SAN JUAN, Puerto Rico -- The eastern Caribbean is bracing for heavy winds and rain after Tropical Storm Don formed Monday in the Atlantic Ocean.

A tropical storm warning was in effect for Grenada, while a tropical storm watch was in effect for the nearby islands of Barbados, St. Lucia and St. Vincent and the Grenadines.

The storm had maximum sustained winds of 40 mph (65 kph) and was moving west at 17 mph (28 mph) on Monday afternoon, according to the National Hurricane Center. It was located about 485 miles (780 kilometres) east-southeast of Barbados and 595 miles (958 kilometres) east of Trinidad, forecasters said.

The storm's centre is expected to move through the Windward Islands on Tuesday night and drop between two to four inches (five to 10 centimetres) of rain through Wednesday morning.

An Air Force Reserve crew found the storm small and well-defined but not particularly well-organized. Forecasters said Don is expected to dissipate within 72 hours.