SAN FRANCISCO—According to the National Weather Service, Bay Area beaches will experience hazardous conditions beginning Monday, December 7 and ending on Tuesday, December 8.

“Infrequent yet dangerous sneaker waves are expected,” reads the advisory. “For the High Surf Warning, dangerously large breaking waves of 25 feet at west to northwest beaches tonight through Tuesday. Enhanced coastal run up, localized beach erosion, and stronger rip currents are expected both today and Tuesday,” the National Weather Service stated.

The advisory explained that key areas to avoid will be “at west to northwest facings beaches along the entire coastline from Sonoma county southward through Big Sur in Monterey county. The Northern Monterey Bay (including Santa Cruz) will face a lesser threat due to this area being sheltered from northwest seas, however, there will still be an increased risk of sneaker waves, rip currents, and larger wave runup.”

The National Weather Service explains that sneaker waves can be deadly, and people should avoid going into the ocean when advised.

“Sneaker waves are deadly, larger-than-average swells that can suddenly and without warning surge dozens of feet higher up the beach than expected, overtaking the unwary. They can break over rocks and lift logs on the beach with deadly force. Individuals caught in the path of these deadly waves can wind up being pulled off the beach into frigid water and swift, ocean currents,” the National Weather Service stated.

“Sneaker waves strike people who seriously underestimated the risk they are in. They are called sneaker waves because they often appear with no warning after long periods of quiet surf and much smaller waves, lulls that can last for 10 to 20 minutes,” added the National Weather Service.

This can lull a beachgoer into thinking that the beach is safe. The National Weather Service indicates that the surge of a sneaker wave can go more than 150 feet up the beach. Beachgoers can be rendered powerless because of a sudden surge of cold, frigid water bringing a “watery mixture of sand and gravel” getting inside clothes and weighing someone down like cement, the National Weather Service mentioned.

“If you must visit the coastline, avoid venturing out on coastal rocks, outcroppings, jetties, etc, and remain extremely vigilant of your surroundings at all times,” states the National Weather Service.