Tropical Storm Isaac is barreling toward Puerto Rico and Cuba, and threatens to upend the Republican National Convention in Tampa if it continues north.

Even during an average summer thunderstorm in this area, major roads can flood. 

When a tropical storm raked the Tampa Bay area a couple of months ago, thousands of homes and businesses lost power, tornadoes spun off and streets and bridges were closed. It's still too early to say where Isaac will end up, but officials are closely watching the storm and say they're ready to make any decisions, if needed, about evacuations or cancellations as 70,000 delegates, journalists and protesters descend on the city.

"Public safety will always trump politics," Tampa Mayor Bob Buckhorn said. "And so my job, and our job, if we move into that mode, is to make sure we get people out of harm's way. I don't care whether they're anarchists or they're delegates."

The current forecast has Isaac strengthening into a hurricane Thursday night and heading toward South Florida, arriving around Monday, the opening day of the convention and nearly a week of parties, speeches and other events culminating with the coronation of Mitt Romney.

The storm was still hundreds of miles from the tip of Florida on Wednesday, with maximum sustained winds of 45 mph. Forecasters warned there was still a great deal of uncertainty with Isaac, and it could miss the state altogether.

"The storm is so far away at this point, the cone of error from this point out is tremendous," said Florida Emergency Management Director Bryan Koon, who has been in constant contact with RNC officials about the storm threat.

Leaders across much of the Caribbean closed schools and government offices on Wednesday as Isaac swept toward the region, and the U.S. military postponed hearings for Sept. 11 prisoners ahead of the storm. 

The storm was 75 miles (120 kilometers) east-northeast of Dominica early Wednesday afternoon, where the island's Prime Minister Roosevelt Skerrit urged people to stay home from work on Wednesday.

In Puerto Rico, Gov. Luis Fortuno declared a state of emergency and activated the National Guard. He also canceled classes and closed government agencies on Wednesday. 

Federal officials closed the popular San Felipe del Morro castle in Old San Juan. The storm was expected to pass just south of Puerto Rico on Thursday.

The U.S. Coast Guard closed all ports in Puerto Rico and the U.S. Virgin Islands to incoming commercial ships and warned that all commercial vessels bigger than 200 gross tons must leave or obtain permission to remain in port.

Based on reporting by the Associated Press.

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