Kingston, Jamaica ? Tropical Storm Ernesto gathered strength as it steamed through the central Caribbean toward Jamaica on Saturday and threatened to enter the Gulf of Mexico as the first hurricane of the 2006 Atlantic season.

Ernesto could grow into a Category 3 hurricane by Thursday, menacing a broad swath of the Gulf Coast including hurricane-ravaged New Orleans, the U.S. National Hurricane Center in Miami forecast. Category 3 hurricane Katrina struck the city a year ago Tuesday.

“It looks likely that it will hit (the U.S.), but it’s way too soon to say where” or how much impact it would have, said John Cangialosi, a meteorologist with the hurricane center. “At this point, keep a close eye, anyone in the Gulf Coast, and just keep monitoring this.”

Standing in the hurricane’s path, Jamaica, the Cayman Islands and Cuba issued hurricane watches as the storm’s winds grew to 60 mph late Saturday. It was forecast to become a hurricane as early as this evening while it passes near Jamaica, Cangialosi said.

Ernesto’s course would bring it over Jamaica by this afternoon, dumping 4 to 8 inches of rain on the island with up to a foot possible in some areas, the hurricane center said. Fisherman were warned to return to shore – with tides of up to 3 feet 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.

In Haiti, emergency officials went on local radio to warn people living in flimsy 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 – which could cause life-threatening flash floods and mud slides.