Sal Aurelino told TV's News12 Long Island that he was taking the Candi One home when he saw two lightning bolts, and "a wave got us."
"It turned the boat around," he said, his voice cracking. "It just turned the boat. I didn't see it. It was dark. I didn't see it.
Aurelino's nephew David, 12, and two girls, 11-year-old Harley Treanor and 8-year-old Victoria Gaines, were trapped in the cabin and died. The 24 other passengers survived after the boat flipped in the waters near Oyster Bay.
"The next thing I know, we're turning, and we just kept turning, and everybody was in the water. It was chaos," Aurelino said.
Nassau County Detective Lt. John Azzata said it wasn't clear what caused the accident, but it could have been the weather or overcrowding aboard the 34-foot yacht, which was carrying 27 people in all. It's also possible the yacht was swamped by the wake of another vessel because the area was crowded with boaters watching the fireworks, Azzata said.
He said alcohol was not believed to be a factor.
The Silverton yacht was made in 1984 but was "a very recent purchase," he said.
Azzata said the boat should have had a life jacket for each person on board. But authorities could not determine if the boat had 27 life jackets because the vessel remained under water. Police said it capsized and then drifted a bit before it sank in about 60 feet of water.
The first body was found shortly after the 911 call came in around 10 p.m. Wednesday, and the two others were found later inside the yacht, said Nassau County Deputy Inspector Kenneth Lack. He said the operation took a long time because "at night in an area like this, it is very dangerous."
Many boaters in the area helped with the rescue effort.
"It was a lot of people in the water," Lack said. "Most people were taken aboard other crafts very quickly."
At least two of the children were believed related.
Mike Treanor, who was related to some of the victims, answered the door to a family home on a suburban, tree-lined street. "It's a family tragedy," he said, adding there would be no further comment.
Police said those aboard were watching fireworks at Cove Neck Shore. The National Weather Service said a thunderstorm moved through the area around 10:30 p.m., and winds never exceeded 10 to 15 mph.
A boater told Newsday he saw the yacht turn right and then tip over after it was hit by a wake. "It was like in slow motion," said Sammy Balasso of Oyster Bay. "All of a sudden, a lot of bodies were in the water."
His nephew, 15-year-old Frankie Barbone, said the waves almost came up over the yacht.
Balasso said he put the spotlight of his 38-foot speedboat on the Silverton and then threw all the life jackets he had with him into the water. He said he rescued 20 people, who were later taken to the shore in police boats.
"Everybody was panicking," Balasso said. "People were saying things like `Why?"'