A high surf warning is in effect for the north and west shores of Oahu and Kauai County through 6 p.m. today.

A large northwest swell is expected to spread down the island chain today, bringing warning-level surf to Oahu, Kauai and Niihau, according to the National Weather Service.

The swell will also bring advisory-level surf to the north and west shores of Molokai, the north-facing shores of Maui and portions of the Big Island’s leeward coast.

The swell will peak today, followed by a gradual decline through Friday.

Surf is building to 25 to 30 feet this morning for Kauai County warning areas, 20 to 25 feet for the north, and 15 to 20 feet for west-facing shores of Oahu.

Officials warn of ocean water sweeping across portions of beaches at times, in addition to very strong, breaking waves and rip currents. Breaking waves may also affect harbors, making navigating the harbor channel dangerous.

Beachgoers, swimmers and surfers should exercise caution and heed all advice given by ocean safety officials.

Forecasters, meanwhile, expect a showery and breezy tradewind pattern to continue through the weekend. Showers will be most prevalent over windward and mauka areas, with a few spilling over into the leeward side.

Today’s highs are from 82 to 87 degrees Fahrenheit, with east winds of 15 to 25 miles per hour. Tonight’s lows are from 71 to 76 degrees.

Developing tradewinds today are expected to increase to windy conditions tonight through Sunday. The trades are expected to peak some time between Friday to Sunday, and may require wind advisories for parts of Big Island and Maui County.

A small craft advisory has also been issued for waters from Kauai to the Big Island, effective through 6 p.m. Friday due to the northwest swell, combined with strong trades that are expected to near gale force by Friday in some channels.