A high surf warning has been issued for the north and west shores of most Hawaiian isles, effective through 6 p.m. Friday.

The National Weather Service expects a large, northwest swell to rapidly build down the island chain today.

“This large swell will likely adversely impact coastal areas, especially during Thursday and Friday evening high tide times,” said the warning. “Preparations should be made for significant coastal impacts as ocean water runs up and inundates beaches and potentially affects coastal properties and roadways.”

>> Surf of 35 to 45 feet is expected along most north shores, including Niihau, Kauai, Oahu, Molokai and Maui.

>> Surf of 20 to 25 feet is expected along most west shores, except Maui.

>> On Hawaii island, surf of 15 to 25 feet is expected along north shores, and surf of 8 to 12 feet along west shores.

The highest surf is expected to affect Kauai this morning through Friday; on Oahu, from this afternoon through Friday; on Maui, from later this afternoon through Friday; and on Hawaii island, from this evening through Friday.

The impacts will be very high, with ocean water surging and sweeping across beaches, and powerful longshore and rip currents present at most beaches.

The public should stay away from the shoreline along affected coasts, be prepared for road closures, and postpone entering or leaving channels affected by the high surf until it subsides.