A large northwest swell peaked, but started to gradually decline late Sunday afternoon. 

The National Weather Service issued a high-surf warning for north- and west-facing shores of Oahu, Kauai, Molokai and Niihau and the north shore of Maui through 6 p.m. Sunday night. A high surf advisory is in effect for the west-facing shores of the Big Island.

Warning-level surf of 20- to 30-feet is rolling in to the north shores and surf on west shores peaked at 14 to 18 feet Sunday.

Forecasters say the dangerous surf conditions mean that only highly experienced swimmers should enter the water.

The north shore waves lowered Sunday afternoon, but will remain at advisory levels through Monday.

There were no reports overnight of debris or erosion from the waves, according to emergency management officials. 

A new, large swell, perhaps the biggest in years, is forecast to arrive either Tuesday through or Wednesday, bringing more warning-level waves.