Updated

Tropical Storm Ernesto gathered strength — and inspired increasing worries — as it steamed toward Jamaica and western Haiti, and forecasters predicted it could turn into the first hurricane of the 2006 Atlantic season as early as Sunday.

In Washington on Saturday, the U.S. Department of Homeland Security expressed concern at projections that Ernesto could grow into a Category 3 hurricane by Thursday, menacing a broad swath of the Gulf Coast, including hurricane-ravaged New Orleans.

But it was too soon to say how much impact it would have there, said John Cangialosi, a meteorologist with the U.S. National Hurricane Center in Miami.

"It looks likely that it will hit, but it's way too soon to say where," he said.

"At this point keep a close eye, anyone in the Gulf Coast, and just keep monitoring this," Cangialosi said.

Click Here for the National Hurricane Center Forecast

Jamaica, the Cayman Islands and Cuba — all in the hurricane's path — issued hurricane watches as the storm's winds grew to near 60 mph (95 kph) early Sunday. It was forecast to become a hurricane as it passes near Jamaica, Cangialosi said.

Ernesto's course would bring it over Jamaica by Sunday afternoon, dumping 4 to 8 inches (10 to 20 centimeters) of rain on the island with up to a foot (30 centimeters) possible in some areas, the hurricane center said. Fisherman were warned to return to shore — with tides of up to 3 feet (1 meter) above normal expected.

Similar rainfall and tides were possible for Haiti.

Jamaica's Prime Minister Portia Simpson Miller put the country's security forces on alert and said at a press conference Saturday that all the island's shelters were open.

"Ensure that the children are not left alone and make it easier for rescue workers," she said.

Jamaica issued advisories by radio and television for residents in low-lying areas across the island to be prepared to evacuate if necessary.

The fifth named storm of the Atlantic hurricane season was centered about 130 miles (215 kilometers) south-southwest of Port-au-Prince, Haiti and 285 miles (455 kilometers) east-southeast of Kingston. It was moving west-northwest at about 9 mph (15 kph).

Heavy showers hit Kingston on Saturday afternoon, causing traffic jams as motorists tried to reach stores and people waited in long lines at supermarkets, filling grocery carts with canned goods, batteries and candles.

"It's nature and we can't stop it from taking its course," said taxi driver Patrick Wallace, 55, as he left a supermarket laden with canned goods.

Christine Williams, a manager at a Kingston hardware store, said people were scooping up material to protect their homes.

"They are buying mainly tarpaulin, plywood and building material. We haven't stopped cashing (ringing people up) from morning," she said.

Despite sunny skies in the British territory of the Caymans, people packed gas stations, hardware stores and supermarkets, and formed big lines to withdraw money from cash machines. Businesses also boarded up.

Debbie Curigliano, of Bridgeville, Pennsylvania, said she and her husband would ride out the storm at their resort in Seven Mile Beach.

"I am sure they (the hotel) have been through this before, so I am going to put all my faith in the hotel and I am sure they will guide me right through it," she said.

In Haiti, emergency officials went on local radio to warn people living in shantytowns on the southern coast to seek shelter in schools and churches. The hurricane center said Haiti and the Dominican Republic could get up to 20 inches of rain in some places.

"These people could be in great danger," said Adel Nazaire, a coordinator with Haiti's civil protection agency. "Flooding is the biggest concern because a lot of residents live along the rivers and the sea."

The impoverished Caribbean nation is 90 percent deforested, increasing vulnerability to deadly flooding and mudslides.

Fears that the storm could damage offshore energy facilities in the Gulf of Mexico sent oil and natural gas prices higher.

BP PLC said it would evacuate some 800 of its 2,400 workers from the Gulf of Mexico by late Saturday due to the storm. The evacuated workers are not essential staff, most associated with long-term projects that have not begun producing, BP spokesman Hugh DePland told Dow Jones Newswires.

Meanwhile, former Tropical Storm Debby, now a depression with maximum winds of 30 mph (48 kph), was expected to stay over the open Atlantic, posing only a threat to ships. At 5 p.m., the center of the storm was about 1,410 miles (2,270 kilometers) west-southwest of the Azores.