Swell chasing: tracking a wave from the North Pacific to Mavericks

Sofar Ocean

Late April is a relatively uneventful time at Northern California’s Mavericks. The renowned big wave surfing break, which regularly turns out enormous swells during the peak winter months, usually calms in early spring, trading world class waves for less gargantuan sets.

For Grant Washburn, this certainly seemed to be the case on the morning of Friday, April 22, 2022. Washburn, a big wave surfer with decades of experience at Mavericks, was ho-hum on the swells that he was observing from the lineup.

“So this swell came and it was a big swell, but not giant by Mavericks standards.” said Washburn. “Nothing that any of us weren’t used to riding. It was kind of what you’d call ‘average Mavericks,’ which is big waves, but not 50 feet.”

Then, something unusual happened.

“A guy took a small one and I was watching him,” said Washburn. “And right after he fell, I turned around and every single other person was way outside of me bailing their boards as this much bigger wave just ate everyone.”

Seemingly out of nowhere, a large set had sent 15 to 20 surfers into the spin cycle, boards breaking in their midst. Mavericks had thrown a haymaker.

“Even then I was thinking, ‘Yeah, the buoy probably caught this,’” said Washburn.

Months earlier, Washburn and members of the Sofar Ocean team had deployed a Spotter buoy in Half Moon Bay. The device would collect data about Mavericks’ powerful swells, which could then be used to improve the safety measures employed by the local surf scene.

A visualization of the Spotter buoy in Half Moon Bay. The device collects data about Mavericks’ powerful swells. (Spotter not to scale)

Shortly after the wave wiped out the lineup on April 22nd, our team started digging into the Mavericks buoy data — as well as our global forecast data — to see what caused the chaos. Here’s what we found.

Ten days earlier, on April 12, a major storm was heading northeastward through the North Pacific Ocean. Designated Typhoon Malakas, the storm had maximum sustained winds of 109mph on the 12th, but deteriorated three days later.

Though it largely stayed out of the headlines, Malakas did cause a swell to form and propagate across the Pacific. In the video below, watch as the swell caused by Malakas (red storm symbol) moves eastward, causing increases in both significant wave height and peak period as it propagates. The yellow pentagons represent our Spotter buoys and the large white pentagon represents the Spotter buoy in Half Moon Bay, which the swell reached on April 22nd.

After identifying the swell’s origin, we turned our attention to the buoy-level data. If the wave Washburn and his fellow surfers observed was indeed uniquely large, then the Spotter’s historical observations from the morning of April 22nd would make that apparent. First, we plotted the wave heights of all of the waves greater than 5 m recorded by the buoy in the first 18 hours of April 22nd (see Figure 1 below). As expected, the unusual set (represented by the dot within the blue box), which arrived around 11:20am local time, was a clear outlier during the morning surf session.

Figure 1: Each blue dot represents a wave height equal to or greater than 5 m that was recorded by the Spotter buoy at Half Moon Bay during the first 18 hours of April 22nd. The unusually large swell (represented by the dot within the blue box) was a clear outlier during the morning surf session.

An analysis of the buoy’s displacement over time told a similar story. In the video below, watch as the displacement height of the buoy increases then decreases — as each successive wave passes beneath it — with minimal variance during the early morning swell. Then, at 11:22am local time, a pronounced decrease, followed by a pronounced increase in buoy displacement is observed, announcing the arrival of the lineup-clearing swell.

In the aftermath of the wave, Washburn scanned the lineup for injured peers, eventually spotting a dazed surfer in need of help. A man had injured his shoulder and seemed to be concussed, prompting Washburn to initiate a rescue.

“We knew what to do, we did it, there was no panic,” said Washburn. “The guy was back on the beach in a few minutes.”

In the future, Washburn hopes that Spotter buoy data can be used to augment approaches to surf safety at Mavericks and at other breaks around the world. Recently, he presented the data shared in this post with the Big Wave Risk Assessment Group at a summit in Half Moon Bay.

“The crew was very impressed by the depth of data,” said Washburn. “No one has seen a specific wave tied to a buoy report, and the peak waves over 24 hours is also very compelling for safety and rescue, harbor patrol, and, of course, the surfers.”

For more information about the Spotter buoy, check out our Spotter product page. To schedule a demo, please fill out this form.

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