Tropical Storm Fred formed in the Caribbean on Tuesday night, strengthening from a disturbance as it lashed Puerto Rico with gusty winds and heavy rain, forecasters said.
Parts of the island, as well as the Dominican Republic and the Virgin Islands, could get up to 4 inches of rain, with isolated maximums of 6 inches, the National Hurricane Center said.
Fred is the sixth named storm of the Atlantic hurricane season, which runs from June 1 through Nov. 30.
The storm was about 50 miles southeast of Santo Domingo, Dominican Republic, at 8 a.m. Wednesday. Fred had maximum sustained winds of 40 mph and was moving west at 16 mph.
Officials in Puerto Rico warned people to take the storm seriously. The National Hurricane Center said heavy rain was spreading across the island.
"Do not wait until the last minute to mobilize," said Nino Correa, Puerto Rico's emergency management commissioner. "We don't want to have fatalities."
Tropical storm warnings and watches were in effect for Puerto Rico, the U.S. Virgin Islands and Hispaniola. None had been issued for the continental U.S. yet.
Forecast tracks estimate that the storm will approach Florida this weekend, with a risk of rain and wind affecting the Keys starting Friday, forecasters said. Fred is forecast to be a 45 mph tropical storm as it moves past South Florida on Saturday morning.
"However, it is too soon to determine the exact timing, location and magnitude of any potential impacts" for the state, the hurricane center said in a discussion on its website.
The National Oceanic and Atmospheric Administration has predicted a busier-than-average Atlantic hurricane season. It said last week that conditions remain favorable, predicting 15 to 21 named storms, with seven to 10 hurricanes, in an update Aug. 4.
Last season was a record-breaking one, with 30 named storms, 12 of which made landfall. They included two hurricanes, Laura and Delta, that struck southwest Louisiana within six weeks of each other.