MIAMI (Reuters) - Tropical Storm Ernesto kept on a westerly course in the Caribbean Sea on Saturday and will soon bulk up into a hurricane that may soak Jamaica as it passes by the island, U.S. forecasters said.
Officials in Jamaica issued a tropical storm warning as Ernesto moved in open waters at 18 miles per hour on a predicted track that should keep it at sea until a forecast landfall in Mexico's Yucatan Peninsula on Wednesday.
With maximum sustained winds falling back to 50 mph (85 kmh), Ernesto on Saturday afternoon was 270 miles south of Santo Domingo in the Dominican Republic and was expected to stay clear of Jamaica and Hispaniola, the mountainous island Haiti shares with the Dominican Republic.
Tropical storm conditions would strike Jamaica on Sunday afternoon, while the southern coasts of Puerto Rico and Hispaniola will see squalls on Saturday, U.S. forecasters said.
Three to 6 inches were expected in Jamaica. Showers and thunderstorms - sometimes severe - were possible on the islands of Aruba, Curacao and Bonaire off Venezuela's northern coast.
"The center of Ernesto should pass south of Hispaniola tonight and south of Jamaica on Sunday evening," the U.S. forecasters in Miami said. "Ernesto is forecast to become a hurricane in the northwestern Caribbean in a day or two."
Ernesto, which did no reported damage on Friday as it passed over the tiny island of Saint Lucia, would be deemed a hurricane if its winds reach 74 mph.
Forecasters expect Ernesto to move into the southern Gulf of Mexico by Thursday but it was too early to know whether it could disrupt oil and gas operations in the gulf.
U.S. National Hurricane Center forecasters said another tropical storm, called Florence, formed on Saturday in the eastern Atlantic and was moving west in open waters. As of late morning, forecasters said, Florence was about 415 miles (665km) west of the southernmost Cape Verde Islands.
With maximum sustained winds of 45 mph (75 kmh), Florence was the sixth named storm of the Atlantic-Caribbean hurricane season, moving west at 16 mph, and was expected to track westerly before weakening next week.
August and September are usually the most active months of the Atlantic-Caribbean hurricane season, which runs from June 1 to November 30.
Reporting By Michael Connor in Miami; Editing by Bill Trott