Hurricane warnings were posted for the Cayman Islands, Jamaica, Haiti and eastern Cuba, including the U.S. Navy base at Guantanamo Bay, where some 520 terror suspects are detained. Forecasters also warned Dennis was on track for the Alabama-Florida coastline.
Dennis came right behind Tropical Storm Cindy, which made landfall late Tuesday in Louisiana and hindered oil production and refining. Traders said that uncertainty over both storms helped to push oil prices to new highs.
Packing sustained winds near 105 mph, the fourth storm of the Atlantic season — and its first hurricane — could dump up to 15 inches of rain over mountains in its path, including Jamaica's coffee-producing Blue Mountains, according to the U.S. National Hurricane Center in Miami.
At 8 a.m. EDT, Dennis was about 130 miles east-southeast of Kingston, Jamaica.
Last year three hurricanes — Frances, Ivan and Jeanne — tore through the Caribbean with a collective ferocity not seen in many years, causing hundreds of deaths and billions of dollars in damages.
Inside the detention center at Guantanamo Bay, the military prepared audio tapes in at least eight languages warning that a storm was coming and heavy steel shutters would be closed on some cell windows, said Col. Mike Bumgarner.
Military officials had no immediate plans to evacuate troops or detainees at Camp Delta, which is about 150 yards from the ocean but was built to withstand winds up to 90 mph, according to Navy Cmdr. Anne Reese, supervisor of camp maintenance and construction.
Power lines could be knocked down and roofs could be damaged on some older, wooden buildings, Reese said.
"It will be bad, but it's not going to be very destructive," she said.
Bumgarner said the military had a contingency plan to move the prisoners if conditions became serious.
Poverty-stricken Haitians said there was little they could do about the warnings this time.
"It's not only that we don't have money to prepare, we don't have money either to eat. We are willing to stay here and let whatever happens happen," said Martine Louis-Pierre, a 43-year-old mother of three.
At 8 a.m. EDT, the storm was centered about 130 miles southeast of Kingston, Jamaica, and 165 miles south of Guantanamo, moving northwest in the past few hours at about 10 mph, but overall west-northwest at about 13 mph, the Hurricane Center said.
With winds at 105 mph, Dennis was upgraded to a Category 2 hurricane. It became a Category 1 hurricane Wednesday afternoon.
Private forecaster AccuWeather has the storm tracking into the eastern Gulf of Mexico, with landfall Friday or Saturday on the Florida-Alabama border as a strong Category 2 or Category 3 hurricane, with winds from 96 mph to 130 mph.
Radio stations in Haiti and Jamaica warned people to stay away from rivers that could overflow their banks.
"Particularly in the morning, the conditions will begin to deteriorate," Navy Lt. Dave Roberts, a meteorologist at the National Hurricane Center, told CBS Radio News. "The tropical storm-force winds in the next few hours should begin to reach the eastern extremes of Jamaica."
Some southern roads in Haiti, which is dangerously deforested, already were blocked by flooding Wednesday.
In southern Les Cayes, Jose Luis Paez, assistant chief of operations for U.N. civilian police, said 600 civilian police were trying to evacuate people from low-lying areas, but some refused to leave.
Jasmine Romelus, a 22-year-old student, was among them. "Hurricane?" she asked. "They always say there's going to be a hurricane and it never comes."
Six small communities in the eastern Jamaica parish of St. Thomas were also cut off by flood waters. Emergency officials urged coastal residents — a large percentage of the population of 2.6 million — to move inland and ordered schools closed until Friday so they could be used as shelters. Kingston's airport was also closed.
Jamaica's Prime Minister P.J. Patterson abandoned the final day of the annual Caribbean summit in St. Lucia, to rush home. Before leaving, he called on Jamaicans to prepare "to protect those who are infirm, the elderly and the young."