You may not have heard of them before, but sneaker waves are one of the most dangerous weather-related hazards on beaches, And along much of the West Coast, they are one of the most deadly by far.

Sneaker waves may not be talked about as much as rip currents, but they are a threat that warrants your attention if you’re going to the beach.

What is a sneaker wave?

A “sneaker wave” is a wave that literally sneaks up on you.

They arrive seemingly without warning, and they can surge farther up the beach than any other waves before or after, some reaching over 150 feet onto the dry beach.

A sneaker wave can strike after 10 to 20 minutes of smaller waves, so it’s not surprising if you feel safe and unconcerned.

(MORE: Rip currents explained: how they form, how to spot them and how to escape)

Because these waves come so suddenly, they can be potentially fatal. Sneaker waves kill more people along the West Coast than all other weather hazards combined, according to the National Weather Service (NWS).

Troy Nicolini, the meteorologist-in-charge for the Eureka NWS office in California, told Bay Nature that an estimated five people each year die from sneaker waves from Central California through Oregon.

Not only can these waves sweep people out to sea, but they can also lift logs and debris on the beach weighing hundreds of pounds, rolling them up and then back down the beach, potentially pinning beachgoers under their weight.

In the Northwest, the waters offshore are often extremely cold. Anyone getting swept away by a sneaker wave could experience cold water paralysis and hypothermia from the sudden exposure. Cold water paralysis can set in and affect your limbs within minutes, making it harder to swim to safety or tread water.

Sneaker waves also carry large amounts of sand, water and gravel that can be deposited in beachgoers’ clothes, which can weigh them down and make it easier to be swept out to sea.

How to stay safe

Sneaker waves can happen anywhere, but they are especially concerning and prevalent along the West Coast due to the cold waters and rugged coastline.

Before you go to the beach, check local forecasts for any mention of increased sneaker wave threat, like the forecast discussion from the San Francisco NWS office below.

The NWS also warns to stay off of jetties, rocks and outcroppings and avoid steep beaches.

Never let your guard down, and never turn your back on the ocean. This is especially true if sneaker waves are a threat for your area. Listen carefully to the water, and study its wave patterns before you even think about getting comfortable.

Remember that no place on the beach is too far from the water’s edge for a wave to reach, and they can move with surprising speed.

When you do settle in, do so away from any fallen logs or debris fields on the beach near the surfline or below the high water marks.

Sara Tonks is a content meteorologist with weather.com and has a bachelor’s and a master’s degree from Georgia Tech in Earth and Atmospheric Sciences along with a master’s degree from Unity Environmental University in Marine Science.