Port Fourchon, La. — The Coast Guard searched for 12 people missing off the coast of Louisiana on Wednesday after finding one person dead and pulling six survivors from rough seas when their commercial vessel capsized in hurricane-force winds.

Coast Guard Capt. Will Watson said winds were 80 to 90 mph and seas were 7 to 9 feet when the Seacor Power lift vessel overturned.

“That’s challenging under any circumstance,” Watson said. “We don’t know the degree to which that contributed to what happened, but we do know those are challenging conditions to be out in the maritime environment.”

The bulky vessel with three long legs it can lower to the sea floor to become an offshore platform flipped over Tuesday afternoon miles south of Port Fourchon, a major base for the U.S. oil and gas industry.

One worker was found dead on the surface of the water, Watson said at a news conference Wednesday. Asked about the prospects of the missing crew, he said: “We are hopeful. We can’t do this work if you’re not optimistic, if you’re not hopeful.”

Lafourche Parish President Archie Chaisson III said time is critical in the rescue effort because more rough weather was in the forecast.

“The hope is that we can bring the other 12 home alive,” Chaisson said.

Marion Cuyler, the fiancée of crane operator Chaz Morales, was waiting with wives and family members of other missing workers at a fire station near a landing site where helicopters were coming and going. She said she talked to her fiancée before he left Tuesday.

“He said that they were jacking down and they were about to head out, and I’m like, ‘The weather’s too bad. You need to come home.’ And he’s like, ‘I wish I could.’”

The relationship of all on board to ship owner Seacor Marine was not immediately clear. The ship, which can work in up to 195 feet of water, can carry a crew of 12, two “special personnel” and 36 passengers, according to the company website. An employee who answered the phone Wednesday morning at Houston-based Seacor Marine said he had no immediate information he could share.

While noting the harsh weather conditions, Watson said its role in the capsizing was under investigation. The vessel left Port Fourchon at 1:30 p.m. Tuesday, bound for Main Pass off the southeast Louisiana coast, he said.

“We did have some weather reports yesterday that there would be some challenging weather. But this level of weather was not necessarily anticipated,” he said.

The National Weather Service in New Orleans issued a special marine warning before 4 p.m. Tuesday that predicted steep waves and winds greater than 58 mph.

The Coast Guard received a distress message from a good Samaritan at 4:30 p.m. and issued an urgent marine broadcast that prompted multiple private vessels in the area to respond, saving four people, the agency said. Coast Guard crews rescued another two people.

At one point, video showed the massive ship — 129 feet long at its beam — with one leg pointed awkwardly skyward as rescuers searched the heaving water.

Although the Coast Guard said the lift boat capsized during a microburst, a National Weather Service meteorologist said the system was more like an offshore derecho.

“This was not a microburst — just a broad straight-line wind event that swept over a huge area,” Phil Grigsby said.

He said the weather service’s nearest official gauge, at Grand Isle, showed about 30 minutes of 75 mph winds, followed by hours of winds over 50 mph.

The initial storm system was followed by a low-pressure system called a wake low, which amplified the winds and made them last longer, Grigsby said. “It was the strongest wake low I’ve seen in almost 18 years here,” he said.

Capt. Aaron Callais said the bad weather started with small, quickly dissipating waterspouts that buffeted his father’s shrimp boat, the Ramblin’ Cajun.

“There was nothing we could do. One minute we were facing north, the next south, then east and west,” he said. “Things were flying in the cabin.’

Callais posted video on Facebook of wind battering the boat as he talked to friends and family, including his dad, “letting him know the situation, that it wasn’t looking good. We didn’t know if we were going to make it out.”