The governments of Martinique and St Lucia have placed the islands under a tropical storm watch ahead of the passage of Tropical Storm Bret.
They join Barbados and Dominica, who were placed under a tropical storm watch.
Bret is expected to move across portions of the Lesser Antilles late on Thursday and then move across the eastern Caribbean Sea on Friday.
The US National Hurricane Centre (NHC) said Bret’s winds have increased to near 60 mph (95 km/h).
“Some additional increase in strength is possible before Bret reaches the Caribbean Sea,” NHC said.
Forecasters expect Bret to dump a significant amount of rainfall across portions of the Lesser Antilles from Guadeloupe to Grenada and Barbados.
NHC said the heavy rainfall could lead to flash flooding, especially across areas of higher terrain.
