The National Weather Service has extended a high surf advisory for Oahu, Kauai and Maui counties as waves to 15- to 20-feet, with higher sets, pound north shores.

The surf is expected to diminish tonight to 10- to 14-feet Saturday.

West shores are seeing 10- to 14-foot waves, lowering to 6- to 10-feet Saturday.

North Shore lifeguards warn that swimmers and surfers shouldn’t overestimate their abilities and should leave the big surf to experts.

The National Weather Service said the surf can created strong breaking waves, significant shore break and strong rip currents making swimming dangerous.

On Kauai, county officials at the Ocean Safety Bureau closed all beaches north of the Hanalei pavilion from Hanalei to Kee.

The advisory affects north and west shores of Oahu and Kauai County and north shores of Maui and Molokai.

Honolulu fire officials reported coming to the aid of a bodyboarder at Waimea Bay just after 7:30 a.m. and a swimmer at Turle Bay around 11:30 a.m. Friday.

Capt. James Todd, Honolulu Fire Department spokesman, said the bodyboarder needed help getting back to the beach.

Capt. John Hogsteden, North Shore Ocean Safety official, said “surfing conditions along the North Shore are very good.”

Along with Vans Triple Crown of Surfing competition at Sunset Beach, North Shore beaches are extremely busy, both ocean safety and fire officials said.

Hogsteden said swimmers and surfers have to be realistic making sure that “the surf they are getting into isn’t over their ability level.”

“The big thing today is prevention,” he added.

“Boaters should be aware of an increased number of surfers and body boarders utilizing the harbor channel to access surfing areas,” the weather service said in an advisory message. “Heed advice from ocean safety officials and exercise caution.”