Warning-level surf will continue Thursday for north and west shores but will gradually decline through the day, the National Weather Service forecasts.

The surf is expected to top out at 20 feet to 30 feet on north-facing shores, and 12 feet to 18 feet on west shores.

A high surf warning is in effect for north- and west-facing shores along Oahu, Kauai, Molokai, and Niihau; Maui’s north-facing shores; and Hawaii island’s west-facing shores.

A high surf advisory is in effect for Oahu’s south-facing shores as well as west-facing shores along Maui, Lanai and Kahoolawe.  

Surf at some Oahu south shores that experienced the swell’s wrap-around effect on Wednesday, which brought surf ranging from 6 feet to 10 feet, will see waves drop to 4 feet to 8 feet on Thursday — the low end of the advisory criteria.

“We’re not expecting the surf to drop below advisory levels,” said Anthony Reynes, meteorologist with the Weather Service Wednesday night. “Likely warning levels will be followed by advisory levels on Friday.”

Reynes described it as a “pretty big, long-period swell,” which was producing  through Wednesday night very large surf — between 30 to 40 feet on north shores, and 15- to 25-foot surf on the west-facing shores.