HALF MOON BAY (CBS SF) — A storm front moved toward the San Francisco Bay Area Wednesday morning, kicking up a large northwest swell that could trigger 20-25 foot waves at the legendary Mavericks surf break off the San Mateo County coast.

The National Weather Service has issued a high surf advisory until mid-afternoon for coastal beaches.

READ MORE: Peloton Tread+ Owners Told to Stop Using Treadmill in 'Urgent Warning' From Gov't Agency

“This swell will quickly build today generating large breaking waves of 15 to 20 feet, locally up to 25 feet at favored breakpoints,” weather service forecasters said.

Webcams at Mavericks were already capturing the evolving swell and more than a dozen big wave surfers in the water and catching waves.

Waves were forecasted to grow mid-morning and be at their highest all afternoon long.

For beachgoers, forecasters warned of the dangers presented by sneaker waves and strong rip tides.

“Sneaker waves and large breaking waves can sweep people off jetties and docks, and into dangerous seas,” Forecasters said. “Cold water rescues or drownings are more likely with these waves and stronger rip currents.”

Last week, similar big wave conditions swept two people off beaches in Pacifica. A woman pulled from the waters by a pair of Good Samaritans. Meanwhile, a man was presumed dead after he was was swept away off the rocks near Beach Boulevard and Paloma Ave.

Among the areas most exposed to the northwest swells are San Francisco’s Ocean Beach; San Mateo County’s Montara State Beach; Monterey County’s Marina State Beach and Monastery Beach in Carmel.

“These large waves can be erratic and unpredictable and may injure or knock beachgoers into the cold, turbulent ocean,” forecasters warned.

READ MORE: Father, Child Die In Early Morning Oakland Fire; Deaths Being Investigated As Homicides

Meanwhile at Mavericks last week, the high surf conditions drew some of the world’s most talented surfers as 30–to-40 foot waves were breaking just off Pillar Point.

“It was good out there,” said surfer Chase LaRue. “There are some bombing sets. There are some living legends out there, just catching basically anything that’s coming through.”

It was a picture perfect day for world class surfing and the talented big wave surfers put on a spectacular show. Like every Mavericks, watching was both exhilarating and horrifying. Those coming off the water found themselves comparing the day to epic years past.

“Once, I think it was like 2016, it was like this, just out of control, huge, scary,” laughed Connor Beatty. “I was doing the same thing, sitting at the channel, watching.”

“I was hoping that I could get one wave for my country,” said Hide Minami of Japan. “I got the one wave, inside, small one. Outside, big ones? Untouchable for me.”

“I didn’t break my board,” Beatty laughed. “So I’m stoked.”

Also stoked were the spectators who found themselves watching the sudden revival of this famed event.

“It’s a big crowd,” said Richard Patterson. “Once the word gets out. It’s getting more and more popular.”

Those crowds can also still eat outside in San Mateo County.

MORE NEWS: Woman Dies in Saturday-Morning Rollover Crash on I-580 in Oakland

“Oh yeah, and that’s a big thing,” said Scott Sutton. “That place we were just at across the street, they were serving a lot of people. It was huge.”