With surf expected to build to 40 to 50 feet today along the north shores of most isles, a surf competition is also gearing up at Pipeline on Oahu’s North Shore.

Da Hui Backdoor Shootout kicked off Dec. 30 and has been in a waiting period since the start of the year.

The competition honoring surf legend Duke Ka­hanamoku draws Hawaii’s top watermen — including defending champion Koa Rothman, Makua Rothman, Jamie O’Brien, Kealii Mamala, John John Florence and Mason Ho — to surf their best at Backdoor, Pipeline and Off the Wall.

The National Weather Service has extended a high-surf warning for the north and west shores of Niihau, Kauai, Oahu and Molokai, and for the north-facing shores of Maui, until 6 p.m. Sunday.

Surf in the 40- to 50-foot range is expected for the north shores of Oahu, Molokai, Maui and Hawaii island, and the north and west shores of Kauai and Niihau, the weather service said. The west shores of Oahu and Molokai can anticipate surf of 25 to 35 feet.

Lifeguards on Friday made 12 rescues and 1,575 preventive actions on the North Shore, and four rescues and 820 preventive actions along the Waianae Coast, the city said.

A high-surf advisory remains in effect for the north-facing shores of Hawaii island through 6 p.m. Sunday. Surf in the 12- to 16-foot range is forecast for the west shores of Hawaii island, and 20 to 30 feet for the shore from Hilo to Hawi.