A third swell this week has prompted the National Weather Service to extend a high surf advisory for north and west shores of Oahu, Molokai, Kauai and Niihau, north shores of Maui and the Big Island until 6 p.m. Monday.

Waves of 15 to 20 feet are expected on north shores today. The swell is forecast to peak on Sunday, when a high surf warning may be issued as waves rise to  25 to 30 feet.

Surf has been at advisory levels since Christmas Eve when the first of three swells arrived.

Surf along west facing shores will rise to 10 to 15 feet today, the weather service said.

"The swell will produce hazardous surf and beach conditions tomorrow through Monday afternoon," forecasters said. "Expect ocean water occasionally sweeping across portions of beaches, very strong breaking waves and strong rip currents."

The state Department of Land and Natural Resources is also warning of dangerous conditions near Sunset Beach as the high surf is causing erosion and  debris, concrete,  trees and boulders are washing ashore.

"We are advising the public to avoid the area starting from the western-most side of Sunset Beach Park to Rocky Point area during this period of high surf," said William J. Aila, Jr., the DNLR chairman. "

We observed wood debris, concrete, trees, and boulders rolling in the surf and strewn out across the sand.  We want to let the public know to avoid the area because it is unsafe."  said administrator Sam Lemmo.  " We recommend the public and affected homeowners continue to avoid the area until the swell subsides."