MIAMI (AP) -- Hurricane Irma is done with Cuba and is slowly chugging to the Florida Keys and the state's west coast.
The National Hurricane Center extended storm surge and hurricane warnings on both sides of Florida's coasts.
The center warns the threat of catastrophic storm surge flooding is highest along the southwest coast of
Florida, where 10 to 15 feet of inundation above ground level is expected.
Southwest Florida is sometimes called "surge central" by storm experts.
With the window closing fast for anyone wanting to escape, Irma hurtled toward Florida with 125 mph winds Saturday on a shifting track that took it away from Miami and instead threatened the Tampa area with its first direct hit from a major hurricane in nearly a century.
"You need to leave - not tonight, not in an hour, right now," Gov. Rick Scott warned residents in the evacuation zones ahead of the storm's predicted arrival on Sunday morning.
For days, the forecast had made it look as if the Miami metropolitan area of 6 million people could get hit head-on with the catastrophic and long-dreaded Big One.
The swing in the hurricane's projected path overnight caught many on Florida's Gulf coast off guard. By late morning, few businesses in St. Petersburg had even put plywood or hurricane shutters on their windows, and some locals groused about the change in the forecast.
>> VIDEO: National Hurricane Center update on Irma
>> VIDEO: Daytona Beach as Irma approaches
"For five days, we were told it was going to be on the east coast, and then 24 hours before it hits, we're now told it's coming up the west coast," said Jeff Beerbohm, a 52-year-old entrepreneur in St. Petersburg. "As usual, the weatherman, I don't know why they're paid."
Tampa has not been struck by a major hurricane since 1921, when its population was about 10,000, National Hurricane Center spokesman Dennis Feltgen said. Now the area has around 3 million people.
The new course threatened everything from Tampa Bay's bustling twin cities of Tampa and St. Petersburg to Naples' mansion- and yacht-lined canals, Sun City Center's sprawling compound of modest retirement homes, and Sanibel Island's shell-filled beaches.
With the new forecast, Pinellas County, home to St. Petersburg, ordered 260,000 people to leave.
Irma has left more than 20 people dead in its wake across the Caribbean, ravaging such resort islands as St. Martin, St. Barts, St. Thomas, Barbuda and Antigua.
Irma weakened slightly in the morning but was expected to pick up strength again before hitting the Sunshine State.
Meteorologists predicted its center would blow ashore Sunday in the perilously low-lying Florida Keys, then hit southwestern Florida and move north, plowing into the Tampa Bay area. Though the center is expected to miss Miami, the metro area will still get pounded with life-threatening hurricane winds, Feltgen said.
On Saturday morning, the state was already beginning to feel Irma's muscle. Nearly 25,000 people had lost power, mostly in the Miami area, as the wind began gusting.
In Key West, 60-year-old Carol Walterson Stroud sought refuge in a senior center with her husband, granddaughter and dog. The streets were nearly empty, shops were boarded up and the wind started to blow.
"Tonight, I'm sweating," she said. "Tonight, I'm scared to death."
In one of the biggest evacuations ever ordered in the U.S., about 6.3 million people in Florida - more than one-quarter of the state's population - were warned to leave, and 540,000 were directed to clear out from the Georgia coast.
Gas shortages and gridlock plagued the evacuations. Parts of interstates 75 and 95 north were bumper-to-bumper.
Major tourist attractions, including Walt Disney World, Universal Studios and Sea World, all prepared to close Saturday. The Miami and Fort Lauderdale airports shut down, and those in Orlando and Tampa planned to do the same later in the day.
With winds that peaked at 185 mph (300 kph), Irma was once the most powerful hurricane ever recorded in the open Atlantic. But given its mammoth size and strength and its projected course, it could still prove one of the most devastating hurricanes ever to hit Florida and inflict damage on a scale not seen here in 25 years.
It could also test the Federal Emergency Management Agency's ability to handle two crises at the same time. FEMA is still dealing with aftermath of catastrophic Hurricane Harvey in the Houston area.
Ray Scarborough and girlfriend Leah Etmanczyk left their home in Big Pine Key and fled north with her parents and three big dogs to stay with relatives in Orlando. Scarborough was 12 when Hurricane Andrew hit in 1992 and remembers lying on the floor in a hall as the storm nearly ripped the roof off his house.
"They said this one is going to be bigger than Andrew. When they told me that, that's all I needed to hear," said Scarborough, now a 37-year-old boat captain. "That one tore everything apart."
Andrew razed Miami's suburbs with winds topping 165 mph (265 kph), damaging or blowing apart over 125,000 homes. The damage in Florida totaled $26 billion, and at least 40 people died.
Galofaro reported from Orlando. Associated Press writers Seth Borenstein in Washington; Terry Spencer in Palm Beach County; Gary Fineout in Tallahassee, Terrance Harris in Orlando; and Jason Dearen and David Fischer in Miami contributed to this report.