A high surf advisory has been issued for north and west shores of all isles from Niihau to Molokai, and north shores of Maui due to a large, northwest swell, in effect through 6 a.m. Thursday.

The National Weather Service said surf is expected to build to 15 to 20 feet this afternoon, and then ramp up to 18 to 24 feet tonight along north shores.

Surf along west shores is expected to build to 14 to 18 feet tonight.

Although impacts are moderate, officials warn of strong, breaking waves and rip currents, making swimming difficult and dangerous.

The forecast, meanwhile, is mostly sunny this morning, and partly cloudy in the afternoon, with scattered showers for Kauai, and highs from 82 to 87 degrees Fahrenheit. Lows tonight dip to 69 to 74 degrees.

Trades remain variable up to 15 mph but increase to 20 mph tonight through Thursday, and will become breezy for Christmas Day on Friday.

Forecasters say the large, northwest swell that prompted today’s high surf advisory peaks tonight into Thursday morning, when surf on north shores reaches 18 to 23 feet before starting to subside.

Another northwest swell, however, is expected to arrive Thursday night into Christmas Day on Friday, which will likely extend the high surf advisory.

Surf for south shores is also expected to rise from 4 to 6 feet today to 6 to 8 feet Thursday due to a new, out-of-season south swell filling in today.

Surf on east shores is forecast to remain at 1 to 3 feet today and Thursday.

A small craft advisory has been issued for Kauai northwest, windward and leeward waters due to the northwest swell, in effect from 2 p.m. today through 6 p.m. Thursday.