Rafael is forecast to strengthen Tuesday and will likely become a hurricane over the next 24 hours as it batters the western Caribbean on the first leg of an uncertain journey toward the US Gulf Coast.

MIAMI - The lower and middle Florida Keys are now under a tropical storm warning as Tropical Storm Rafael is forecast to grow steadily as it churns past Jamaica's west coast on a path for Cuba, where it's expected to arrive later in the week as a hurricane.

Tropical Storm Rafael is forecast to become a hurricane in the northwestern Caribbean near the Cayman Islands before making landfall in Cuba.