The National Weather Service has issued a high-surf advisory effective through 6 p.m. today for Niihau, Kauai, Oahu, Molokai and Maui in anticipation of surf along north- and west-facing shores building overnight to 15 to 20 feet this morning.

The weather service issued the advisory Friday afternoon in response to a large northwest swell that was expected to produce hazardous surf along the north- and west-facing shores of Niihau and Kauai and the north-facing shores of Oahu, Molokai and Maui.

The high surf is expected to peak early this morning before gradually subsiding.

Forecasters warn that large-breaking waves could produce rough surf conditions and life-threatening rip currents. The public is advised to stay away from the shorelines of affected coastal areas.

City Emergency Services spokes­woman Shayne Enright said Ocean Safety personnel did not encounter any significant incidents related to the surf Friday, but will remain vigilant as conditions continue to develop.

A small-craft advisory is also in effect for Hawaii coastal waters within 40 nautical miles through 6 p.m. today.

Meanwhile, the weather service said an east-west surface ridge over the main Hawaiian Islands will continue to strengthen as it moves north this weekend. Locally heavy showers were expected on Oahu and Kauai on Friday night, with heavy showers persisting over waters west and north of Kauai today.

The weather service said that as the surface ridge moves north, tradewinds will return to Hawaii island and Kauai, clearing lingering vog over the weekend. The returning trades, reaching 10 to 20 mph, will bring windward showers in the morning and evening, the service predicted.

Global models indicate that a trough aloft and associated surface front approaching the main Hawaiian Islands from the northwest late next week will result in weakening trades and a return of voggy conditions.