Hurricane Frances, a 300-mile-wide menace, whipped over the Bahamas on Thursday and whirled toward Florida, prompting the evacuation of as many as 2.5 million people in a state still struggling to recover from the ravages of Hurricane Charley.

Residents clogged Florida's highways as they hoped to find refuge before the arrival of Frances, a bigger storm than Charley. Frances weakened slightly late Thursday into a Category 3 storm, but still featured 125-mph winds as it headed for the state's heavily populated eastern coast. The storm's outer bands were expected to bring heavy winds and rain to southeastern Florida by Friday. The core was predicted to come ashore near Vero Beach on Saturday, though forecasters said its course could vary.

Emergency officials opened shelters in counties in a hurricane advisory zone that stretched north almost to the Jacksonville area and south to Florida City, below Miami. The area covers 14.6 million of the state's 17 million residents.

Gov. Jeb Bush (R) asked his brother, President Bush, to declare Florida a disaster area.

"This storm will have significant force to it," Jeb Bush said.

The storm is expected to be the most powerful since Hurricane Andrew in 1992, which killed 26 people and was one of the region's most devastating hurricanes in the last half of the 20th century. A one-two punch of Charley and Frances would mark the first time in 54 years that two storms packing such a wallop have struck Florida within weeks of one another.

Charley charged ashore on Florida's Gulf Coast on Aug. 14, killing 27 people and inflicting billions of dollars in damage to homes and businesses. Only about one-fifth of the debris had been cleared as of this week, emergency officials said. As of Wednesday, the Federal Emergency Management Agency had doled out $86.4 million in Charley-related aid. More than 176,000 residents had signed up for assistance.

"Charley had a significant impact on this state, and now you've got Frances coming," said Peter Teahen, a spokesman for the American Red Cross, which has housed more than 101,000 victims in 250 shelters and has spent $50 million on relief efforts in Charley's wake. "You have people who are already exhausted physically and emotionally. They are emotionally spent, and they are still a long ways from recovering from Charley. And now they are going to get hit again."

The vivid reminder of the power of such storms sent residents flocking into stores Thursday to snap up hurricane essentials such as plywood, gasoline, water, canned food and portable generators. By mid-afternoon, horns blared in traffic at South Miami's Red Bird Shopping Plaza, where customers waited in long lines before hauling cases of water and beer through congested parking lots.

Carlos Moreno, 45, a schoolteacher, waited more than an hour to refill his propane tanks.

"If we lose power, we will be grilling outdoors with these," Moreno said. "Andrew made us more aware. I'm better prepared this time. I've got coolers filled with ice, plenty of food and a gas grill now. Then, people took it for granted that it would miss us. . . . . [Y]ou have to take it seriously."

In Walgreen's, pharmacist Carla Wertman kept her sense of humor even as she put in extra hours to fill prescriptions for the dozens of customers in line. "It's been busy all week, but today is the worst," she said. "We will be open all night and possibly closing sometime tomorrow."

At Miami International Airport, chaotic on the best of days, the scene was approaching full-scale frenzy. Anxious travelers checked their watches, fretting they would miss their flights as the afternoon waned and lines grew longer.

"People are desperate," said David Gomez, an American Airlines agent.

Meanwhile, FEMA teams stockpiled ice, water, meals and tarpaulins for distribution in regions in the storm's path. Federal and state officials placed emergency medical personnel and search-and-rescue teams on alert, and laid plans to open disaster field offices and assistance centers in the hardest-hit areas.

Officials urged residents who did not evacuate to buy extra water and nonperishable food, store extra ice in freezers and keep battery-powered radios handy to hear emergency broadcasts if power is knocked out.

"We were successful with Charley, because we were massive, overwhelming and fast," said Michael D. Brown, the FEMA director. "For this event I want us to be massive, overwhelming and fast squared."

For some, it was all a bit much.

On Miami Beach, cafe life refused to stop. Beneath the verandas of the art deco hotels on Ocean Drive, sunburned tourists and cheeky locals ordered tropical drinks. Asking for a hurricane, a potent alcoholic concoction, was a sure laugh line at many bars, where an aura of zaniness competed with one of anxiety before the storm.

John and Nancy Swanton, a Tampa couple celebrating their 16th wedding anniversary at the Pelican Cafe, turned to the local television anchors for amusement.

"It's 'the sky is falling, Chicken Little,' " said John Swanton, 43, a real estate investor.

"The news is so sensational!" said his wife, 44, a retired tobacco saleswoman. "It's so fun to watch. So entertaining."

Tampa was expected to be directly in the path of Hurricane Charley. But the storm veered south, turning Punta Gorda, a sleepy retirement community on Florida's west coast, into a national household name. Tampa residents who evacuated to Orlando left a place that went unscathed and put themselves in harm's way.

Now the Swantons wondered whether Frances would be similarly fickle. They might flee Miami Beach on Thursday afternoon, only to drive directly into the storm's path.

"We could be driving right into it," Nancy Swanton said.

Lee reported from Washington. Special correspondent Catharine Skipp contributed to this report.

Jennie Amsel, 104, far left, and Patricia Henkel, third from left, are helped from a Miami Beach assisted-living facility before the arrival of Frances.