(CNN) -- Tropical Storm Rafael unleashed heavy rain and powerful gusts to the Virgin Islands and threatened more areas in the Caribbean Sea late Saturday night.
With sustained winds of 50 mph, Rafael could get even stronger as it bears down on several islands popular with tourists.
"Some strengthening is forecast during the next 48 hours, and Rafael could become a hurricane by late Monday," the National Hurricane Center in Miami said at 11 p.m. Saturday.
At that time, the tropical storm was centered about 40 miles west-northwest of St. Marten and 95 miles east of St. Croix. Rafael was moving north at 14 mph.
A tropical storm warning is in effect for a number of Caribbean isles, including the U.S. and British Virgin Islands, St. Marten, Anguilla, Antigua, Barbuda, St. Kitts and Guadeloupe. Dousing rains and steady winds in excess of 39 mph are expected in 12 to 24 hours in these places, according to the hurricane center. Puerto Rico is under a tropical storm watch, meaning such conditions are possible.
Forecasters expect Rafael to dump between 3 to 5 inches of rain over the Lesser Antilles and Virgin Islands, with some pockets getting as much as 10 inches.
"These rains could cause life-threatening flash floods and mudslides, especially in areas of mountainous terrain," the hurricane center said.
The storm could impact rescue efforts for two men and one woman whose small aircraft crashed Saturday morning about six nautical miles (7 miles) south of St. Thomas in the U.S. Virgin Islands, Coast Guard spokesman Ricardo Castrodad said. They were aboard a twin-engine Piper PA-23 that left St. Croix destined for St. Thomas, according to Federal Aviation Administration spokeswoman Kathleen Bergen.
Rescue crews from the Coast Guard and U.S. Virgin Islands Department of Natural Resources saved one female passenger, Valerie Jackson, who told them three others were still unaccounted for.
A Coast Guard cutter ship, two helicopters and a fixed-wing aircraft have been dispatched from Puerto Rico for the search, Castrodad said. The effort continued Saturday night despite what the Coast Guard spokesman said were deteriorating conditions due to Rafael.
CNN's Chandler Friedman contributed to this report.