San Juan, Puerto Rico ? Tropical Storm Ernesto formed Friday over the Caribbean as it moved toward Jamaica and the Cayman Islands and could develop into the first hurricane of the 2006 Atlantic season, the U.S. National Hurricane Center said.

Ernesto was projected to reach hurricane strength early next week and to enter the Gulf of Mexico on Tuesday or Wednesday but it was too soon to predict whether it would hit the United States, said Robbie Berg, a forecaster with the hurricane center in Miami.

Jamaica, which stood straight in the storm’s path, issued a tropical storm watch, and Haiti issued a tropical storm watch for its southern coast.

The storm was on a course that would bring it over Jamaica by Sunday afternoon, dumping heavy showers. Fishermen were warned to return to shore and Prime Minister Portia Simpson Miller met with disaster agencies to prepare.