A high surf advisory remains in effect for the north and west shores of Niihau and Kauai, and for the north shores of Oahu, Molokai and Maui, effective through 6 a.m. Friday.

The National Weather Service said surf of 12 to 15 feet is expected on affected shores due to a northwest swell that will peak today, then ease up through the weekend.

Short-period choppy surf is expected to continue along east shores, with advisory level surf once again expected Friday through Saturday due to strengthening tradewinds.

Expect strong breaking waves and rip currents, making swimming difficult and dangerous.

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

On the horizon, a high wind watch has been issued for all Hawaiian isles from Friday afternoon through Saturday afternoon.

A strong, high-pressure system will build north of the isles, officials said, bringing strong easterly trades that are expected to strengthen Friday and peak on Saturday.

East winds of 25 to 40 miles per hour, with gusts up to 60 mph are possible at various locations, including the shores, mountains and interiors of all isles, from Niihau to Hawaii island, including Saddle Road above 5,000 feet.

Officials warn that damaging wind gusts could blow down trees and power lines, leading to power outages. Travel could also be difficult, especially for high-profile vehicles crossing higher elevations. Winds can also be especially strong downwind of mountain tops and ridges, and through valleys and gaps in terrain.

Forecasters, meanwhile, say high clouds are expected to increase in coverage tonight, and remain in place over most of the state into the weekend.