Hawaii North Shore forecast by Craig Brokensha (issued Mon 15th December)

Photo by Matt Dunbar

Best Days: Thursday through Sunday for experienced surfers

This week and Saturday (Dec 16- 20)

After the weekend's large pulse of NW groundswell which saw Pipe apparently offer one of the best sessions this season Saturday afternoon (right), wave heights have dropped away and the swell has swung more northerly with stronger E/NE trades into today.

We should continue to see the swell drop out from the N'th tomorrow from 3-5ft across exposed breaks as fresh E'lyt trades slowly back off and become lightest into Wednesday morning. More than likely another lay day for the Pipe Masters.

Only a slight lift in new NW groundswell is due through the day Wednesday, peaking Thursday morning to 3-5ft across the North Shore ahead of a larger and better NW groundswell late in the day.

The origins of this NW groundswell will be a deepening low pressure system to Hawaii's north-west during the coming days with a fetch of severe-gale to storm-force winds forecast to be aimed towards the islands as the low pushes east (pictured below right).

A large long-period NW groundswell should result, building later Thursday to 6-8ft+ by dark and then peaking Friday morning to 10-12ft across swell magnets on the North Shore, 8-10ft at Pipe.

A steady drop in size is due through the day and further Saturday as the swell swings a touch more north.

Winds look to strengthen again into later Wednesday and remain fresh to strong from the E/NE Thursday and then ease off slowly Friday while swinging a touch more E. Saturday as the swell eases from the 6ft to occasionally 8ft range across exposed breaks should see favourable and weaker E/SE winds ahead of afternoon sea breezes. This could see the Pipe Masters run on any of these days, but Friday morning (early Saturday Australian time) will be the one to watch with the large easing swell.

Sunday onwards (Dec 21 onwards)

A very large and powerful groundswell due Sunday afternoon/evening is still on track but there's been a few changes that have gone against it coming in at the XXL size.

Over the coming 24-36 hours a low pressure system moving over Japan is expected to 'bomb,' dropping over 24hPa in central pressure in less than 24 hours.

Unfortunately it will expend most of its energy while sitting over Japan reducing the fetch of severe-gale to storm-force winds being aimed towards Hawaii but while also splitting it in two latitudinally owing to the interaction of the low with the Japanese Alps.

This will mean the strongest winds will be generated in Hawaii's far swell western swell window before the low slowly starts pushing east towards the islands while weakening.

What we're now expecting through Sunday is the arrival of a very inconsistent long-range W/NW groundswell during the morning, building strongly to a large 15-20ft by the evening across exposed breaks on the North Shore. A peak is due overnight ahead of a drop from a similar size Monday morning but good light to moderate E/NE trades Sunday will go poor and strong from the N/NE into Monday.

Longer term another large reinforcing NW groundswell is due into Tuesday/Wednesday but with terrible winds from the N'th tending NW. More on this Thursday though.

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