A long-period northwest swell started filling in Thursday afternoon, drawing big-wave surfers out to the North Shore’s peaks.

With winter on its way, sizable surf has already hit Oahu, but Thursday saw it grow orderly and clean — a good training day for experienced surfers. And today is supposed to be “epic,” according to the surf forecasting website Surfline. The National Weather Service issued a high-surf warning for Thursday and an advisory for today.

A half-dozen men examined their Jet Skis and tow-boards at Haleiwa Boat Harbor on Thursday afternoon. Leading them was Ron Barron, 67, who expected to see faces of 20 to 25 feet breaking over the reefs outside Puaena Point. “That’s warning levels, and that means we’re able to go out,” Barron said.

He considered it a good training day for 15-year-old Peter Nagel, who stood nearby. Nagel planned to be “just surfing right now,” until he learned to drive a Jet Ski. “We’re teaching him how to drive,” Barron said.

Up the road at Waimea Bay, professional big-wave surfers Billy Kemper and Mason Barnes were squeezing into their impact-absorbent wetsuits.

“This is kinda the first time Waimea broke this season,” Barnes, 28, said. “Nothing crazy, but any time Waimea breaks it’s a special time no matter what, whether it’s 40 feet or 10 feet,” he said, waxing up a 9-foot purple Pyzel Padillac.

On the tailgate of his truck, Kemper worked CO2 canisters into an inflatable vest. “I don’t even consider this a Waimea day,” Kemper said. “‘Pinballs’ is what we call Waimea when it’s under 15 feet,” he said.

Kemper is a decorated big-wave surfer who most recently won the 2022 Red Bull Big Wave Award for the Biggest Paddle In, for a barrel he surfed at Jaws. But on Thursday he was testing a new wetsuit and fins. “The purpose of this session is for me to fall,” he said, threading the pull cables from his inflatable vest out of his suit. The fins “are based around Jaws,” he said.

“They’re not allowed to be ridden at Nazare,” he said, teasing Barnes, who had recently travelled to Portugal to surf Nazare, one of the world’s most enormous breaks.

“Come on,” said Barnes. He won the 2022 Red Bull Big Wave Award for the Biggest Tow wave for a monster he caught at Nazare in March.

Kemper hefted his 8-foot-4-inch Pyzel Padillac, and the duo walked down to the beach and paddled out.

Meanwhile, less knowledgeable people hoped to join in the life aquatic, tempted by Waimea’s heaving shorebreak.

A loudspeaker from the lifeguard tower crackled to life: “OK, guys, if you do not have fins and a lot of years of experience at this beach, we do not want you in the water. That’s you two guys right there in the shorebreak,” the lifeguard, hidden from view, said. “You guys are done. Please bring it back up on the beach. I want to make sure everybody makes it home tonight,” he said.

The two men in the shorebreak crawled up the steep beach-face. A man wearing fins and two young men paddling shortboards continued to throw themselves into unmakable waves.

“It’s all fun until it isn’t,” the lifeguard told the crowd of dozens of shorebreak watchers.

By the end of the day, the mounting swell had drawn about 1,000 people to Waimea Bay, lifeguard Joey Cadiz estimated. He rescued two from the shorebreak in the morning, he said.

“People come here on vacation and feel very entitled to doing what they intended to do, so we try to educate them,” Cadiz, 32, said. “Hopefully, the wave itself is a good enough warning, but oftentimes people are oblivious to it,” he said.

The rising swell can take people by surprise. “It jumped up from 6 feet this morning to 20 feet now. It happens really quickly,” Cadiz said.

After the sun had set, the sky began to turn gray, and the lifeguards prepared to sign off. Dozens of people still watched from the berm. “Good luck, everybody,” a lifeguard on the loudspeaker said. “May God bless you.”