The watch was issued early Monday from Deerfield Beach, near Boca Raton, southward along the east coast, and from Chokoloskee southward on the west coast, meaning hurricane conditions could develop in the area within 36 hours. The Keys were put under a watch on Sunday afternoon.
At 5 a.m. EDT, Ernesto, the fifth named storm of the Atlantic hurricane season, had maximum sustained winds of 50 mph and was 600 miles southeast from the Keys. It was moving northwest at 12 mph.
Gov. Jeb Bush issued a state of emergency Sunday for all of Florida. Immediate concern centered on the Keys, where visitors were ordered out and plans were enacted to evacuate special-needs residents to Miami.
"We do expect it to reach the Gulf, maybe as a Category 1 hurricane, possibly a Category 2," said John Cangialosi, a meteorologist with U.S. National Hurricane Center in Miami. "It's difficult to say where it will be, but in three days we're projecting it anywhere from the eastern Gulf near the Florida panhandle to the western Bahamas."
In the Keys, three shelters were set to open Monday. All travel trailers and recreational vehicles were ordered out of the Keys, and mobile home residents were also urged to evacuate.
Some residents of the low-lying island chain flocked to grocery stores and home-supply warehouses to stock up on canned goods, bottled water and other storm essentials.
"Key Westerners are used to this," said Jim Bernard, assistant manager at a Home Depot in Key West.
Dan Drum, 56, a contractor who has been living in Key West since 1977, was waiting when Home Depot opened early Monday. He said he was going to spend part of the day nailing more roofing screws to a property he owns in Sugarloaf Key.
"I just bought $55 worth of screws. That's all they had," he said.
Ernesto made it 1 mph above the 74-mph threshold to be a hurricane Sunday, but weakened as it plodded toward Cuba's southeastern corner. Still, the hurricane center cautioned that Ernesto may strengthen significantly as it moves toward Florida.
"It has a good chance to regain hurricane status," said Max Mayfield, director of the National Hurricane Center.
The state of emergency directs counties to activate their emergency management offices and activates the National Guard, among other things. Bush canceled several meetings scheduled in New York on Monday, and will remain in Tallahassee to monitor storm developments.
Ernesto lashed Haiti and the Dominican Republic on Sunday and threatened to bring as much as 20 inches of rain to parts of Haiti, where it claimed at least one life. The storm was expected to move over Cuba, then bring rain and wind toward Florida, forecasters said.
"You don't know where to go. You don't know where it's going to blow," said tourist Jim Rogers of Lodi, N.J., who spent Sunday preparing to leave the Keys. "You don't want to be in Key West."
Florida's emergency management center in Tallahassee was partially activated Sunday, and several counties around the state were expected to follow suit Monday. Emergency officials encouraged people across the state to monitor the storm, check emergency supplies and disaster plans — a familiar theme, considering seven hurricanes have hit Florida and one has brushed by in the past two years.
"Ernesto bears watching," said Mike Stone, spokesman for the Florida Division of Emergency Management.