierce winds and storm surge will likely be widespread since hurricane-force winds stretch 70 miles from Irma’s center. A long-expected turn to the northwest has also begun, said acting director Ed Rappaport.

Waters should begin rising between 8 p.m. and 2 a.m. tonight along the eastern side of the islands and from 8 a.m. to 2 p.m. on the west side, Brennan said. The surge could go as high as 10 feet throughout the Keys. From Card Sound Road to Miami Beach, a four to six-foot surge is possible, he said.

Along the Gulf Coast, forecasters warned flooding from storm surge could go higher and be catastrophic, with water rising as high as 15 feet from Cape Sable to Captiva.

"This is a big hurricane," said Jamie Rhome, NHC storm surge team leader. "And big hurricanes push more water."

In 1998, Hurricane Georges, a smaller less intense storm crossed near Cudjoe and delivered a 10 to 12-foot storm surge, cuting off water and electricity to the lower islands and leaving the Lower Keys a ragged mess.

On Saturday, tropical storm force winds started lashing parts of the Florida chain of islands, pushing storm surge ashore. Water levels were up throughout the day, rising nearly a foot above normal in Key West after 4:30 p.m. and more than a foot near Vaca Key. The center of the storm is not expected to pass until Sunday morning, before heading to Florida’s Gulf Coast. Winds well in excess of 100 mph are expected but the real worry is storm surge, which could push the Atlantic into the streets of Key West, Marathon and other islands.

Where Irma ultimately makes landfall on the mainland remains uncertain because of the storm’s angle to the coast, forecasters said. The storm’s center could near Tampa Bay, which has not been struck by a major hurricane since October 1921, when the population was about 10,000, said hurricane center spokesman Dennis Feltgen. About 4 million people now live in the low-lying area.

“Big difference,” he said. “They’re incredibly vulnerable.”

On the current forecast track, Irma’s center crosses the Keys east of key West, where Hurricane Georges hit in 1998 and delivered a 10 to 12-foot storm surge, cutting off water and electricity to the islands and leaving the Lower Keys a ragged mess. Hurricane and storm surge advisories have been widened in Florida and up the U.S. east coast.

The Keys should brace for a “very life-threatening event,” Brennan said, with storm surge capable of reaching 10 feet above ground level.

Miami and the southeast coast have dodged a direct hit, but the east coast can still expect dangerous storm surge as strong winds push water inland and feeder bands drop heavy rain. By 4 p.m., sustained winds nearly reached 53 mph at the Fowey Rocks Lighthouse in Biscayne Bay. Storm surge had pushed water levels 1.27 feet above normal with a gust nearing 50 mph at Viriginia Key.

At 390 miles wide, Irma is considered a moderate to large storm, Rappaport said. That makes it smaller than Katrina and Wilma, he said.

A tornado watch has also been issued until midnight across the state, from Lake Okeechobee south to 40 miles east of Marathon, the National Weather Service said. Wind gusts could also reach 70 mph, they said.

Long periods of thunderstorms should begin tonight as conditions worsen, said Mark DeMaria, the NHC’s acting deputy director.

"This is a major storm surge threat, a major wind threat for a large portion of Southwest Florida," he said.

The storm is expected to batter Florida for at least two days, Brennan said. The latest forecast track also crosses dangerously close to Captiva and Sanibel in an eerie repeat of Charley. But hurricane wobbles are notorious. Forecast tracks can still be off by about 90 miles at two days, Brennan said.

Along Florida’s Gulf Coast, flooding is expected to be widespread, with dangerous and potentially catastrophic storm surge rolling up and down the Florida coast.

Above-ground water levels could reach up to 10 feet along the east coast from Cape Sable to Boca Raton, forecasters said. On the Gulf coast, where the flat continental shelf worsens the threat, the surge could reach 15 feet from the cape to Captiva. Flood-prone Tampa could see three to five feet.

Heavy rain could worsen flooding. Up to 20 inches are possible in the Keys, with up to 25 inches in some places. The Florida mainland is expected to get between eight and 15 inches.

This story was originally published September 9, 2017 at 5:14 PM with the headline "Cat 3 Irma moving into Florida Straits, should intensify before striking Keys."