Monstrous 20- to 25-foot waves are forecast to wallop the Pacific coastlines in Northern Oregon and Southern Washington Friday afternoon.

Portland’s National Weather Service office warns that high seas and strong maritime winds will make for hazardous boating conditions between Thursday night and Friday. Breakers will reach 8 to 13 feet starting Thursday night. Swells will continue to build into Friday when 15- to 25-foot waves will be possible. Waves in this range will continue to hammer the coast throughout the weekend.

“It’s a good time to stay on land,” the NWS said.

Strong maritime winds will also be possible between Thursday night and Friday, with 25 to 35 knots gusts. The NWS has issued a gale warning for coastal waters from 2 p.m. Thursday to Saturday morning.

“Saturday night and Sunday, winds gusting 25 to 30 knots will persist,” the NWS predicts. “This will send another swell surge, which appears will be strong enough to build combined seas back to or above 20 feet on Sunday.”