Tropical storm watches were issued early on Tuesday as Erika, the fifth named storm of the Atlantic hurricane season, moved toward the Eastern Caribbean, the U.S. National Hurricane Center said.
The tropical storm is likely to strengthen slowly and could reach hurricane status over the Bahamas by the weekend, though the Miami-based government forecaster said there was "considerable uncertainty" over its future intensity.
Erika formed on Monday and could threaten the U.S. East Coast early next week if it manages to fight off dry air and wind shear, which are unfavorable for storm strengthening, according to Jeff Masters of the private forecaster Weather Underground.
The storm was located about 605 miles (975 km) east of the island of Antigua with maximum sustained winds of 40 miles per hour (64 kph). It was expected to near land by Wednesday night, the hurricane center said in a Tuesday afternoon advisory.
Tropical storm watches were issued for the islands of Guadeloupe, St. Martin/St Maarten, St. Barthelemy, Montserrat, Antigua and Barbuda, St. Kitts and Nevis, Anguilla, Saba and St. Eustatius.
The government's annual forecast predicted a quieter-than-normal 2015 Atlantic hurricane season, with six to 10 named storms and up to four reaching hurricane status of 74 mph (119 kph).
Last week the season's first hurricane, Danny, while still far out at sea reached Category 3 on the Saffir-Simpson scale of intensity, with winds of between 111 and 129 mph (178-208 kph), before rapidly dissipating as it reached the Caribbean islands.
The Saffir-Simpson scale measures potential property damage from a storm, with hurricanes reaching Category 3 and higher considered "major" hurricanes with a potential for significant loss of life and damage.
Among the factors in this year's predicted weaker hurricane season is the El Niño weather phenomenon, the warming of Pacific waters that affects wind circulation patterns and makes the formation of hurricanes in the Atlantic-Caribbean basin less likely.