Hurricane Dean barreled across the eastern Caribbean Saturday and took aim at Hispaniola, Jamaica and Mexico's Yucatan Peninsula, with forecasters saying it could turn into a monster Category 5 storm within 72 hours.

With sustained winds now at 150 mph, Dean left behind floods, debris and at least three deaths on the islands of St. Lucia, Martinique and Dominica on Friday.

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The first hurricane of the Atlantic season, the Category 4 Dean was expected to gain power as it moves across the warm waters of the Caribbean through the weekend. The National Hurricane Center in Miami said its winds could surpass 155 mph as it approaches the Yucatan Peninsula and the Gulf of Mexico on Monday.

By Wednesday, there is a chance Dean could threaten the U.S., though it is expected to lose some of its punch as it travels over the Yucatan.

The immediate danger, however, comes Saturday as the storm passes south of Hispaniola, the island shared by the Dominican Republic and Haiti — both particularly prone to devastating floods.

The hurricane center issued a hurricane warning for the southern coast of the Dominican Republic early Saturday.

Haitian authorities issued an alert for coastal communities and ordered fishing boats to stay ashore until after the weekend. Prime Minister Portia Simpson-Miller of Jamaica — where a direct hit is expected Sunday — ordered shelters opened across the island and called for a halt to campaigning for the Aug. 27 elections.

"Let us band together and unite in the threat of this hurricane," Simpson-Miller said.

Earlier Friday, Dean roared across small eastern Caribbean islands.

In tiny St. Lucia, fierce winds tore corrugated metal roofs from dozens of homes and the pediatric ward of a hospital, whose patients had been evacuated hours earlier. Police spokeswoman Tamara Charles said a 62-year-old man was swept away and drowned when he tried to retrieve a cow from a rain-swollen river.

In Dominica, a woman and her 7-year-old son were killed when a rain-soaked hillside gave way and crushed the home where they were sleeping, said Cecil Shillingford, the national disaster coordinator.

French authorities on the adjacent island of Martinique said a 90-year-old man died of an apparent heart attack during the storm but he was alone and already dead when emergency medical personnel arrived and it was unclear whether Dean was a factor.

People in Martinique, St. Lucia and Dominica mostly stayed indoors Friday while Dean's remnants pounded the islands with heavy rain and authorities tried to assess damage.

Many who did venture out said they were surprised the islands seem to have gotten off fairly easy.

"I did not sleep at all last night and was a little worried that the roof of my house would be blown off with all that wind. Thank God it did not," Gwenie Moses said as she checked her small tin-roofed house in Dominica's capital, Roseau.

Dominica's government later reported at least 150 homes were damaged.

In St. Lucia, the storm scattered boulders from the sea onto downtown streets and knocked down trees. With utility poles downed, the power company turned off electricity across the island to prevent people from being electrocuted.

At 5 a.m. EDT, Dean was centered about 660 miles east-southeast of Kingston, Jamaica, and about 240 miles south of San Juan, Puerto Rico. It was moving west at 17 mph. The storm's maximum sustained winds were near 150 mph.

Dominica, which lies north of Martinique, had minor flooding, a few downed fences and trees and battered banana crops, one of the island's main exports.

At Ross University School of Medicine on Dominica, about 80 medical students, mostly from the U.S., and 20 staff and faculty members spent the night watching movies, playing games or sleeping on the floor between desks in a concrete building that was converted into a shelter.

On Martinique, an overseas department of France, many homes lost roofs, leaving people's belongings exposed to driving rain that fell even hours after the brunt of the storm had passed.

"We don't have a roof ... everything is exposed. We tried to save what we could," said Josephine Marcelus in the northern town of Morne Rouge. "We sealed ourselves in one room, praying that the hurricane stops blowing over Martinique."

Nearly 100 percent of Martinique's banana crops and 70 percent of its sugar cane was destroyed in the hurricane, said Christian Estrosi, France's junior minister for overseas territories.

It was too early to tell whether the storm would eventually strike the United States, but officials were gearing up for the possibility.

"It's so far out, but it's not too early to start preparing," said Katherine Cesinger, a spokeswoman for Texas Gov. Rick Perry.

Energy futures rose Friday on news that Dean could hit the Gulf of Mexico, which produces roughly 25 percent of America's oil and 15 percent of its natural gas. Royal Dutch Shell PLC said it would evacuate 275 nonessential personnel from the Gulf, adding to the 188 who left earlier this week before another tropical storm struck Texas.