Why so many people are getting swept to sea along California's coast

A magazine editor visiting from Salt Lake City was walking along a Humboldt Bay jetty with her son.

A school principal was on vacation, taking family photos by the sea in Mendocino Big River Headlands State Park.

A father and his two young children were spending a Sunday at Blind Beach in Sonoma Coast State Park.

A man in his 30s was hiking with friends along the coast in the Marin Headlands.

A man and woman were searching for mussels on the rocks at Pescadero State Park.

Then came the waves.

Each of these people was swept from dry ground into the frigid, turbulent sea. Each faced the shock of the cold, the pounding of incoming, indifferent waves.

Three were pulled from the sea during difficult rescue attempts and pronounced dead shortly thereafter. Four are still missing and presumed dead. One — the still unnamed man who was searching for mussels — is in the hospital.

All of these incidents occurred along California's coastline over the last five weeks. Three took place over the weekend. It feels like the right time to ask: Is this normal?

Yes and no.

"The way this winter season is going, there has been a lot of strong storm activity across the North Pacific that's responsible for these wave trains coming in," said Rick Canepa, a meteorologist with the National Weather Service. "There's nothing unusual about the timing."

The surf off Northern California tends to become more dangerous starting in November and lasting through February and sometimes into March, Canepa says. (And that's on top of the day-to-day dangers of the sea, which are ever-present, he adds.)

But then Canepa brings up a recent storm that was unusual: a bomb cyclone that slammed Alaska's Aleutian Islands over New Years with waves over 50 feet high and winds up to 109 mph. It was one of the strongest storms to ever impact North Pacific, according to the NWS Ocean Prediction Center, and its "rip-roaring" jet stream is likely to have delivered weather disturbances to the Pacific Northwest and California over the following week.

It's difficult for meteorologists to say whether the waves that claimed lives along the California coast in early January were a direct result of the storm. But generally, it takes waves around three days to travel from the Gulf of Alaska to California, says NWS meteorologist Duane Dykema. The incidents at Mendocino Big River Headlands State Park and Sonoma Coast State Park took place on Jan. 2 and Jan. 3, respectively.

In all of the incidents, larger than usual surf had been generated by a storm somewhere in the ocean, and waves were larger than a normal day at the beach. Multiple storms may have combined swells to create larger waves known as set and sneaker waves. Set waves are larger and more powerful than the waves in between, and can be timed (and often are by surfers) because they are somewhat predictable.

Sneaker waves are less predictable and larger than the set waves. They can catch people off guard in areas they perceive to be safe, knocking even the most experienced ocean swimmers off their feet and into the water. They can surge more than 150 feet up the beach. They can lift logs out of the sand.

In an emailed response to an SFGATE inquiry about the recent incidents, a California State Parks official stated that while the coast of Northern California is "notorious" for having large swells during the wintertime, the number of fatalities varies from year to year.

Variables can include weather, swell size, time of year, beach dynamics and size of tides, the email stated, and on average the agency sees about four to six deaths on the ocean along Northern California per year. If you count the people still missing, the California coast has seen more than the average number of yearly deaths over the past five weeks.

"Our hearts go out to the family of the victims of the recent incidents," the agency's email stated. "State Parks lifeguards continue to make heroic rescues in huge surf and educate our visitors to keep them safe, preventing potential emergencies."

A High Surf Advisory is in effect from 10 a.m. Tuesday through 3 p.m. Wednesday for the coast from Sonoma County south to Monterey County. King tides will continue through midday Tuesday, resulting in minor coastal flooding. Dangerously large waves of up to 30 feet are likely to been seen at favored breakpoints, and there's a high risk of strong rip currents and sneaker waves.

"Beachgoers, surfers, and mariners should be prepared for dangerous waves in the surf zone and increased rip current activity," the NWS stated in a press release. "Stay off rocks and coastal jetties and keep children close and pets on leashes."