( 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 .
NEW : The center of Rafael passes St. Martin and is heading north . The tropical storm could become a hurricane by Friday . Efforts to find three passengers on a downed plane continue despite the weather . Tropical storm warnings are in effect for many Caribbean islands .