MIAMI -- Forecasters say the fourth tropical storm of the Atlantic hurricane season is maintaining its strength as it moves toward the Windward Islands.

The U.S. National Hurricane Center said Sunday that Tropical Storm Dorian could intensify to near hurricane strength over the eastern Caribbean Sea by Tuesday.

As of 8 p.m. EDT Sunday, Dorian's centre was located about 335 miles (540 kilometres) east-southeast of Barbados and was moving west at 14 mph (23 kph). Maximum sustained winds are at 50 mph (85 kph).

A tropical storm warning is in effect for Barbados, St. Lucia, St. Vincent and the Grenadines. A tropical storm watch was issued for Grenada and Martinique.

Forecasters say Puerto Rico, the Dominican Republic, Haiti and the Virgin Islands should monitor Dorian's progress.