The National Weather Service issued a high surf warning at 3:40 p.m. today for the north- and east-facing shores of Oahu, Hawaii island, Maui, Kauai, Molokai, and Niihau.
The warning is in effect until 6 a.m. Friday.
Weather officials say a large north swell will build through Wednesday, peak on Thursday, then decline Thursday night and Friday.
Surf is expected to rise 20 to 30 feet along north-facing shores and 10 to 15 feet along east-facing shores of the islands.
Ocean water is expected to occasionally sweep across portions of beaches and impact harbors, making navigating the harbor channel dangerous.
Boaters should be aware of an increased number of surfers and body boarders using the harbor channel to access surfing areas.