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California's coast is bracing for the biggest surf in years. Forecasters expect breaking waves of 30 to 40 feet along exposed Northern California beaches from late Friday, November 13, through Saturday — with individual offshore waves that could top 50 feet, and waves at the famed Mavericks surf spot south of San Francisco expected to reach 60 feet or higher. The National Weather Service has issued high-surf warnings up and down the coast and put it bluntly: the risk of drowning is very high this weekend. The waves are not a freak event. They are the product of three forces arriving at once — a strengthening El Niño, a parade of Pacific storms, and an atmospheric river — and understanding how they combine explains why this weekend is different from an ordinary big-swell day.
The numbers: what is actually forecast
First, a necessary distinction, because wave numbers are easy to misread. When forecasters talk about "significant wave height" — the average of the highest third of waves — the numbers for Saturday morning are 20 to 30 feet from San Francisco to Crescent City. But the actual highest waves can be roughly twice the significant height, which is how individual offshore waves could exceed 50 feet. The National Weather Service's high-surf warnings are more specific by place: 25-to-35-foot breaking waves for parts of Humboldt and Mendocino counties Friday into Saturday, 25-to-30-foot surf possible around San Francisco, and 8-to-12-foot waves as far south as Los Angeles and San Diego. At Ocean Beach in San Francisco, waves could reach more than 40 feet; at Mavericks, 60 feet or higher.
The rain that comes with the swell is real but modest by comparison. The first storm brings rain up and down the state on Friday, arriving in the North Bay as early as late Thursday night, with between half an inch and 1.25 inches expected there. The heaviest rain is likely in the North Coast region, where up to six inches could fall over the next week, while the San Francisco Bay Area could record up to two inches and Los Angeles less than an inch. In the Sierra Nevada, a winter storm warning calls for up to 20 inches of heavy, wet snow along the crest west of Lake Tahoe, with ridge gusts of 70 to 90 mph. The flooding risk from rain is predicted to be low — the danger this weekend is the ocean, not the rivers.
Three ingredients: El Niño, a parade of storms, and an atmospheric river
The first ingredient is the one this blog has already been tracking: El Niño is strengthening, and the waters off California are unusually warm. Warm water does two things. It feeds storms, giving them more energy, and it raises sea level — El Niño-warmed seas are pushing tides more than a foot higher than in a typical year, so the same waves reach further up the beach than they otherwise would. The storms now arriving are the first prolonged stretch of widespread stormy weather of the season, and forecasters expect them to be followed by more: seven or eight pulses of energy are possible through the week of Thanksgiving, keeping the ocean unsettled for weeks.
The second ingredient is the "parade of storms" itself — a succession of powerful lows churning the Gulf of Alaska and the North Pacific, each one throwing long-period northwest swell toward the California coast. Long-period swell is the key detail: waves that have travelled thousands of miles arrive in organised, powerful sets, and they break harder and further up the beach than short, choppy local wind waves. The latest storms are expected to rapidly intensify about 1,200 miles off the coast, and modelled seas within that distance of San Francisco Bay could reach 45 to 50 feet.
The third ingredient is the atmospheric river — a narrow ribbon of concentrated moisture in the atmosphere, sometimes called a river in the sky — that is funnelling rain toward the West Coast as the moisture stream shifts south. It is the atmospheric river that turns a big-swell event into a full storm system: soaking rain, howling wind, and the enormous surf arriving together, rather than one at a time.
Why the danger is not the size alone
Fifty feet is a striking number, but the National Weather Service's warning is not really about the number. It is about what big surf does to people who are not in the water. The agency cautions that waves can sweep across the shoreline without warning, dragging people off beaches, rocks and jetties — the so-called sneaker waves that arrive between ordinary sets and catch onlookers by surprise. Add rip currents, which pull even strong swimmers away from shore, and the risk extends to anyone standing at the water's edge to watch.
That is why the advice is so simple and so absolute: never turn your back on the ocean. Stay off rocks and jetties, keep well back from the waterline, and do not go in to watch the surf up close. The biggest waves in years are also a reminder of the season now opening: with El Niño strengthening and a parade of storms lined up through Thanksgiving, this weekend is likely the first of several, not a one-off. The storms will replenish reservoirs and soak the landscape enough to reduce the wildfire threat — but for anyone heading to the coast, the message is to admire the ocean from a safe distance, and to remember that the wave you do not see coming is the one that matters.