Tropical Storm Erika formed in the Atlantic early Tuesday, putting it on course for the Leeward Islands in the coming days, the National Hurricane Center said.
By the weekend, Erika is forecast to strengthen into a weak hurricane over the Bahamas.
However, at 2 p.m. Tuesday, the hurricane center said Erika had not changed strength.
Tropical storm watches are in place for Montserrat, Antigua, Barbuda, St. Kitts and Nevis, Anguilla, Saba and St. Eustatius. A tropical storm watch means that tropical storm conditions are possible in the watch area within 48 hours.
The system with its 45 mph winds was about 840 miles east of the Leewards on Tuesday morning.
Some strengthening is forecast during the next couple of days, the hurricane center said.