By the end of the week the storm is expected to be south of Jamaica, where the Caribbean is still warm enough to feed a major hurricane, said hurricane specialist Stacy Stewart.
However, the storm, which formed Sunday, is not expected to threaten the United States.
At 10 p.m. EST, the storm was centered about 275 miles south of San Juan, Puerto Rico. Its maximum sustained wind speed was about 35 mph and was it was moving west-northwest at about 9 mph.
Dangerous rip currents and up to 12 inches of rain were possible across the Windward Islands, the Leeward Islands, Puerto Rico and the Virgin Islands, Stewart said.
If the system becomes a tropical storm — which would happen if its maximum sustained wind reaches 39 mph — it would become the 24th named storm of the Atlantic hurricane season, extending this year's record. The previous record of 21 named storms had stood since 1933.
Letters from the Greek alphabet are being used to name storms because the list of 21 storm names was exhausted.