Tammy could be a hurricane when it tracks through the northeast Caribbean islands later this week.
Tropical storm watches have been issued for Barbados, Dominica, Martinique and Guadeloupe.
A Tropical Storm Watch means that tropical storm conditions are possible within the watch area, generally within 48 hours.
The National Hurricane Center said additional watches and warnings will likely be required later tonight or on Thursday.
At 1100 PM AST (0300 UTC), the center of Tropical Storm Tammy was located near latitude 13.0 North, longitude 53.1 West. Tammy is moving toward the west near 17 mph (28 km/h). A westward motion with an additional slow down is expected on Thursday. A turn toward the west-northwest is forecast by Thursday night, followed by a turn
toward the northwest Friday night or Saturday. On the forecast track, the center of Tammy will move near or over the Leeward Islands Friday and Saturday.
Maximum sustained winds are near 40 mph (65 km/h) with higher gusts.
Additional strengthening is forecast during the next couple of days and Tammy could be near hurricane intensity by the end of the weekend.
Tropical-storm-force winds extend outward up to 140 miles (220 km) from the center.
The estimated minimum central pressure is 1006 mb (29.71 inches).
WIND: Tropical storm conditions are possible within the watch area beginning on Friday.
RAINFALL: Through Saturday night, Tammy is expected to produce storm total rainfall of 3 to 6 inches, with maximum amounts of 10 inches, across portions of the northern Windward into the Leeward Islands. Rainfall totals of 1 to 2 inches with maximum amounts of 4 inches are expected for the British and U.S. Virgin Islands into eastern Puerto Rico. These rains may produce isolated flash and urban flooding, along with isolated mudslides in areas of higher terrain.
SURF: Swells generated by Tammy will begin affecting portions of the Lesser Antilles on Thursday. These swells are likely to cause life-threatening surf and rip current conditions.