They are sudden, they are remorseless and they can suck their victims into the sea to an almost certain death. Summoned by wind and tide, these “sneaker waves” hurl themselves far beyond the foam line on the beach then forcefully go in reverse. In the past week alone, they are blamed for the drowning deaths of three people on Bay Area beaches.

Charles Quaid of Richmond was strolling with his wife and dog at North Beach in Point Reyes National Seashore on New Year’s Day when what apparently was a sneaker wave claimed his life. Quaid, 59, was a sailor and familiar with the ocean but still disappeared into a churning sea. Quaid’s dog emerged from the water unharmed.

A similar tragedy occurred Dec. 28, when 37-year-old Juan Escamillo-Rojas of San Francisco died trying to save his 9-year-old son Juan Carlos Escamillo-Monroy, after a wave swept the boy into San Francisco Bay as they fished off the Marin Headlands. The boy also died.

In the aftermath of those tragedies, Bay Area families that once frolicked in the foam at places like Monastery Beach near Carmel and Pleasure Point in Santa Cruz, retreated from the threat of killer waves with the malevolent recoil of a bullwhip. Yet as unusual as the deaths were, sneaker waves are not uncommon at this time of year. “Everyone is talking about these waves that run up on the beach and snatch dogs and families and drowns everyone,” said Mark Massara, who has surfed Northern California waters for more than 40 years. “And the dog always survives.”

Pattern waves

Massara, who is general counsel for the wetsuit manufacturer O’Neill, thinks the term “sneaker waves” was concocted to make people feel better about their own ill-advised daring. “If it helps the public be more sensitive to the inherent dangers of the ocean in Northern California in the winter, I suppose it’s OK,” he said. “But if you’re trying to describe what goes on in the ocean, it’s entirely misleading. There aren’t sneaker waves. There’s regular, routine, predictable giant surf in January in Northern California.”

The cold-weather phenomenon claimed most of a family in November. They were playing fetch with their dog on Big Lagoon Beach in Humboldt County, when they were swept into the ocean by a sneaker wave while their teen daughter helplessly watched from the shore. Howard Kuljian ran into the churning surf to save the family dog, Fran, and he was followed by his wife and their son, Gregory. All three drowned; the dog survived.

Despite popular mythology that has sprung up about the predictability of waves — it’s not true that every seventh wave will be a big one — they do often arrive in sets that follow a pattern. Generally, sneaker waves occur when two large peaks converge and suddenly create a monster, such as the one that swept ashore during the Mavericks surf competition three years ago, injuring 16 spectators.

“On a steep beach, that wave will run up and rush back pretty quickly,” said Gary Griggs, director at UC Santa Cruz’s Institute of Marine Sciences. “If the tide’s coming in, that’s going to act in concert with those converging waves.”

Sneaker waves sometimes claim victims standing in relatively calm water, which is what happened to environmental activist Rebecca Tarbotton, 39, of Oakland. She died Dec. 26 after being tossed around by a big wave not far from a beach north of Puerto Vallarta, Mexico. And as Tarbotton’s death demonstrated, knowing the tremendous power that nature can release in an instant offers little protection. One of Northern California’s most popular diving spots is Monastery Beach near Carmel, which the expert divers who flock there refer to as Mortuary Beach because it has taken so many lives.

Surprising ocean

While oceanographers tend to dispute the notion that killer waves are consistently rising out of the sea and dragging innocent strollers to a watery grave, even they are sometimes caught off guard by the unanticipated arrival of an extremely large wave. “I think it’s a pretty good description,” said Oregon State University oceanographer Robert Holman, referring to the phenomenon’s unusual name. “They lie well out of the statistical expectation of what the next wave should be.”

He ought to know. A few years ago, Holman and his wife were standing on a rocky point by the sea in Italy when they were suddenly consumed by a wall of water that he never saw coming. “I got totally drenched,” he recalled. “That was a surprising moment.”

It can happen to anybody.

“In general, some people are not very good observers,” Griggs said, “or they’re not really thinking carefully about what they’re being exposed to. If you’re walking on the wet sand, you’re probably walking where the water has been a few minutes before. If the sand is dry, it’s unlikely you’re going to be swept out to sea. But we’ve all seen people who put their towels down on the beach, and as the tide comes in, all of a sudden their towel is underwater.”

Griggs once went to the home of an elderly woman in Santa Cruz, hoping to reassure her that the waves pounding just off her rear deck wouldn’t wash her home away. “Just as I turned around, this wave came up and just covered me,” he said. “As I walked into her house, soaking wet, she said, ‘Never turn your back on the ocean.”’

Contact Bruce Newman at 408-920-5004; follow him at Twitter.com/BruceNewmanTwit.

beach safety rules

• Never turn your back on the water.

• Be mindful of upcoming weather conditions.

• Be aware of potentially dangerous waves in areas of strong currents that are near shore or shallow banks.

• Remember that sneaker waves are hard to predict.

• Remain aware of your surroundings.

• Do not play on the rocks.

• Do not overestimate your swimming abilities.

• Do not underestimate the power of the sea.