MIAMI — Hurricane Sandy began what could be a long and damaging march out of the Caribbean on Wednesday, leaving a string of Jamaican towns flooded and at least one man dead, crushed by a boulder. In northern Haiti, one person died while crossing a swollen river.

Sandy was far from done. At 11 p.m., the National Hurricane Center said its winds had strengthened to 90 mph and it could intensify further before it struck eastern Cuba. Next up: The Bahamas and — at least potentially — the Northeast United States where some computer models predict Sandy could lose its tropical characteristics but still morph into a monster “nor’easter” slamming the coast sometime next week.

Florida, fortunately, was expected to dodge a direct hit and serious disruption from Sandy, though Palm Beach County decided to close schools early Thursday and cancel classes Friday. Miami-Dade and Broward Counties planned to follow regular schedules, although Broward canceled outdoor events both days.

The NHC placed much of the coastline from the Middle Keys to Flagler Beach under tropical storm warnings and watches. Forecasters expect Sandy to weaken after crossing Cuba, but its wind field could expand enough for outer bands and gusts of tropical storm force to brush the South Florida coast. Still, its projected path through the Bahamas should keep the strongest winds of its “dirty side” well offshore.

The forecast for South Florida calls for foul weather, with the worst coming Thursday night and Friday: steady 25- to 35-mph winds with gusts to 50 mph, 15-foot swells and heavy surf that could cause beach erosion and strong thunderstorms.

In Jamaica, where Sandy made landfall at 3 p.m. near the densely populated capital of Kingston, damage was mounting. The Associated Press, citing police, said at least one person had been killed, an elderly man crushed by a boulder that rolled over his clapboard house.

Storm surge and heavy seas swamped waterfront homes in the eastern Kingston neighborhood of Caribbean Terrace and the road to Kingston’s major airport. Flood water breached rivers and retaining walls, cutting off some communities, including Kintyre in the St. Andrew Parish, according to The Daily Gleaner newspaper. In St. Mary Parish on the northern coast, directly under Sandy’s fierce core, resident Pamella Simms said power was out well before the storm reached the coast.

“Several trees have fallen and many houses have lost their roofs. And we are in darkness,” Simms said.

In Portland, another eastern parish prone to flooding, several roads were already impassable, blocked by landslides and downed trees, and flood waters were rising. With 6 inches to a foot of rain projected across the mountainous island, and up to 20 inches in spots, flash floods and mudslides remained a threat. “We are just recovering from the effects of heavy rains a few weeks ago, and here comes Sandy,” said Rackell Wilson, a nurse who lives in the area.

In Haiti, Sandy’s rain-laden outer bands triggered extensive flooding. Rivers were rising across the country. Farms were under water in Ille a Vache, a small island off the southwestern tip of Haiti. Homes were flooded in the fishing village of Tiburon and in the southwestern city of Les Cayes, where 50 patients were evacuated from a hospital along with 200 residents in a seaside settlement.

One woman was reported killed in the southern town of Camp Perin as she crossed a rising river, said Edgard Celestin, spokesman for the Office of Civil Protection.

Marie-Alta Jean Baptiste, director of the Office of Civil Protection, urged residents to stay away from rivers “to prevent any additional deaths.”

The South Florida Water Management District was preparing for heavy rains and potential flooding, although no repeat of the deluge from Tropical Storm Isaac was expected. Southeast Florida already has received near-record amounts of rain this year.

Robert Molleda, a meteorologist with the National Weather Service’s Miami office, said storms could produce between 1 and 3 inches of rain — but probably not across the entire region. “It’s going to be a close call whether any substantial rain bands do make it on shore,” he said.

At the U.S. Navy base at Guantanamo Bay, Cuba, no evacuations were planned but sirens wailed across the base warning of coming dangerous winds. Guards moved some prisoners from a wood hut to a steel and cement building.

Sailors made preparations while an Army colonel went forward with a pretrial hearing in the death-penalty case against Abd al Rahim al Nashiri, 47, accused of masterminding al-Qaida’s October 2000 suicide bombing in Yemen of the USS Cole.

CBS News, meanwhile, reported that the Cuban government had ordered an evacuation of low-lying areas along the eastern coast and a cleanup of storm drainage systems in the area.

Once it clears the Bahamas late Friday, Sandy’s future is less certain. Dennis Feltgen, a spokesman for the hurricane center, said computer models remain split on whether it will turn harmlessly out into the Atlantic Ocean or curve west toward the Northeast Coast as a still-powerful but nameless “extra-tropical” storm.