A high surf warning remained in effect until Sunday morning for what the National Weather Service called “life-threatening” waves of 25 to 35 feet, with the potential for 50 to 60 feet at steep shorelines such as Mavericks in Half Moon Bay. As of 9 a.m. Saturday, significant wave heights—the average of the highest third of waves—reached 31 feet at a buoy offshore Point Reyes, the second-largest reading in three decades of records. Only December 2015 saw bigger waves, by less than a foot.

In Pacifica, large waves crashed over the seawall throughout the day, but every 20 to 30 minutes a wave that appeared to be double the size pushed water hundreds of feet inland, flooding city streets. Onlookers were soaked by towering water, and some were knocked off their feet and sent scrambling. Near the Pacifica Pier, a constant stream of spectators flocked to the waterfront on foot despite closures on adjacent streets. Several people, including a mother carrying a toddler, were caught in a sneaker wave and knocked down in the parking lot in front of the Pacifica City Council Chambers. The mother and toddler were able to get up with help from bystanders who immediately rushed to assist.

Rocks, kelp, and other debris surrounded the Taco Bell Cantina, and nearly a foot of floodwater along Highway 1 prevented cars from entering the parking lot. Erin Shea, a renter at the end of Elder Lane, said floodwater damaged personal belongings in her garage. Adam Drake, a beachfront homeowner farther up Elder Lane, described the scene as “unprecedented,” with only 2023 bringing more furious flooding. Recently installed pumps were not working to drain floodwater at the end of the road, he said.

Marc Ramos, who surfs at Rockaway Beach at least twice a week, said Saturday’s rip currents made surfing impossible. “This is just the beginning of the surf season,” Ramos said. “I’ve seen it like this, but in mid-January. This is kind of odd. We haven’t even hit Thanksgiving yet.” He warned that anyone getting too close to the waves could be swept out to sea quickly. “Don’t go out,” he said. “Definitely don’t go out.”

In San Francisco, about 50 people stood along Ocean Beach near Sunset Dunes park watching the waves late Saturday morning as the tide reached the dune in front of the parking lot. Emir Molina, who has fished at Ocean Beach since moving to the city 26 years ago, said the waves were the biggest he had seen in all those years and were far too large to fish. “I have a ton of respect for the ocean,” he said. “A ton of respect.”

In Marin County, Richard Delameter came to Point Reyes Beach from Novato to watch the spectacle. “Why am I here? Because nature, when she is furious, is completely dramatic. I like the drama of watching the earth when she’s angry,” he said. Delameter, who has visited Point Reyes since 1967, said a ranger had told him to move to higher ground earlier in the day.

U.S. Park Service volunteer Susan Aaron said the sunshine and relatively light breeze were moderating the effects. “If the wind was blowing another 20 miles per hour, the waves would be right up to the base of the dunes,” she said. Aaron said she expects this winter to bring extensive damage to the California coast. “The coastal communities are in real trouble. People are unaware of the power of nature.”

The Santa Cruz County Sheriff’s Office issued a weekend evacuation warning for low-lying coastal areas due to significant wave activity and hazardous surf conditions. “Large waves have the potential to reach coastal homes and properties, causing dangerous flooding and making access to affected areas difficult or unsafe,” the sheriff’s office said.

The National Weather Service warned spectators to keep a safe distance from the waves all along the coast. “Dangerously large breaking waves can overpower swimmers, pulling people into the sea from beaches, jetties, and rocks resulting in significant physical injury and increasing the risk of drowning,” the agency said. “Waves can sweep across the shoreline without warning.”

Huge waves are a hallmark of El Niño, and experts say repeated rounds of waves this winter could cause billions of dollars in damage along the California coast, especially if they hit during high tides. “El Niño-driven changes in tropical weather patterns are shifting storm paths across the North Pacific, bringing stronger storms and bigger waves to the California coast,” the Scripps Institution of Oceanography said in a social media post. “During El Niño, storms also tend to track farther south, forming closer to California and increasing wave activity along the coast.”

Scripps noted that typically the largest waves arrive in December and January, and only once in the 27-year record of the Point Reyes buoy have forecast wave heights been this large in November. The relationship between wave heights and energy is squared, meaning a 40-foot wave slams the coast with four times as much energy as a 20-foot wave. Along the California coast, wave power is 32% stronger during strong El Niños than in a typical year. Wave-producing storms are becoming larger with climate change, and rising sea levels are contributing to more coastal damage, previous research has found.

Another large swell was expected late Sunday into Monday, with rough seas continuing through the week as more storms spin off the California coast. Forecasters and local officials urged residents and visitors to stay away from the water and heed evacuation warnings.