With the window closing fast for anyone wanting to escape, Florida's governor issued urgent warnings to a third of his state's residents to evacuate as Irma - the massive hurricane on track to be the state's most catastrophic ever - hurtled toward Florida with 125 mph winds Saturday.

Gov. Rick Scott says the entire west coast of Florida will likely see dangerous affects from storm surge as Hurricane Irma comes ashore Sunday. About 6.3 million of the state's approximately 21 million residents have been asked to evacuate.

During a Saturday news conference, he told those in evacuation zones: "You need to leave — not tonight, not in an hour, right now," warning residents ahead of the storm's predicted arrival on Sunday morning.

Scott said that the storm surge is expected to be up to 15 feet (4.5 meters) in some areas along the west coast of Florida. In the Tampa Bay area, Scott said the storm surge could be between 5 feet (1.5 meters) and 8 feet (2 meters).

Scott said: "This is the most catastrophic storm the state has ever seen."

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.

"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."

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."

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.