A high surf advisory has been issued for north and west shores of most isles, starting tonight.

The National Weather Service warns of a long-building, northwest swell, which is expected to deliver advisory-level surf to the north and west shores of Niihau, Kauai, Oahu and Molokai and north shores of Maui and Hawaii island tonight through Thursday.

The advisory for all except Hawaii island is in effect through 6 p.m. Thursday. The advisory for Hawaii island is scheduled to go into effect at 6 p.m. today and run through 6 p.m. Thursday.

The swell will continue to build today, reaching 12 to 16 feet along the north and west shores of the smaller islands and 8 to 12 feet along the west shores of Oahu and Molokai, forecasters said.

Expect surf to reach 12 to 16 feet along the north-facing shores of Hawaii island tonight. The swell is expected to peak near warning levels Thursday into Thursday night.

A slight chance of thunderstorms and heavy rainfall is also forecast for Kauai for the rest of today, as well as for the Kona slopes of the Hawaii island this afternoon and islandwide Thursday afternoon.