More than 7 million people evacuated from the path of Hurricane Irma on Saturday as one the most powerful storms in history lined up a potentially catastrophic strike on Florida.

Slightly weakened after hitting Cuba but still packing an enormously powerful punch, effects of the storm that has claimed more than 20 lives during a week-long 185mph rampage across the Caribbean reached deep into the Sunshine State by late afternoon.

The centre of the category 4 storm was predicted to make landfall in the Florida Keys, the vulnerable low-lying island chain off the state’s southern coast, in the early hours of Sunday. But the outer bands of a storm that Florida governor Rick Scott warned was “wider than the entire state” lashed coastal and inland areas through the day, sparking tornado warnings and widespread loss of power.

At an early evening briefing, Scott said: “If you’re in an area that was told to evacuate, you need to leave now. This is your last chance to make a good decision.”

He added: “Millions of Floridians will see life-threatening winds beginning tonight,” with the “significant threat of serious storm surge along the whole west coast of Florida.”

A storm surge of 15ft would be “devastating and will cover your house”, Scott said. “Do not think the storm is over when the wind slows down. The storm surge will rush in and it could kill you.”

Scott recalled a storm some years ago that brought 6ft storm surges into Naples, on the west coast, and the breathtaking speed of the water that crashed into homes. It was hard to describe, he said, “how fast the water moved in and how fast the water moved out”.

“That was six feet,” he said. “You just think about – how can anybody survive this stuff? I just want everybody to live.”

The projected track of Irma took it up the west coast of Florida during Sunday and in line for a direct hit on the 3 million residents of the Tampa Bay area early on Monday, still as a major hurricane with sustained winds of greater than 140mph. A tornado watch was issued for all of southern Florida.

Radar images of Irma over Cuba’s northern coast showed that the storm’s core had been disrupted by its interaction with land, raising hopes its power could be diminished. But later data showed it regaining shape as it moved back into the warm, open waters of the Florida Straits.

“We’re concerned that as it eases away from Cuba it will strengthen again,” said Max Mayfield, a former director of the National Hurricane Center (NHC). “The core of the hurricane, where the really devastating winds are going to be, is going to move right over the lower Florida Keys early tomorrow morning, and then likely another landfall somewhere on the south-west Florida coast.”

The restrengthening was confirmed by the NHC’s late-afternoon advisory, which forecast a category 4 hurricane at landfall. The agency had earlier adjusted the projected track of Irma’s centre further west, away from Miami, Fort Lauderdale and West Palm Beach in the south east, home to more than 6 million people.

A car drives along an empty highway in Miami, before the arrival of Irma. Photograph: Carlos Barria/Reuters

But NHC specialist Lixion Avila warned that hurricane force winds stretched more than 70 miles from Irma’s centre and that no part of Florida was out of danger.

“There is an imminent danger of life-threatening storm surge flooding in portions of central and southern Florida, including the Florida Keys,” he said. “Irma is expected to bring life-threatening wind and storm surge to the Florida Keys and south-western Florida as an extremely dangerous major hurricane.”

All but deserted from a mandatory evacuation order, the near sea-level Florida Keys island chain was expected to be inundated by up to 15ft of water. Officials reported that the mass evacuation of millions of residents of coastal and vulnerable areas close to inland water had mostly gone smoothly, despite shortages of fuel and gridlock on major highways.

“Very few cars are out there, citizens have taken evacuation warnings very seriously, our shelters are beginning to get full,” said Scott Israel, sheriff of Broward County, where a 4pm curfew was ordered. By late afternoon, however, the northbound I-75 near Ocala was gridlocked.

Further north in Georgia, another half-million residents were told to evacuate. Although Irma is forecast to weaken as it travels north over land, authorities in Georgia and Alabama urged residents to be on alert for heavy rains, wind and flooding as early as Monday.

Across Florida, close to 100,000 customers had lost power by late Saturday, most of them in Miami-Dade and Broward counties. Crews worked to restore about half of them before strengthening winds made it too dangerous to work. The number of outages was expected to grow.

In Miami-Dade county, almost 50,000 were without power. Carlos Gimenez, the mayor, said: “There have been rumours about Miami-Dade being in the clear, being safe. Let me make this clear, Miami-Dade is still being affected by Irma and there are already reports of hurricane force gusts. A serious storm is coming our way and will be here through Sunday.”

In Miami, the streets were virtually empty by Saturday morning, with all petrol stations, supermarkets and other commercial outlets closed. The city was in a state of foreboding, waiting to find out what nature had in store.

In St Petersburg, near Tampa, shelves were bare of essentials – bleach, soup, beans and bread. In one branch of the Publix supermarket, deliveries of ice were announced on a loud speaker with a two-bag maximum per person. Cases of water were also limited to two per person. Every shopper had water. Nearly all had beer.

As the storm approached, people on the western edge of the bay in Pinellas County scrambled to get ready for likely 110mph sustained winds.

“We’ve been having press conferences two or three times a day trying to get people informed, to get them to evacuate,” said Pat Gerard, a county commissioner. “Of course they’re not doing it, but it’s just what they do.”

The last seriously destructive storm to hit Tampa Bay was in 1921, a category 3 hurricane that the National Oceanic and Atmospheric Administration (Noaa) called the “forgotten nightmare”.

Around the county, many said they were making last-minute preparations to for the storm. Putting plywood on windows, charging phones, stocking propane, gas, water and food.

Irma claimed its first fatality in Florida on Friday when a 57-year-old man fell attempting to put up hurricane shutters on a second-story window.

Late on Saturday Donald Trump issued a video of his remarks at a cabinet meeting at Camp David, in Maryland. “This is a storm of enormous destructive power,” the president tweeted. “I ask everyone in the storm’s path to heed ALL instructions from government officials.”

In the morning, Governor Scott said he had “talked to President Trump, he has promised all federal resources [and] I’ve talked to Brock Long, who runs [the Federal Emergency Management Agency], this morning, and he’s guaranteed us all federal resources.

“Florida’s tough, Florida’s resilient and Florida’s unbreakable. This is a great state and we’re going to come out of this very strong.”

 

By Richard Luscombe and Ed Pilkington in Miami, Jessica Glenza in St Petersburg and Alan Yuhas in New York