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A hurricane watch has been issued for Puerto Rico, Vieques, Culebra and the U.S. Virgin Islands as Tropical Storm Isaac continued heading west Tuesday night, the National Hurricane Center in Miami said.
Isaac formed in the Atlantic Tuesday afternoon, becoming the ninth named storm of the 2012 hurricane season.
As of 11 p.m., Isaac had maximum sustained winds of 40 mph as it moved west at 18 mph about 390 miles east of Guadeloupe, according to the National Hurricane Center.
Tropical storm force winds extend outward up to 45 miles from the center of Isaac.
It became Tropical Depression 9 early Tuesday morning. An Air Force Reserve hurricane hunter aircraft determined that the depression had become a tropical storm later in the day.
NHC spokesman Dennis Feltgen said the storm could become a hurricane by late Wednesday or early Thursday, when the current track has it moving south of Puerto Rico.
Feltgen said South Floridians should keep an eye on the depression and be prepared just in case.
"We're not even in the cone yet, so there's no immediate concern," he said. "It wouldn't be bad idea for folks to start paying attention to this, especially later in the week, and make sure you've got your hurricane supplies."
Organizers for the Republican National Convention being held in Tampa next week are also watching the storm.
Tropical storm warnings were in effect for Martinique, Dominica, Guadeloupe and surrounding islands, St. Martin, St. Kitts, Nevis, Antigua, Barbuda, Montserrat, Anguilla, Saba, St. Eustatius, St. Maarten and the British Virgin Islands.
A tropical storm warning was also in effect for Puerto Rico, Vieques, Culebra and the U.S. Virgin Islands, the National Hurricane Center said.
The storm is expected to strengthen and continue moving west during the next couple of days. The center of Isaac should move through the Leeward Islands Wednesday evening and move over the northeastern Caribbean Sea on Thursday, forecasters said.
Up to eight inches of rain are possible over the northern Windward Islands and the Leeward Islands. A storm surge will raise water levels by up to 3 feet above normal tide levels in the northern Leeward Islands, Puerto Rico and the Virgin Islands, the National Hurricane Center said.