Hurricane Irma strengthened to a Category 4 storm overnight and was expected to move over the lower Florida Keys early Sunday before heading toward the southwest coast later in the day, the National Hurricane Center said at its 5 a.m. briefing.
Sustained winds are near 130 mph, with higher gusts.
Tropical storm conditions are expected Sunday in the Bradenton area, with hurricane conditions expected Sunday night, according to the National Weather Service office in Tampa.
Winds will steadily increase throughout the day. About 5 inches of rain is forecast to fall between 2 and 8 p.m., with another 3 inches possible between 8 p.m. and 2 a.m., according to the latest hourly forecast.
Sustained winds of 100 mph or more could arrive by around 11 p.m. Sunday, with gusts near 125 mph.
Along the Gulf Coast, forecasters warned that flooding from storm surge could be catastrophic, with water rising as high as 15 feet from Cape Sable to Captiva. The storm surge from Ana Maria Island to Clearwater Beach, including Tampa Bay, could be as high as 8 feet, the NHC said.
“This is a big hurricane,” said Jamie Rhome, NHC storm surge team leader. “And big hurricanes push more water.”
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 pass 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.
Jenny Staletovich and Charles Rabin of the Miami Herald contributed to this report.