* Storm warnings issued for eastern Caribbean islands
* Isaac expected to strengthen into hurricane near Puerto Rico
* Storm's track may include Florida, where Republican convention to be held
By Kevin Gray
MIAMI, Aug 21 (Reuters) - Tropical Storm Isaac formed in the Atlantic Ocean on Tuesday and was expected to strengthen into a hurricane later this week as it moves on projected path across most of the Caribbean, the U.S. National Hurricane Center said.
Isaac was centered 500 miles (805 km) east of the island of Guadeloupe. The storm had top winds of 40 miles per hour (64 km per hour) and is forecast to become a hurricane by Thursday as it approaches Puerto Rico.
Computer forecast models show the storm moving as a hurricane across parts of Puerto Rico and then the Dominican Republic, Haiti, Jamaica and a large swath of Cuba.
It was too early to know whether Isaac would threaten energy interests clustered in the Gulf of Mexico. Meteorologists at Weather Insight, a private forecasting company and a unit of Thomson Reuters, gave the storm a 60 percent chance of entering the Gulf as a hurricane.
The storm is expected to move west across the Caribbean this week and veer northwest, potentially putting Florida in its path.
Robbie Berg, a hurricane specialist at the hurricane center, said the storm's path after its projected passing over Cuba on Sunday was unclear.
"Right now, it's watch-and-see and monitor," he said.
The center of Isaac, the ninth named storm of the Atlantic-Caribbean hurricane season, is expected to move through the central Lesser Antilles on Wednesday evening and emerge over the eastern Caribbean Sea on Thursday, the center said.
Tropical storm warnings were issued for the Caribbean islands of Martinique, Dominica, Guadeloupe, Antigua and parts of Curacao.
A tropical storm watch was also in effect for the British Virgin Islands, Puerto Rico and the U.S. Virgin Islands.
Hurricane expert Jeff Masters of private forecaster Weather Underground said most models appeared to agree on the storm's path through the Caribbean over the next three days.
The storm, which began as Tropical Depression Nine before being upgraded to a tropical storm, will likely be followed closely by many in Florida, where the Republican National Convention will be held Aug. 27-30 in Tampa.
Masters said the chances of a hurricane forcing an evacuation during the convention were "probably near 2 percent."
"It would take 'perfect storm' sort of conditions to all fall in place to bring Tropical Depression Nine to the doorstep of Tampa as a hurricane during the convention, but that is one of the possibilities the models have been suggesting could happen," he said.