The season’s biggest surf event is expected to slam area beaches this week and last into the weekend, creating dangerous conditions along the shore, the National Weather Service said Monday.

The NWS office in Oxnard issued a high surf advisory and a hazardous weather outlook because of the strong surf, which was expected to hit Monday night and last through today.

A second round of bigger waves is expected to roll in beginning Thursday night and last through the weekend, meteorologist Kathy Hoxsie said, adding that the system might bring some rain.

“It’s going to be pretty big,” she said. “We’re expecting up to 20-foot waves coming in, and it’s going to be around for a while.”

The waves are being generated by storms moving down from the Gulf of Alaska that are rolling over Northern California, Hoxsie said. One of the storms expected later in the week should stay to the north of Los Angeles, but it will be followed by a cold air mass that will produce strong winds with some gusts in the mid-30 mile per hour range, she said.

The biggest surf will be along the Central Coast but sets of 6 feet to 12 feet are expected along west facing beaches of Los Angeles and Ventura counties, the weather service said.

“These surf conditions will produce dangerous rip currents, minor coastal flooding and beach erosion, as well as sneaker waves that can inundate beaches and overtop jetties and rock walls,” the surf advisory said.

“Inexperienced swimmers and surfers should stay out of the water. Also, keep at a safe distance from the surf, stay off of rock walls and jetties and never turn your back on the ocean.”

Daytime temperatures today are expected to be in the high 70s to low 80s with a cooling trend starting on Wednesday, Hoxsie said.

There is a 30 percent chance of rain on Thursday afternoon, and by Friday daytime temperatures will have fallen into the mid-60s.

Spencer Parker, spokesman for the Los Angeles County Fire Department’s Lifeguard Division, said the gusty winds that will rake the Pacific Ocean during the period of high surf probably won’t be conducive to big wave riding. But there will be lifeguards on duty with jet skis and the rescue boats will be staffed, he said.

And the division does have a plan in place to increase lifeguard staffing if necessary.

“Once it gets closer to the weekend, we can get a really good read on what the swells are doing,” he said. “We have a lot of lifeguards that are part-time and on call. They make themselves available, and we can call them and tell them what lifeguard tower they are needed at.”

The west-facing beaches that will see the biggest surf are Manhattan Beach, especially the El Porto section, Venice and Zuma, officials said.

The other beaches in the county, while not getting a frontal hit from the surf, will experience an impact, said county Fire Department spokeswoman Lidia Barillas.

“The other beaches will also have some hazardous conditions as well,” she said. “And not all the towers are open so we really want to stress to the public to swim in front of an open lifeguard tower and come and talk to the guards. They can direct you to the safest place to swim.”