MIAMI BEACH, Fla — The Coast Guard battled time and currents Wednesday as its planes and ships searched for 38 people missing off the coast of Florida, four days after a suspected human smuggling boat capsized in a storm.

The accident killed at least one person and left a single known survivor.

Capt. Jo-Ann F. Burdian said the survivor told rescuers that the boat capsized Saturday evening shortly after sailing into a storm from the Bahamas. The Coast Guard was alerted Tuesday morning after the crew of a merchant vessel spotted the man sitting alone on the overturned hull of the 25-foot boat.

She said finding other migrants alive is urgent.

“With every moment that passes, it becomes much more dire and more unlikely” that survivors will be found, she told a news conference.

Crews searched around the clock, extrapolating from where the wreck was spotted about 40 miles (64 kilometers) off Fort Pierce. By Wednesday morning, crews on at least four ships and five aircraft scanned a vast area about the size of New Jersey, Burdian said. They planned to keep searching throughout the day and then reevaluate.

“We are using every piece of information we can to make sure we are exhausting our search efforts,” Burdian said. “But we can’t search forever.”

Wednesday’s forecast calls for rain and possible thunderstorms in the search area, with swells cresting at 2 to 3 feet (1 meter) and winds blowing at 12 to 15 mph (19 to 24 kph).

The rescued man said he was part of a group of 40 people who left the island of Bimini in the Bahamas in what the Coast Guard suspects was a human smuggling operation, Burdain said. The man said the boat capsized shortly thereafter, and no one aboard was wearing a life jacket, she added.

A small craft advisory had been issued as a severe cold front blew through the dangerous passage on Saturday and Sunday, with winds up to 23 mph (37 kph) and swells up to 9 feet (3 meters). Tommy Sewell, a local fishing guide, said there were high winds and fierce rain squalls from Sunday into Monday.

The survivor was brought to a hospital with symptoms of dehydration and sun exposure. Burdian would not provide any more details, saying he’s now in the custody of the Department of Homeland Security.

Bimini is a small island about 55 miles (90 kilometers) east of Miami and about 100 miles (160 kilometers) south of where the survivor was found. The capsized boat was apparently pushed north by the Gulf Stream, a warm, swift current that wraps around the Florida peninsula and flows north along the Atlantic Coast of the United States.

Migrants have long used the Bahamas as a steppingstone to reach Florida and the United States. They typically try to take advantage of breaks in the weather to make the crossing, but the vessels are often dangerously overloaded and prone to capsizing. There have been thousands of deaths over the years.

For the most part, these migrants are from Haiti and Cuba, but the Royal Bahamas Defense Force has reported apprehending migrants from other parts of the world, including from Colombia and Ecuador earlier this month.

The Coast Guard constantly patrols the waters around Haiti, the Dominican Republic, Cuba and the Bahamas. On Friday, its crews pulled 88 Haitians from an overloaded sail freighter west of Great Inagua, Bahamas.

Last July, the Coast Guard rescued 13 people after their boat capsized off of Key West as Tropical Storm Elsa approached. The survivors said they left Cuba with 22 people aboard. Nine went missing in the water.

In the fiscal year that ended Sept. 30, the Coast Guard said it apprehended 838 Cubans, 1,527 Haitians and 742 people from the Dominican Republic in the region that includes Florida and the Caribbean. The agency also apprehended migrants from other nations, but it did not provide a breakdown of the other nationalities.