High surf warning likely this weekend along Big Island western shores with arrival of extra-large swell

An extra-large swell moving into the state from the west-northwest to northwest will rapidly build Saturday night and peak during the day Sunday.

Forecasters at the National Weather Service office in Honolulu have high confidence that the swell will lead to warning-level surf for west-facing shores of the Big Island by Saturday night and possibly through Monday.

Large breakers of 12 to 18 feet, with higher sets along select Kona shores, are predicted, especially around high tide, which will happen about noon Sunday.

Forerunners will arrive as early as late Saturday afternoon and build through the night, with peak wave heights forecast during the day Sunday.

Forecasters said Wednesday that swell heights will peak at 6 to 7 feet Sunday, with a peak swell period of 16 to 20 seconds.

Forecasters advise the public to keep an eye on the statewide surf forecast for the latest surf heights as the event nears.

The swell should begin to gradually decline Sunday afternoon and continue a downward trend through the middle of next week.

This is the first major winter swell of the season.

Elsewhere in the state, such as Kaua‘i, monster surf of 40 to 50 feet, with some even larger sets, is forecast along north-facing shores and huge breakers of 25 to 35 feet pounding western shorelines.

That could lead to coastal and harbor impacts for exposed northern and western shorelines, especially during high tides, which will move in near midnight and noon Saturday night and Sunday on the Garden Isle.

Ocean water will surge and sweep across beaches, creating the potential for impacts to coastal properties and infrastructure, including roadways.

There is moderate agreement that waves could wash across roads near shorelines exposed to the swell at high tide on those islands expected to see the gigantic breakers.

Powerful longshore and rip currents will be present at most Kaua‘i beaches as well.

Large breaking waves and strong currents could even impact harbor entrances and channels, causing boat handling to become challenging.