Greg Long had it on good authority that a wave bigger than any hed ridden at Mexico’s Islas Todos Santos could arrive between 10:20 and 10:40 A.M. on January 6, 2023. The 40-year-old had been chasing swells down to the islands in northern Baja since he was a teenager in the 1990s, planning his trips using the crude surf forecasting available at the time—a fax with a three-day outlook from a nascent company called Surfline, which Long picked up at the lifeguard station where his father worked in San Clemente, California.

　　With three days notice, he would skip school, drive two and a half hours south with his father, and hop a 30-minute boat ride to the islands to see if the swell was arriving as predicted. Often it wasn’t. “We would show up with the expectation that a swell was gonna be hitting, and sure enough it would be 12 hours late and we’d miss it by a day,” said Long, now one of the best big-wave surfers in the world. “It was an early, fun adventure to have that forecast information but still not 100 percent be able to rely on it.”

　　Surfline has since grown into a behemoth. The 100-person company, based in Huntington Beach, California, now comprises a website and mobile app with 5.5 million users who visit an average of 18 times a month to take advantage of its hourly forecasting service and network of more than 950 cameras that live stream waves around the world. (The user and visitation numbers were shared in a May 31, 2023 by then-CEO Kyle Laughlin. The current CEO says they are now inaccurate, but would not offer updated figures.)

　　Thanks to modern technology and 16 full-time forecasters, Surfline’s accuracy at predicting surf conditions has improved significantly since Long’s early trips to Todos. Led by chief forecaster Kevin Wallis, the team now relies on closely held knowledge refined from 38 years of meticulously archived storm-tracking data. Long and Wallis have also developed a close working relationship, consulting frequently on where to chase swells and exactly when to be in the water to meet them at their peak.

　　Long understood that, compared with past storms, the early January swell at Todos Santos that day would be one of the biggest he’d ever witnessed there, the kind that happened once in a decade if you were lucky. “I had probably seen it as big in years past, but that was well before we were physically and mentally prepared, or had the equipment to paddle waves like that,” Long said. “But I always remember seeing it at that size and feeling that, given the right conditions, you could paddle into a wave with a 50-to-60-foot face if you were in the right position. I knew this would be quite possibly the largest I’d ever attempted.”

　　Wallis noticed a critical pattern that helped Long hone in his timing. A day before the session at Todos Santos, offshore buoys to the north spiked pronouncedly as waves filtered past. “Seeing a spike like that on multiple buoys in a row gives you confidence that there should be a peak in the swell at a certain time,” Wallis said. “If I’d seen it on just one buoy, I might not have trusted it.”

　　When the swell passed the final buoy nearest to Todos Santos, Wallis texted Long’s team, which comprised a photographer and two other surfers. “Spike on the Tanner Bank Buoy at 5:40 A.M. That’s 5hrs to Todos so big set around 10:20-10:40.”

　　Long was in the water when the largest set of the day came in, exactly when Wallis predicted. He hadn’t yet caught a wave, and scratched over the first two. He hoped they would groom the choppy surface of the water for the next wave in the set. From his view, the third incoming wave was “an enormous wall of water stretching as far as you could see.” He was in the perfect spot. “I knew right away—that was the biggest wave of my life out there.” He hardly had to paddle to catch it and barely stayed in front of the avalanche of whitewater behind him.

　　As big-wave surfers like Long have learned to ride waves at the upper limit of what the ocean can produce, expert surf forecasters have become essential to moving the sport forward. Long points out that big-wave surfers can now ride massive swells 50 days a year or more, when in the past they’d be lucky to get in a couple such days each season. “Advancements in forecasting are the number one reason that big-wave surfing has progressed so much. There are acute details that only someone like Kevin can read into,” Long said. “Now you can predict almost to the minute when and where it’s gonna be.”