MIAMI
08/21/2012 08:05 am ET Updated Oct 21, 2012

Tropical Depression 9 Expected To Become Tropical Storm Isaac; Could Head For South Florida

Keep an eye on this one, Miami!

A tropical depression headed for the Caribbean is expected to become a tropical storm later Tuesday, and advance forecasts by the National Hurricane Center show a possibility it could head for South Florida early next week as Hurricane Isaac.

Tropical Depression 9 is currently moving west toward the Lesser Antilles at 20 miles per hour as it churns 645 miles east of Guadaloupe. NHC officials say it could become a hurricane early Thursday morning near Puerto Rico, after which the "cone of uncertainty" suggests a turn to the north that could send Isaac over Haiti and Cuba toward South Florida.

(Also of concern: whether or not Isaac could disrupt the Republican National Convention in Tampa.)

Forecasters say environmental conditions over the next few days are "quite favorable" for the storm to intensify, though it would likely level off after hitting the mountains of Haiti and Cuba.

TD 9 currently has maximum sustained winds of 35 mph. An Air Force reserve reconnaissance plane is scheduled to check out the system Tuesday afternoon.

Meanwhile, tropical storm warnings -- issued when such conditions are expected within 36 hours -- are in place for Dominica, Guadeloupe, Desirade, Les Saintes, Marie Galante, St. Martin, St. Kitts, Nevis, Antigua, Montserrat and Barbuda.

Tropical storm watches, which warn storm conditions may be possible in 48 hours, have been issued for Puerto Rico, the U.S. Virgin Islands, Vieques, Culbera, Saba, St. Eustatius, St. Maarten and the British Virgin Islands.

UPDATE, 6 p.m.: Tropical Storm Isaac has formed, according to the National Hurricane Service. Reports from a hurricane hunter aircraft indicated the system has maximum sustained winds of 40 miles per hour; Isaac is expected to continue to strengthen over the next 48 hours.

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