A high surf advisory is posted from 6 a.m Saturday to 6 p.m. Sunday as waves of 15 to 20 feet are expected on north shores of most islands.

The surf is expected to rise overnight on north and west shores of Oahu, Kauai, Niihau and Molokai, and on north shores of Maui and Hawaii island.

Surf along west shores is expected to reach 8 to 12 feet today from a combination of northwest swells.

"The swell will produce large and hazardous surf this weekend. The mixed direction and surf heights will create chaotic and unpredictable surf conditions," the weather service said. "Expect strong breaking waves, shore break and strong longshore and rip currents making swimming difficult and dangerous."

The swell should reach "dangerous levels" by Saturday afternoon, forecasters said. "Beachgoers, swimmers and surfers should heed all advice given by ocean safety officials and exercise caution. "

The swell is expected to peak tonight and decline into Sunday. But surf will continue to be near advisory levels on Monday and Tuesday as another swell from the northwest arrives.