Quick Take:

A powerful type of wave referred to as “sneaker waves” are expected to hit the Monterey Bay coastline Thursday. The National Weather Service has issued a high surf advisory through 7 p.m., and the Santa Cruz Harbor will be prepared with rescue boats and staff in case of emergency. The warnings come as a heat wave brings temperatures as high as triple digits to Santa Cruz County.

The National Weather Service has issued a beach hazards statement and a high surf advisory for various regions of the San Francisco Bay Area, including Monterey Bay, as it anticipates “sneaker waves” to hit local coastlines already baking under a heat wave through Thursday evening.

Sneaker waves are very large and often appear unexpectedly following periods of calm waters, hence the term “sneaker.” These kinds of waves typically occur within 10 or 20 minutes of each other and have the potential to sweep swimmers, beachgoers and others out into hazardous waters. According to the National Weather Service, sneaker waves have caused the deaths of more than two dozen people in California and Oregon since 2005.

NWS meteorologist Matt Mehle said that when large swells move into the area and the surf gets very large, meteorologists can tell that sneaker waves may occur by observing “forerunner” waves — smaller waves with a long period of time in between each one, which means each wave has a lot of energy behind it.

“That energy transfers to the beach and then runs up onto the beach,” said Mehle. “So someone might be standing on the beach for 10 to 15 minutes at a dry spot, and all of a sudden, they get a wave that rolls up and knocks them down or sweeps them out to the ocean.”

Credit: Kevin Painchaud / Lookout Santa Cruz

Mehle added that sneaker waves are always occurring, but not all of them make it to the coastline. Most likely, sneaker waves are caused by heavy winds and storms farther out at sea. “Storms create swells, and the swell moves across the ocean, and the leading edge of that swell train is your sneaker wave,” he said.

Mehle said that sneaker waves happen all year long, but winter months usually mean larger storms in the Northern Hemisphere, which can allow for sneaker waves to reach the coastline more often than during other parts of the year.

Santa Cruz Harbormaster Blake Anderson said that while the harbor has advised boaters to closely monitor the water conditions for powerful surges and breaking surf at the harbor’s entrance over the next few days, beachgoers are likely in the most direct danger.

“As a general rule, we tell people to stay off of wet rock, because if the rocks are wet, it’s because a wave reached the area, and it likely will again,” he said, adding that swimmers and surfers can get caught up in large waves as well.

Anderson said that the harbor will not tell people to avoid the water entirely, but as a precaution, the harbor will have staff and rescue boats ready in the channel, making sure boaters preparing to head into the ocean know of the risks.

“It all boils down to your personal experience and how much time you’ve spent in the ocean. If you’re an experienced surfer, and you look at the wave forecast and buoy readings, you can get an idea of what it’s going to be like,” he said. “If you don’t have that experience, you could very well get into trouble.”

The high surf advisory is set to expires Thursday at 7 p.m.

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Max Chun is the general-assignment correspondent at Lookout Santa Cruz. Max’s position has pulled him in many different directions, seeing him cover development, COVID, the opioid crisis, labor, courts...