Thunderstorms rolling across the Gulf Coast hampered the search Monday for four boaters still missing two days after a deadly squall overturned sailboats during a yearly race in Mobile Bay.

With two people already confirmed dead in the 57th annual Dauphin Island Regatta, crews used boats to search white-capped waters and asked volunteers to walk the shore in case anything washed up.

The Coast Guard provided a bit of good news: One person initially believed missing had been found safe at home following a check of people who had registered for the race.

But lightning popped and thunder rumbled as the hunt continued for four others in murky bay waters. On shore, about 20 relatives of the missing gathered at the state-run Dauphin Sea Lab to await word of loved ones.

"This very difficult, very difficult for all of them," said Michael Brown of the American Red Cross. "There is still hope. The Coast Guard has told them they are doing an active search and rescue."

The National Weather Service said heavy rains were possible through Monday night, and authorities asked volunteer searchers to remain on land to avoid any more casualties.

"We would like any of the good Samaritans to be off the water just for safety reasons," said Coast Guard Petty Officer 2nd Class Seth Johnson. "We appreciate their goodwill as a volunteer and if they'd like to, they can still search the shoreline."

The annual race, sponsored by Mobile-area yacht clubs on a rotating basis, begins in the middle of Mobile Bay. Sailboats ranging in size from small catamarans to single-hull craft capable of carrying a half-dozen people or more race southward through the shallow waters toward Dauphin Island, a barrier island on Alabama's coast.

More than 100 sailboats and as many as 200 people were participating in the 57th running of the race when the storm hit Saturday afternoon. Some skippers were able to lower sails and return safely to shore, but other boats capsized in fierce winds.

Gary Garner, commodore of the Fairhope Yacht Club, which organized the race, said members were "heartbroken" over the tragedy.

"We are helping and cooperating fully with the U.S. Coast Guard and other authorities in accounting for all of the sailors," he said in an emailed statement.

Weather Service meteorologist John Purdy said Sunday that the storm moved eastward through Louisiana and Mississippi quickly, prompting a severe thunderstorm watch at 1:36 p.m. Saturday and a warning less than an hour later.

The National Weather Service then issued a special marine warning around 3 p.m. for boaters on several waterways including Mobile Bay, warning of a line of thunderstorms producing gusty winds, high waves, dangerous lightning and heavy rains. The notice urged boaters to "seek safe harbor immediately."

"When storms are moving quickly as in this case, things will change very rapidly especially if you are on a boat in the open waters," Purdy said.