Tropical Storm Erin has begun to strengthen and is expected to reach major hurricane intensity this weekend as it tracks just north of the Caribbean islands, where it could bring rain, gusty winds and high surf.

The storm is expected to remain over open waters and move north-northeast of islands including Antigua and Barbuda, the U.S. and British Virgin Islands and Puerto Rico, according to the National Hurricane Center in Miami.

The storm is forecast to strengthen into a major Category 3 hurricane and turn north, but impacts on the U.S. east coast are likely.