BRIDGETOWN (Reuters) – Residents of Barbados and other Caribbean islands braced for heavy rains as tropical storm Dorian churned west-northwest, with officials cautioning that it could approach hurricane strength on Tuesday.

Puerto Rico Governor Wanda Vázquez Garced declared a state of emergency for the U.S. territory late on Monday in anticipation of the storm, the government said on Twitter.

There will be about 360 shelters open across the island, the governor announced.

Dorian is expected to pass on the southwest side of Puerto Rico as a hurricane on Wednesday night, the National Hurricane Center said in an advisory.

Barbados, which is closest to the storm’s path, was hit by strong winds and intermittent showers, with periodic jolts of thunder and lightning, on Monday evening.

The Barbados Meteorological Services warned residents to exercise caution, saying wind speeds have climbed over the past six hours and will strengthen further overnight and into Tuesday morning.

A tropical storm watch is in effect for Puerto Rico, and the island of Santa Lucia is on hurricane watch.

Dorian tracked near the Windward Islands on Monday evening and is expected to reach the eastern Caribbean later on Tuesday, the U.S. National Hurricane Center said in a report.

By Tuesday morning, the storm was located about 30 miles (48 km) southeast of St. Lucia, blowing maximum sustained winds of 50 miles per hour, according to the NHC.

(Reporting by Robert Edison Sandiford; additional reporting by Rich McKay; Editing by Michael Perry and Ed Osmond)