Tropical storm Isaac set its sights on the Dominican Republic and prompted fears it could affect the Republican National Convention in Tampa, Fla. In its 5 p.m. EDT Wednesday advisory, the National Hurricane Center in Miami said the storm, with sustained winds of 40 mph, was 180 miles south-southwest of San Juan, Puerto Rico, and 255 miles southeast of Santo Domingo, Dominican Republic, as it traveled west-northwest at 16 mph toward the coast of the Dominican Republic. Hurricane warnings were posted for Haiti and the south coast of Dominican Republic from Isla Saona westward to the Haiti-Dominican Republic southern board. The government of the Bahamas issued a tropical storm warning for the southeastern Bahamas and the government of Cuba issued a tropical storm watch for parts of the island. Isaac could become a hurricane Thursday night or Friday, forecasters said. Tropical storm-force winds extended outward from Isaac\'s center 140 miles. Isaac could generate 4- to 8 inches of rain over the northern Windward Islands and Leeward Island, the center said. Puerto Rico and the Virgin Islands could get 1-3 inches of rain with up to 6 inches possible.