Mavericks breaks on a reef about half a mile off Pillar Point Harbor in Half Moon Bay, roughly 25 miles south of San Francisco. It produces some of the largest rideable waves in the world, with faces often reaching 40 to 60 feet during big swells and sometimes topping 80 feet. The wave is seasonal, because it needs a particular kind of swell that only North Pacific winter storms send from the right direction. The shape of the seafloor then focuses and amplifies that energy at the reef. As a result, the wave barely exists in summer but becomes one of the most powerful on the planet from November through March. When it peaks and what makes the biggest days comes down to how Pacific storms meet California's coastline.
Mavericks swell forecast
Loading the NOAA swell forecast for Pillar Point…
Source: National Weather Service marine forecast and NOAA buoy 46012.
Why Are the Waves at Mavericks So Big and Dangerous?
The Mavericks reef is an underwater rock shelf that rises steeply from about 50 feet deep to about 20 feet over a short distance. When a large swell hits this shelf, its energy is squeezed and forced upward into a steep, fast, heavy wave with a distinctive bowl shape. The reef faces northwest, the direction North Pacific winter swells come from after traveling thousands of miles from storms near Alaska, the Aleutian Islands and the central Pacific. The reef's angle, the deep water around it and a gap in the coastal shelf that lets swell reach it at full strength all have to line up. Few places on Earth have that combination.
The wave is also notoriously dangerous. The cold winter water, in the low to mid 50s, the shallow reef, strong currents and heavy sets that can trap surfers inside all add to the risk. Wipeouts at Mavericks are severe, and being held underwater in heavy surf can be fatal, as it has been for experienced surfers. Mavericks is not a spot for recreational surfers, and on big days the lineup is a small group of specialized big-wave athletes.
Peak Season: November to March
The Mavericks season runs from about November through March, matching the North Pacific storm season. October sometimes brings early swells and April can bring late ones, but most big Mavericks days fall in the core winter months. December and January are usually the most productive, with February close behind. That is when the North Pacific storm track is most active and storms are often big and organized enough to send the long-period swell Mavericks needs.
In a typical December, the biggest reading at the NOAA buoy off Half Moon Bay reaches about 20 feet, roughly twice the biggest reading in a typical August. Swell big enough for Mavericks, about 12 feet or more at 15 seconds or longer, arrives on about five days a month in December and January. From May through September it almost never shows up.
The swell direction that makes Mavericks work is northwest, roughly 300 to 315 degrees. West swells produce rideable but less powerful waves, while northwest swells hit the reef at the angle that creates its bowl shape and biggest faces. Swell period matters too, meaning the time between waves. Swells of 18 to 20 seconds or longer carry more energy from deep water and build larger faces at the reef. The best days combine a solid northwest swell, a long period and a light offshore wind in the morning. The same long-period swells drive sneaker waves on nearby beaches, so spectators should stay well back from the water.
Deep Dive: How Does the Reef Build a Giant Wave?
Mavericks turns ordinary winter swell into giant surf by changing the depth of the water under it very quickly. Waves slow down as the water gets shallower. That slowing bends the swell toward the reef and squeezes its energy into a shorter, taller wave. When the wave grows too tall for the water beneath it, it breaks.
Why Do Waves Slow Down and Bend Over the Reef?
An ocean wave moves water in circles that reach down about half a wavelength. By our calculation, an 18-second winter swell has a wavelength of about 1,650 feet in deep water. It starts to feel the seafloor once the water is shallower than about 800 feet, well before it reaches the reef.
From then on, the wave's speed depends on the depth. By our calculation, it moves at about 27 mph over 50 feet of water but only about 17 mph over 20 feet. The part of the wave over the shallow reef slows first, while the parts on either side, over deeper water, keep moving faster. The crest swings around toward the shallow rock, much as light bends through a lens. Scientists call this refraction.
Detailed maps help explain why the effect is so strong here. The Monterey Bay National Marine Sanctuary described new high-resolution seafloor images of Mavericks in 2007, from a statewide project mapping California's coastal waters. The sanctuary noted that the bedrock reef's abrupt shape concentrates wave energy, so the wave slows, shortens and grows taller.
When Does a Wave Get Too Big for the Water?
As a wave slows, its energy has nowhere to go but up. The wave shortens and steepens, a process called shoaling. At some point the water beneath it can no longer support the crest, and the top pitches forward.
A classic rule of thumb, worked out by the mathematician John McCowan in 1894, says a wave breaks when its height reaches about 0.78 times the water depth. By our calculation, a 40-foot wave would start to break over about 50 feet of water. That is right where the Mavericks reef begins its climb toward 20 feet.
The steepness of that climb is what makes the wave so heavy. On a gently sloping beach, a wave loses energy gradually as it breaks over a long distance. At Mavericks, the depth changes so fast that the wave has almost no time to adjust. It jacks up and throws its lip forward all at once, which produces the thick, hollow walls the reef is known for.
Is the Mavericks Contest Still Held?
The Mavericks big-wave contest has not been held since February 2016, when Nic Lamb won the last event. The World Surf League took over the contest after that season and cancelled it indefinitely in 2019, citing logistical problems. When the contest did run, organizers waited through the winter for a big enough swell and then called the event with only 24 to 48 hours of notice. Big swells still reach the reef every winter. To see Mavericks at its best, watch the swell forecast and go on a morning with a large northwest swell.
You can watch from shore at Pillar Point, where the bluff and rocky shoreline look out toward the break. Because the break is half a mile offshore, binoculars help for watching surfers in the lineup. Stay on the bluff and well back from the water, because the long-period swells that build Mavericks also send sneaker waves far up the beach.
The surrounding area of Half Moon Bay in winter is itself interesting for weather observation. The coast at this location is fully exposed to the Pacific, and winter swell days bring significant wave energy to the surrounding beaches as well. The dramatic combination of large surf, gray winter sky, and cold clear air that characterizes a Mavericks day is also a compelling coastal experience even for non-surf observers.
Summer at Mavericks
In summer, the water over the Mavericks reef is usually flat. The North Pacific High dominates the weather and storms track far to the north. Summer swells come from the Southern Hemisphere at angles that do not light up the reef. The harbor at Pillar Point is calm and busy with fishing boats, and fog covers the coast much of the time. Looking at the flat water in July, you would never guess how powerful the same spot becomes a few months later.
