Tropical Storm Isaac strengthened on Wednesday and looked set to become a hurricane as it churned through the Caribbean on a path that could have it hit Florida during next week's Republican convention.

The storm, packing gusts of up to 45 miles (75 kilometers) per hour, was expected to intensify over the next two days and "could become a hurricane by Thursday," the US National Hurricane Center said in its 1200 GMT bulletin.

A tropical storm warning was in effect throughout the Lesser Antilles, including Martinique, Dominica and Guadeloupe, and a hurricane watch has been issued for Puerto Rico, the US and British Virgin Islands.

The NHC's five-day forecast has the storm possibly striking Florida as early as Monday, when the US Republican National Convention opens in Tampa.

But meteorologists have cautioned that it is too early to accurately predict the storm's path and said it is unlikely to disrupt the convention.

Thousands of Republicans, including party leaders and rising stars, will descend on Tampa next week for four days of speeches and pageantry in which former Massachusetts governor Mitt Romney will be formally nominated to challenge President Barack Obama in the November 6 election.