(CNN) -- Tropical Storm Rafael continued to churn Saturday evening through the Caribbean Sea, bringing heavy rain and powerful gusts to the Virgin Islands and threatening even more locales.
With sustained winds of 50 mph, Rafael could get even stronger in the coming days 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," forecasters at the National Hurricane Center said in a 8 p.m. advisory.
At that time, the tropical storm was centered about 25 miles west-southwest of St. Maarten and 85 miles east of St. Croix. It started to move faster over the course of the day Saturday, and by nighttime was advancing north at a 12 mph rate, the Miami-based weather agency said. Rafael should turn toward the north-northwest sometime Sunday.
A tropical storm warning is in effect for a number of Caribbean isles, including the U.S. and British Virgin Islands, St. Maarten, 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.
The storm's eye should pass over the northern Windward Islands and Virgin Islands sometime late Saturday.
Forecasters expect Rafael to dump between 3 to 5 inches of rain along its path, including 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," according to the hurricane center.
The storm may 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 on Saturday afternoon saved a 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 acknowledged were deteriorating conditions due to Rafael.