ST. PETERSBURG, Fla. (AP) — Hurricane Ian made landfall in southwest Florida near Cayo Costa on Wednesday as a catastrophic Category 4 storm.

About 2.5 million people were ordered to evacuate southwest Florida before the storm hit the coast with maximum sustained winds of 150 mph (241 kph). It was heading inland, where it was expected to weaken, at about 9 mph (14 kph), but residents in central Florida could still experience hurricane-force winds.

Before making its way through the Gulf of Mexico to Florida, Hurricane Ian tore into western Cuba as a major hurricane Tuesday, killing two people and bringing down the country's electrical grid.

The center of the massive Category 4 storm lingered offshore for hours, which was likely to mean more rain and damage from a hurricane that was trudging on a track that would have it making landfall north of the heavily populated Fort Myers area. Catastrophic storm surges could push 12 to 18 feet (3.6 to 5.5 meters) of water across more than 250 miles (400 kilometers) of coastline, from Bonita Beach to Englewood, forecasters warned.

"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.

Off the coast on Sanibel Island near Fort Myers, swirling water flooded 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.

"It's going to get a lot worse very quickly," DeSantis said. "So please hunker down."

Fueled by warm waters in the Gulf of Mexico, Ian grew to a Category 4 hurricane overnight with top winds of 155 mph (250 kph), on the threshold of the most dangerous Category 5 status, according to the National Hurricane Center.

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."

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."

Ian made landfall more than 100 miles (160 kilometers) south of Tampa and St. Petersburg, sparing the densely populated Tampa Bay area from its first direct hit by a major hurricane since 1921.

Officials warned residents that Tampa could still experience powerful winds and up to 20 inches (50 centimeters) of rain.

"Please, please, please be aware that we are not out of danger yet," Tampa Mayor Jane Castor said in a video on Twitter. "Flooding is still going to occur."

The most damaging winds could hit a coastline where the population has jumped sevenfold since 1970.

Ash Dugney warily watched ocean water being sucked out below a Tampa Bay pier Wednesday morning. He said he didn't trust Tampa's storm drainage system to keep his corner tuxedo rental business safe from flooding that he said has happened even during mild storms.

"I don't care about the wind and the rain and the stuff like that, I just care about the flooding," Dugney said, adding that he moved essentials out of the shop and moved other items up to above waist-high level.

Flash floods were possible across all of Florida. Hazards include the polluted leftovers of Florida's phosphate fertilizer mining industry, more than 1 billion tons of slightly radioactive waste contained in enormous ponds that could overflow in heavy rains.

Isolated tornadoes spun off the storm well ahead of landfall. One tornado damaged small planes and a hangar at the North Perry Airport, west of Hollywood along the Atlantic coast.

More than 450,000 homes and businesses were without electricity, and Florida Power and Light warned those in Ian's path to brace for days without power.

The federal government sent 300 ambulances with medical teams and was ready to truck in 3.7 million meals and 3.5 million liters of water once the storm passes.

"We'll be there to help you clean up and rebuild, to help Florida get moving again," President Joe Biden said Wednesday. "And we'll be there every step of the way. That's my absolute commitment to the people of the state of Florida."

Parts of Georgia and South Carolina also could see flooding rains and some coastal surge into Saturday. Georgia Gov. Brian Kemp preemptively declared an emergency, ordering 500 National Guard troops onto standby.

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Associated Press contributors include Christina Mesquita in Havana, Cuba; Cody Jackson and Adriana Gomez Licon in Tampa, Florida; Freida Frisaro in Miami; Anthony Izaguirre in Tallahassee, Florida; Mike Schneider in Orlando, Florida; Seth Borenstein and Aamer Madhani in Washington; Bobby Caina Calvan in New York; Andrew Welsh-Huggins in Columbus, Ohio; and Jay Reeves in Birmingham, Alabama.