Tropical Storm Isaac is getting better organized as it approaches the Carribbean.
The storm's maximum sustained winds early Wednesday are near 45 mph (75 kph). The U.S. National Hurricane Center says Isaac is expected to strengthen and could become a hurricane by Thursday.
Tropical storm warnings are in effect for Puerto Rico, the U.S. and British Virgin Islands and a swath of islands across the Caribbean including Martinique, Dominica, Guadeloupe, St. Martin, St. Kitts, Nevis, Antigua, Barbuda, Montserrat, Anguilla, Saba, St. Eustatius, St. Maarten, Culebra and Vieques.
Isaac is centered about 280 miles (445 kilometers) east of Guadeloupe and is moving west near 18 mph (30 kph).
The storm's center is expected to move over the Leeward Islands on Wednesday evening.