What Is a Sneaker Wave? How to Avoid Bay Area Beaches’ Hidden, Deadly Hazards

And while “the worst of it looks like it’s behind us,” Flynn said he “wouldn’t be surprised at all if we end up extending this at least to the end of this week.”

“Typically, a beach hazard statement goes out for like two, three days,” he said. “So this is out of the ordinary.”

Flynn said sneaker waves are especially common at Bay Area beaches, so read on for his top tips on staying safe by the water this week and through the summer.

Or jump straight to:

• Beaches in the Bay Area with sneaker wave risks
• How to stay safe from sneaker waves
• What to do if you or someone you see gets swept out

What causes sneaker waves, and how can they be predicted?

Flynn explained that sneaker waves come from ocean swells that are spaced far apart from one another, called “long period swells.” Over time and distance as they head from the middle of the ocean toward a beach, these swells build up speed and power, which creates bigger waves and stronger currents, and increases the risk of sneaker waves.

In this case, the long-period swells are being caused by strong trade winds in the tropics, near the equator, Flynn said. “So these waves were generated days ago, and it’s just been really persistent,” he said.

The National Weather Service monitors these conditions with buoys in the ocean and satellites that measure wind speed and wave height. They also look at weather models to predict average wave heights.

But despite this technology, individual sneaker waves can’t be forecasted and might “look like every other wave” to someone on the beach, Flynn explained. So their power and distance — sometimes traveling twice as far upshore as the rest of the waves — often take people by surprise.

“If you’re in a boat, you might not even notice them, but when they hit the beach, they have a long time to build up and then they take a long time to go back out,” he said — “and that can create hazardous conditions on the beach.”

Eventually, Flynn said, the winds should stop or change direction, but the risk of sneaker waves won’t immediately be reduced because of the delay in the time between when the waves are generated and when they hit the coast.

“We just have to wait for the ones that are still out there in the ocean to hit the coast, and we’ll go back to normal conditions,” he said.

What types of beaches have sneaker waves?

This depends on the direction the swell is coming from, Flynn said. Right now, as is common during the summer months, the swell is coming from the south and southwest from strong trade winds in the tropics, so it’s likely to affect south- or southwest-facing beaches the most. Around the Bay Area, that would include beaches like:

• Limantour Beach in Point Reyes
• Surfers Beach in Half Moon Bay
• Several beaches in the Santa Cruz area.

Conversely, in winter, north-facing beaches are a bigger risk, Flynn said. But this can change, and the unpredictability of these waves means that they “can come from any direction — and then that would change where the highest threat level is,” he said.

The slope of the beach itself matters, too, Flynn said: A flatter beach gives the swell a runway to travel extra high up the beach, but may be less of a risk of dangerous breaking waves. A steeper beach, on the other hand, can cause breaking waves to build higher and higher — “so the hazards shift,” he said.

What should you do to avoid sneaker waves?

First, don’t ever turn your back to the ocean, Flynn said.

“If you’re going to be close to the water line, make sure you at least have one eye on the water to see if one of these things is coming,” he said.

You can also be prepared by keeping an eye on the tide tables, he recommended — and know that low tide is more dangerous than high tide because it catches people off guard.

“High tide is more hazardous in terms of total water; the water will push further up, but it’s usually not as much of a surprise at high tide as it is at low tide,” he said.

So, at low tide, “be extra cautious if you’re going to set up your blanket or your chairs,” he said. “Even if you seem well set back currently, the tide could rise six or seven feet over a couple of hours.”

When you first get to the beach, Flynn advises standing and watching the water for around five minutes before picking a spot to post up. But remember: “Even if you do that, just know you can always get a sneaker wave that goes twice as high up the beach as everything else was,” he said. “So always keep that threat in mind.”

What happens if you get caught in a sneaker wave or if someone near you does?

Most of the time, Flynn said, a sneaker wave will wash ashore higher than expected, flow up and over your knees and soak your things — maybe even knocking you over.

But there is the occasional wave that will pull people fully into the water.

It’s easier said than done, Flynn said, but the most important thing to do if this happens is to “remain calm.”

That’s because the real danger lies in the rip current that keeps people out in the water and away from shore, “that drags you deeper and deeper, and that rip current is stronger than you can swim,” he said.

“The only way to safely navigate it is not to fight it,” he said.

So here’s what you should do if a sneaker wave pulls you into the ocean:

1. Relax your body
2. Just try to float
3. When you’re calm, try swimming perpendicular (not parallel) to the shore to get out of the current
4. Once you stop feeling the pull of the water, make your way back to a beach

If you are on the shore and see someone else get pulled out into the water, “stay on the shore,” Flynn said. Too often, people will try to swim out to save a dog or person and get caught in the current, too, creating an even more risky situation.

What you can do to help is shout out to the person the instructions above, get the help of a lifeguard or call 911.