Tropical Storm Irene Aug 21 2011

(CNN) -- Authorities posted hurricane warnings for Puerto Rico and the Dominican Republic on Sunday as forecasters predicted Tropical Storm Irene would strengthen as it neared the Caribbean islands.
Irene was nearing the U.S. Virgin Islands with top winds of 50 mph (85 kph) Sunday, the National Hurricane Center in Miami reported. At 5 p.m. ET, the storm was centered about 25 miles (40 kilometers) east of St. Croix and about 120 miles (195 kilometers) east-southeast from Puerto Rico, moving west-northwest at 17 mph (28 kph), forecasters said.
Tropical storm warnings covered the U.S. and British Virgin Islands, the northern coast of the Dominican Republic and Haiti.
The storm was expected to pass south of Puerto Rico overnight, strike the Dominican Republic on Monday and could reach the southeastern United States by Thursday, forecasters projected.
"Some strengthening is forecast during the next day or so, and Irene could become a hurricane on Monday," the hurricane center reported.
The hurricane center warned that Irene could dump heavy rain on the Dominican Republic and neighboring Haiti, where previous storms have caused deadly mudslides down deforested hillsides. The NHC said Haiti and the Dominican Republic could see up to 20 inches of rain in isolated areas, with six to 10 inches possible across the rest of Hispaniola.