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Surf's up: Calm conditions can last 20 minutes between massive 20-footers

SF Gate logo SF Gate 3 days ago Amy Graff

a group of people swimming in a body of water: Monster swell at big-wave surf spot Mavericks south of Half Moon Bay, Calif., drew hordes of surfers on the morning of Nov. 28, 2018. Liam McNally, the gear editor at the Outbound Collective, was there to catch the action.

Monster swell at big-wave surf spot Mavericks south of Half Moon Bay, Calif., drew hordes of surfers on the morning of Nov. 28, 2018. Liam McNally, the gear editor at the Outbound Collective, was there to catch the action.

© Provided by Hearst Newspapers

A storm system in the northern Pacific is delivering a monster west-northwest swell to Bay Area beaches Wednesday through Friday, and the National Weather Service warns sneaker waves could surprise beach-goers.

"A sneaker wave is when you're standing on the beach and watching the waves and all of a sudden the ocean gets calmer and then suddenly a really large waves comes through," says Matt Mehle, a meteorologist with the NWS's Bay Area office.

Mehle says the surf will be especially big on Thursday and calm conditions could last for 20 minutes between massive 20-foot waves.

The NWS issued a beach hazard statement for Wednesday at noon through Friday at 8 a.m. with the warnings, "Don't be fooled by lulls in between sets" and "Never turn your back to the ocean."

MORE: Mavericks monsters soar to 30 feet before storm, then wave conditions turned 'unsurfable'

The big swell starts Wednesday afternoon when energetic waves known as "forerunners" arrive at beaches. The waves will reach only three to five feet, but Mehle says they have more energy associated with them and can be dangerous.

"It's what's known as an energetic surf zone," he says.

The wave height will increase Thursday with 17 to 20 foot breakers at popular surf spots and especially northwest facing beaches including Ocean Beach, Montara State Beach, Asilomar State Beach and Marina State Beach. The surf could be even higher at big-wave break Mavericks.

See photos above from last week when conditions at Mavericks were ideal for big-wave surfers.

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