MIAMI -- Florida Keys residents were urged Friday to follow tourists in fleeing the island chain as the powerful Hurricane Wilma made an agonizingly slow approach to the state. Many people in the Naples area were also told they should start leaving.

Monroe County officials encouraged residents "to voluntarily evacuate because of the potential of overcrowded highways" ahead of the storm expected to hit Florida on Monday. A mandatory evacuation will be announced once they have a better idea when Wilma's winds will reach the low-lying chain.

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Collier County's mandatory evacuation order begins at noon and covers areas south and west of U.S. 41 , emergency management spokeswoman Jaime Sarbaugh said. That zone includes downtown Naples and the wealthy snowbird enclave of Marco Island, but she did not know how many people were covered.

"We think people are really listening this year. People are already following voluntary evacuation orders," she said. "We hope people continue to heed the advice. Your life is much more important than your things."

Early Friday, northbound traffic on Interstate 75 leaving the Naples and Fort Myers area was backed up for at least 10-15 miles in one section of the highway.

Monday Landfall Predicted

Forecasters at the National Hurricane Center in Miami said Friday that Florida's agonizing wait for Wilma would continue as the hurricane was expected to hover around Mexico's Yucatan Peninsula longer than previously thought. Parts of the 145-mph hurricane's eyewall had moved over the Yucatan.

Landfall somewhere on Florida's western coast was not likely until sometime Monday afternoon, forecasters said. Wilma will likely linger over the Yucatan for a few days, National Hurricane Center Director Max Mayfield said Friday.

"If it stays over the Yucatan for any significant length of time and much of the circulation is over land ... that would obviously be terrible news for Mexico, but for the United States interests it means that we'll have a weaker hurricane coming out into the Gulf of Mexico and it will be slower in getting here," Mayfield said at a news conference.

Wilma could weaken from a Category 4 to a Category 3 or less before making landfall in the United States, he said. But he stressed that Wilma probably would still be a strong hurricane with a high storm surge when it reaches Florida.

"This is Friday, we're heading into a weekend and the message is that we really want everybody in the Florida Keys and the southern portions of the Florida peninsula to pay very, very close attention to this," he said.

In Key West, the slowdown meant that many residents didn't have much to do Friday because tourists were gone. Many have already prepared their homes.

"There's time to do nothing, everything's closed. I'm just sitting around," said Brad Holland, who made some last minute preparations at the ice cream shop where he's the manager.

Authorities took advantage of the unexpected extra day to stockpile emergency supplies.

Gov. Bush Declares State Of Emergency

Gov. Jeb Bush declared a state of emergency Thursday. He said the state had food, water, ice and other supplies ready and disaster-response teams that included up to 7,500 National Guard members standing by.

"We are battle-tested, well-resourced, well-trained," he said.

Max Mayfield, director of the hurricane center, said the slowdown would give Wilma time to weaken from a Category 4 storm with sustained 145 mph winds to a Category 3 or less before making landfall in the United States.

But he stressed that Wilma probably would still be a strong hurricane with a powerful storm surge when it reaches Florida.

Wilma was expected to make a turn to the northeast toward Florida after striking Mexico's Yucatan Peninsula in the western Caribbean Sea.

Mayfield said Wilma is unusually large, with an eye 35 miles wide and tropical storm-force winds extending out some 200 miles from the center that could cause widespread damage.

"Don't just focus on the eye of the hurricane," Mayfield said.

State meteorologist Ben Nelson warned that Wilma could produce a storm surge of 12 to 17 feet.

Latest Advisory

At 11 a.m. EDT, the center of Wilma's eye was about 35 miles southeast of Cozumel, Mexico, and about 425 miles southwest of Key West, according to the hurricane center. It was heading northwest at about 5 mph toward the Yucatan Peninsula, where Mayfield predicted it could do catastrophic damage.

Although Wilma was expected to approach Florida from the west, forecasters warned that major cities on the peninsula's Atlantic Coast, including Miami, Fort Lauderdale and West Palm Beach could be hit by strong winds and heavy rains.

The Federal Emergency Management Agency was positioning emergency materials in Jacksonville, Lakeland and Homestead. FEMA acting chief R. David Paulison said the agency has 150 truckloads of ice and 150 truckloads of water, and the Red Cross has 200,000 meals available.

"We are ready for the storm, as much as you can be," Paulison said in Washington.

The governor urged people not to hoard gasoline, which frequently causes long lines at gas stations and some to run out of fuel. Bush said an estimated 200 million gallons of fuel were available at Florida ports, enough for an adequate supply.

Wilma was on a path that could threaten areas hit by Hurricane Charley in August 2004. Some houses and businesses in the area are still boarded up because of that storm.

Wilma Was Strongest Hurricane Recorded

At one point early Wednesday, Wilma was the most intense hurricane recorded in the Atlantic as measured by its pressure. The storm's pressure dropped to 882 millibars, the lowest reading ever in an Atlantic-basin hurricane. Typically, the lower the pressure, the faster the sustained wind.

The previous strongest Atlantic storm on record, based on pressure readings, had been Hurricane Gilbert in 1988, which registered 888 millibars.