A persistent ocean swell is creating dangerous conditions along the coast from Sonoma County to Big Sur, according to the National Weather Service.
From 10 a.m. Wednesday through 4 p.m. Thursday, the entire coast in that area will be impacted by a west-northwest swell that has the potential to bring with it dangerous sneaker waves, stronger rip currents and moderate to large breaking waves.
"Sneaker waves occur when long-period swells arrive in sets at the beaches. This means there may be lulls up to 30 minutes between the larger sets that run much farther up the beach and can catch people off guard," according to the weather service.
Some of the beaches that are expected to experience such conditions are Ocean Beach, Montara State Beach, Half Moon Bay State Beach, Manresa State Beach and Marina State Beach.
"Steep beaches will have a higher risk of sneaker wave activity with greater wave run-up onto beaches. Occasionally larger waves will also wash over jetties and rock outcroppings that normally stay dry," according to the weather service alert.
A similar alert is in effect for southern Humboldt County and all of Mendocino County.