MIAMI -

Tropical Storm Isaac continues to move west Wednesday morning. The National Hurricane Center upgraded Tropical Depression 9 to a tropical storm on Tuesday evening.

In the 5 a.m. advisory, Isaac had sustained winds of 45 mph and was moving west at 18 mph. The center was about 280 miles east of Guadeloupe.

A hurricane watch is in effect for Puerto Rico, Vieques, Culebra and the U.S. Virgin Islands.

Tropical storm warnings are in effect for Martinique Guadeloupe and the surrounding islands, St. Martin, St. Kitts, Nevis, Antigua, Barbuda, Montserrat, Anguilla Saba, St. Eustatius, St. Maarten, the British Virgin Islands, and parts of Puerto Rico, Vieques, Culebra and the U.S. Virgin Islands.

A tropical storm watch is in effect for the north coast of the Dominican Republic from the Haiti-Dominican Republic northern border eastward to north of Isla Saona.

Long range models show the storm will move into the Caribbean on Thursday morning, before heading for the southern side of Hispaniola and Cuba. The storm could potentially turn north and threaten South Florida early next week. Additional strengthening is forecast during the next 48 hours.

As Isaac approaches South Florida, read what Hurricane Specialist Max Mayfield suggests residents do to prepare.