Two babies were killed when a river surging with rain from the storm toppled their overcrowded bus, a U.N. official said, raising the storm's Caribbean death toll to at least 14.
In Florida, roughly 25,000 tourists had evacuated, Monroe County Mayor Mario Di Gennaro said, but some bars and restaurants were doing business, even if crowds were considerably thinner.
Forecasters said Fay is expected to near hurricane strength, which starts at windspeeds of 74 mph, when it reaches the Keys.
The exact track is not clear but the storm is expected to hit the Keys first and then sweep up the western coast of Florida, forecasters said. It could strengthen into a Category 1 storm after it moves past the Keys.
Fay is expected to increase the possibility of tornadoes as it moves across Florida, reports The Early Show weather anchor Dave Price. Residents in the storm's path are gassing up and sandbagging.
Five hundred National Guardsmen have been activated but not dispatched, adds Price. Officials say this storm can do damage even far away from its center.
Traffic leaving Key West and the Lower Keys remained light but steady. Monroe County Sheriff Rick Roth said the 110-mile, mostly two-lane Overseas Highway would likely remain open during and after the storm, but he urged people not to travel once Fay hits.
Just before 2 p.m. EDT Monday, the storm's center was approaching Key West across the Florida Straits between Cuba and the Keys. The center was about 20 miles southeast of Key West and the storm was moving toward the north-northwest near 14 mph.
Maximum sustained wind speeds were near 60 mph with higher gusts, and the storm was expected to strengthen over the next 24 hours to hurricane strength.
While tourists caught the last flight out of town and headed out of the storm's path, residents in the carefree Florida Keys were putting up hurricane shutters and checking their generators, but not doing much more.
"We're not worried about it. We've seen this movie before," said 58-year-old Willie Dykes, who lives on a sailboat in Key West and was buying food, water and whiskey.
By midafternoon, heavy rains moving ahead of Fay's core were pelting the low-lying Keys island chain. Sustained winds of about 33 mph bent palm trees, and some gusts hit 51 mph.
The sixth named storm in the Atlantic hurricane season was expected to become a hurricane before curling up the state's western coast and hitting Florida's mainland sometime Tuesday.
"There are bad storms and there are nice ones, and this is a nice one," said Becky Weldon, a 43-year-old guest house manager in Key West. "It cleans out all the trees, it gives people a little work to do and it gets the tourists out of here for a few days."
Officials were worried that complacency could cost lives, repeatedly urging people across the state to take Fay seriously. The message got through to tourists - Monroe County Mayor Mario Di Gennaro estimated 25,000 fled the Keys. Some residents have taken steps since the busy 2004-05 storm years, when eight hurricanes hammered Florida, such as buying generators and strengthening homes, but not everyone is as prepared.
"This is not the type of storm that's going to rip off a lot of roofs or cause the type of damage we normally see in a large hurricane," said Craig Fugate, the state's emergency management chief.
However, Fugate said: "I've seen as many people die when I have a blob-shaped asymmetrical storm that they dismiss as not being very dangerous."
The state took every step to make sure it was ready. National Guard troops were at the ready and more were waiting in reserve, and 20 truckloads of tarps, 200 truckloads of water and 52 truckloads of food had arrived.
One who did heed the call to prepare was Chris Fleeman, a 35-year-old mechanic on Big Pine Key who was busy helping friends and family members seal up their homes.
"I've got a generator and I've got a concrete home that I built myself, so I know it can withstand this," Fleeman said.
Since 2006, Florida has taken several steps to make sure its residents are prepared. More than 400,000 houses were inspected under a program that provides grants to people to strengthen their houses.
Florida law also now requires some 970 gas stations along hurricane evacuation routes statewide to have backup generators so they can keep pumping gas if the power goes out. Many utilities also have installed stronger power poles.
"Every hurricane that we have, we have additional lessons learned and experience," said U.S. Sen. Bill Nelson, D-Fla.
As it moved though the Carribean, Fay was blamed for at least eight deaths in Haiti and the Dominican Republic, including two babies who were found in a river after a bus crash.
It passed over the Keys around 3 p.m. on Monday, and a hurricane watch was in effect for most of the Keys and along the state's west coast, with a tropical storm warning in effect in the east from Sebastian Inlet southward. Maximum sustained wind speeds were near 60 mph with higher gusts.
No damage or injuries were immediately reported in the Keys, where a few bars and restaurants stubbornly remained open. Authorities said a possible tornado knocked down a tree on Big Coppitt Key and there were scattered power outages as well as local street flooding.
Between 4 and 10 inches of rain is possible across mainland Florida, so flooding is a threat even far from where the center comes ashore, said Stacy Stewart, a senior hurricane specialist at the National Hurricane Center.
"This is a broad, really diffuse storm. All the Florida Keys and all the Florida peninsula are going to feel the effects of this storm, no matter where the center makes landfall," he said. "We don't want people to downplay this."
Farther north, residents were not so sanguine. In Punta Gorda - a Gulf Coast community hit hard by Hurricane Charley in 2004 - the sounds of drills were in the air as business owners attached aluminum storm shutters to windows and doors Monday afternoon.
The very idea of an August storm frightens residents there, especially those who rode out the compact but powerful Category 4 hurricane four years ago.
"I am scared," said Monica Palanza, a Punta Gorda real estate agent who remembers seeing trees topple on her neighbors' homes in 2004. "You can never be prepared enough."