Live Video Coverage of Ian: After slamming Ft. Myers and the south Suncoast he keeps rolling through the state.

ST. PETERSBURG, Fla., (AP) — Hurricane Ian’s most damaging winds began hitting Florida’s southwest coast Wednesday, lashing the state with heavy rain and pushing a devastating storm surge after strengthening to the threshold of the most dangerous Category 5 status.

Fueled by warm waters in the Gulf of Mexico, Ian grew to a catastrophic Category 4 hurricane overnight with top winds of 155 mph (250 kph), according to the National Hurricane Center. The storm trudged on a track that would have it making landfall north of the heavily populated Fort Myers area, which forecasters said could be inundated by a storm surge of up to 18 feet (5.5 meters).

“This is going to be a nasty nasty day, two days,” Florida Gov. Ron DeSantis said, stressing that people in Ian’s path along the coast should rush to the safest possible shelter and stay there.

Ian menaced Florida after bringing destruction Tuesday to western Cuba, where two people were reported dead and the storm brought down the country’s electrical grid.

Ian’s center was about 25 miles (40 kilometers) west of Fort Myers at 2 p.m. Wednesday, as it churned toward toward the coast at 9 mph (15 kph). The storm was expected to spend a day or more crawling across the Florida peninsula, dumping flooding rains of 12 to 18 inches (30 to 45 centimeters) across a broad area, including Tampa, Orlando and Jacksonville.

Catastrophic storm surges could push 12 feet (3.6 meters) of water or more across more than 250 miles (400 kilometers) of coastline, from Bonita Beach to Englewood, the hurricane center warned.

“It’s going to get a lot worse very quickly. So please hunker down,” DeSantis said.

Off the coast on Sanibel Island near Fort Myers, swirling water covered residential streets and was halfway up mailbox posts by mid-morning. Seawater rushed out of Tampa Bay, leaving parts of the muddy bottom exposed, and waves crashed over the end of a wooden pier at Naples.

Ian’s rapid strengthening prompted Fort Myers handyman Tom Hawver to abandon his plan to weather the hurricane at home and head across the state to Fort Lauderdale.

“We were going to stay and then just decided when we got up, and they said 155 mph winds,” Hawver said. “We don’t have a generator. I just don’t see the advantage of sitting there in the dark, in a hot house, watching water come in your house.”

More than 2.5 million people were under mandatory evacuation orders, but by law no one could be forced to flee. The governor said the state has 30,000 linemen, urban search and rescue teams, and 7,000 National Guard troops from Florida and elsewhere ready to help once the weather clears.

Florida residents rushed ahead of the impact to board up their homes, stash precious belongings on upper floors and join long lines of cars leaving the shore.

Some chose to stay and ride out the storm. Jared Lewis, a Tampa delivery driver, said his home has withstood hurricanes in the past, though not as powerful as Ian.

“It is kind of scary, makes you a bit anxious,” Lewis said. “After the last year of not having any, now you go to a Category 4 or 5. We are more used to the 2s and 3s.”