Hurricane Gustav is moving across the Caribbean toward southwestern Haiti, where it is expected to make landfall later Tuesday.
U.S. forecasters say the storm's winds strengthened on Tuesday morning to nearly 150 kilometers per hour.
Gustav is expected to produce up to 38 centimeters of rain in some areas, possibly causing dangerous flash floods and mudslides.
The National Hurricane Center in Miami upgraded Gustav to a hurricane early Tuesday.
A hurricane warning is in effect for parts of Haiti and the Dominican Republic, where Tropical Storm Fay claimed an estimated 50 lives less than two weeks ago. Fay has weakened a tropical depression, causing heavy rains in the eastern United States.
Forecasters expect Hurricane Gustav to pass just south or east of Cuba on Wednesday.
Cuba and Jamaica have issued hurricane watches.