Hurricane watches are active throughout the Caribbean, and the U.S. Navy has put forces at Guantanamo on alert. Weather Channel meteorologist Jim Cantore reports.

As Tropical Storm Isaac makes its way over the Caribbean on Wednesday, forecasters expect it to turn into a hurricane later this week, sparking worries that it could threaten next week's Republican National Convention in Florida.

The storm is getting better organized as it moves west at 21 mph, with maximum sustained winds of 45 mph as of Wednesday morning. Forecasters predict Issac could turn into a hurricane by Friday.

Related: Click here to track Isaac's path

Schools and government offices are closed across much of the Caribbean Wednesday as Isaac was positioned 140 miles east of the French Caribbean island of Guadeloupe.

In addition to much of the Caribbean, tropical storm warnings are also in effect for Puerto Rico and the U.S. and British Virgin Islands. Puerto Rico, Vieques, Culebra, the U.S. and British Virgin Islands and the south coast of the Dominican Republic are all under a hurricane watch.

Dominica Prime Minister Roosevelt Skerrit encouraged people to stay home from work on Wednesday, according to the AP.

"I want us all to be safe," he said. "I don't want lives to be lost. I have listened to the advice of the experts and so I am asking all to stay indoors."

TODAY's Al Roker tracks Tropical Storm Isaac as it swirls in the Atlantic and discusses whether or not the Republican National Convention in Tampa, Fla., will be plagued with heavy rains and high winds.

Puerto Rico is also bracing for the worst: Gov. Luis Fortuno activated the National Guard and declared a state of emergency, the AP reported.

By Wednesday evening, the storm's center is expected to be over the Leeward Islands, and it will move toward the Dominican Republic, Haiti and Cuba as a hurricane later this week, according to the AP.

AFP PHOTO / NASA GSFC GOES PROJECT Tropical Storm Isaac strengthened on Wednesday and looked set to become a hurricane as it churned through the Caribbean.

National Hurricane Center computer models indicate that Isaac could move northwest and eventually reach Florida by Monday morning — the same day as the start of the Republican National Convention in Tampa.

Next week's GOP convention is expected to attract thousands of Republicans to nominate Mitt Romney for president and Paul Ryan for vice president. While it's too soon to tell whether Isaac will hit Tampa directly, senior hurricane specialist Lixion Avila, with the National Hurricane Center, told Reuters that Tampa is not out of harm's way.

"With the convention or without the convention, I can tell you this is August 22, hurricane season, and normally anywhere in Florida or the Gulf of Mexico we should monitor any system that forms," Avila said.

Sept. 1: On the first day of its convention, the GOP tries to prove it is capable of responding to a natural disaster. According to NBC's Andrea Mitchell, the party is confident they can get back to normal after Gustav.

The Weather Channel's Bryan Norcross wrote a warning post on his Facebook page Wednesday: "Okay Florida ... it's time to wake up. Isaac is getting organized and the odds are increasing that it's going to be a problem ... a big enough problem that preparation is likely to be required."

Both Tampa and GOP officials say there are contingency plans in case the storm hits. FEMA has water and meals ready in the U.S. Virgin Islands.

In 2008, Hurricane Gustav churning toward New Orleans disrupted the Republican convention that was getting under way in Minneapolis. President George W. Bush Vice President Dick Cheney and Sen. Joe Lieberman canceled Sept. 1 speeches. Bush delivered a speech by satellite the next day. Aides to Sen. John McCain, the party’s presidential nominee, chartered a jet so Gulf Coast delegates could return home, according to media reports at the time. The storm largely spared New Orleans, battered by Hurricane Katrina in 2005, but came ashore as a Category 2 hurricane and spawned damaging tornadoes.

Elsewhere, forecasters are also keeping an eye on Tropical Depression 10, which has formed over the eastern tropical Atlantic.

The Associated Press and Reuters contributed to this report.

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