LOS ANGELES (AP) — Powerful surf rolled onto beaches on the West Coast and Hawaii on Thursday as a big swell generated by the stormy Pacific Ocean pushed toward shorelines, causing localized flooding.

Forecasters urged people to stay off rocks and jetties, and to not turn their backs to the ocean because of the danger of “sneaker waves” — occasional much bigger waves that can run far up the sand and wash someone off a beach.

A high surf warning for parts of Northern California said waves would range from 28 to 33 feet (8.5 to 10 meters) and up to 40 feet (12 meters) at some locations, the National Weather Service said, adding that there were reports of flooding in low-lying coastal areas.

In Aptos on the north end of Monterey Bay, surf overran the beach and swept into a parking lot, leaving the area strewn with debris. Santa Cruz County issued warnings for people in several coastal areas to be ready to evacuate.

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“Mother Nature’s angry,” said Eve Krammer, an Aptos resident for several years. “I mean these waves are gnarly. They’re huge.”

The same area was battered by the ocean last January as the West Coast was slammed by numerous atmospheric rivers.

“I feel for the people that are down low here,” said Jeff Howard, also an Aptos resident.

While not quite as huge, the waves along Southern California were also described as hazardous, with life-threatening rip currents. Nonetheless, surfers couldn’t resist.

Patience was key, according to Alex Buford, 27, who was catching waves just north of Manhattan Beach on the Los Angeles County coast.

“I was waiting for awhile because the waves were really sick, and they’re kinda hard to get into even though I have a really big board,” he said. “Just waited for a good one and I got it and it was a long one. Pretty big. It was sick.”

In Hawaii, the weather service forecast surf rising to 30 to 40 feet (9 to 12 meters) along north-facing shores and 18 to 22 feet (5.5 to 6.7 meters) along west-facing shores of five islands.

Professional Hawaii surfer Sheldon Paishon was getting ready to surf Thursday morning at Makaha, a world-famous surfing beach on Oahu’s west side.

Paishon, 30, has been surfing at various spots around Oahu this week, taking advantage of waves during this week’s high surf warning in effect till Friday morning.

“It’s always big waves in the winter time in Hawaii,” he said.

He warned that novice surfers should check with lifeguards before heading into the water and “make sure you got some people around you and stay safe.”

Honolulu Ocean Safety lifeguards, posted at beaches across Oahu, rescued 20 people along the island’s famed North Shore on Wednesday, said spokesperson Shayne Enright. They were also busy with thousands of “preventative actions,” she said.

“This time of year produces incredible surf but it can also be very dangerous,” she said.

The dangerous surf could also cause surges that could hit coastal properties and roadways, the weather service warned.

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Jennifer Sinco Kelleher reported from Honolulu.