A high-surf warning began at 8 a.m. today for north and west shores of isles from Niihau to Hawaii island, and remains in effect through 6 p.m. Thursday.

The National Weather Service said a long-period, northwest swell will build to 15 to 25 feet this afternoon then peak to 25 to 35 feet tonight and early Thursday, with dangerously high levels, along north shores.

Surf for west shores is expected to reach 12 to 20 feet this afternoon, and 15 to 25 feet tonight.

The warning applies to north and west shores of isles from Niihau to Molokai, the north shores of Maui, and west shores of Hawaii island.

Officials warn of ocean water occasionally sweeping across beaches, very strong, breaking waves and rip currents. Breaking waves may occasionally impact harbors, making navigation of the harbor channel dangerous.

In addition, there will likely be long lulls between the sets of larger waves as the swell builds this afternoon. Larger waves can arrive suddenly, catching some off guard.

Entering the water in these areas is also very hazardous.

Today is expected to be mostly sunny, with clear skies, a few isolated showers and highs from 78 to 83 degrees Fahrenheit. Tradewinds, meanwhile, have eased to 5 to 15 miles per hour. Tonight’s lows are from 61 to 66 degrees.

Forecasters said a cold front north of the isle chain, and another front approaching from the northwest, will maintain dry weather, with light winds, through Friday. Stronger trades are expected to return on Friday, bringing scattered showers to windward and mauka areas of all isles through Sunday morning.

A small craft advisory for most waters, from northwest Kauai to southeast Big Island, also remains in effect through 6 p.m. Thursday.