Puerto Rico ? Tropical Storm Chris strengthened Tuesday as it entered the eastern edge of the Caribbean, prompting a run on groceries and gas as people prepared for the third named storm of the Atlantic hurricane season.

The storm had top winds of nearly 45 mph as it passed over the Leeward Islands, and was expected to gather strength as it approached the U.S. and British Virgin Islands and Puerto Rico, according to the U.S. National Hurricane Center in Miami. Forecasters doubted it would become a hurricane.

Long-range forecasts put the storm anywhere from south of Cuba to Florida by late in the weekend.

Late on Tuesday, Chris was about 300 miles southeast of San Juan, Puerto Rico, moving northwest at 10 mph with sustained winds of 60 mph. The storm was expected to douse the northern Leeward Islands and Puerto Rico with up to 8 inches of rain by this morning.