A state of emergency has been declared in Puerto Rico.
The island is under a tropical storm warning and hurricane watch.
Forecasters say Dorian is expected to hit the island Wednesday as a tropical storm but could reach hurricane strength between now and then.
Puerto Ricans are scrambling to stock up on supplies before the storm hits.
Other parts of the Caribbean are also making preparations.
In Barbados, anxiety over the storm has motorists lined up bumper-to-bumper to fill up on gas.
And in Florida, FEMA activated two federal task forces: one headed to Puerto Rico and another to Saint Croix to assist wherever they are needed.