Surfers and wave-watching tourists enjoyed a building northwest swell Friday afternoon on Oahu.

Lifeguards reported no major rescues from the 10 to 15 foot waves.

Surf is expected to build to 15 to 20 feet overnight into Saturday.

The National Weather Service has issued a high surf advisory until 6 p.m. Saturday because of the threat from dangerous rip currents generated by the big waves.

The advisory is for north and west shores on Oahu, Kauai, Molokai and Niihau and for the north shore of Maui.

Surf on west shores is predicted to be in the 10 to 15 foot range.

The swell is expected to peak on Saturday and slowly decrease through Sunday.

Forecasters say a reinforcement swell may bring moderate surf Monday and Tuesday on north and west shores.

South shores could also see a small bump Monday and Tuesday from a storm near New Zealand last week.