Keaau, HI 96749 Weather

Synopsis

High pressure far north of the Hawaiian islands will maintain a moderate to locally windy trade wind pattern over the region into the middle of the week. Moderate trades and fewer showers are expected during the second half of the week, with an increase in shower this weekend.

Discussion

No change to the forecast this morning. A high pressure ridge remains to the north of the islands, maintaining a moderate to locally windy trade wind pattern over the region. Isolated areas are likely to flirt with advisory level winds today, with a downward trend in the winds over the next 24 hours.

Passing showers will continued to be carried in on the trade wind flow today, with showers focused over the windward and mauka areas. Satellite derived precipitable water (PW) shows a drier than normal airmass upstream of the islands. Expecting shower activity to taper off overnight, with isolated shower activity expected then through Friday.

Good model agreement continues between the ECMWF and GFS models that the high mentioned above will weaken Wednesday as a strong low, currently about 2500 miles to the northwest, moves to the east and sets up far north of the islands Thursday. The low is forecasted to deepen into the weekend, with an associated front then moving towards the islands over the weekend. Currently both global models are in good agreement with showers increasing over the northern islands first on Saturday, with showers spreading to the central islands as the front dissipates.

An increase in dewpoints is expected during the second half of the weekend and into the early part of the new week, which will bring warm and humid conditions back to the islands.

There are wide differences in the ECMWF and GFS as we head into next week. The GFS wants to develop a low near 15N180 and move it to the northeast, approaching the Hawaiian islands from the west before it turns to the north. This solution does bring the possibility of some heavier rain, however the latest ECMWF doesn't indicate this. As such not putting a lot of weight into either solution this far out.

Aviation

Another day of breezy trades expected today. A few isolated showers are possible for windward and mauka areas, which could lead to brief periods of MVFR cigs/vis. Trades look to weaken a bit near the end of the forecast period.

AIRMET Tango remains in effect for tempo moderate turbulence downwind of terrain below flight level 090.

Marine

High pressure far north of Hawaii will maintain fresh to strong trade winds through tonight, and a Small Craft Advisory (SCA) remains in effect for all waters except windward Big Island through tonight. Trades will steadily decrease early Wednesday as the high weakens and is displaced eastward by an approaching low far northwest of the islands. The SCA will likely be trimmed back to the typically windy waters around Big Island and Maui at that time. Trade winds will lower to gentle strength, or may become disrupted entirely, as the low passes to the north Thursday and Friday. Trades could then turn more northeasterly this weekend, and model discrepancies exist regarding a potential trough moving in from the southwest which could affect wind speeds.

For north facing shores, expect tiny surf over the next few days before a small northwest swell arrives giving a small bump on Thursday and Friday. This will then be followed by a slightly larger mid period north- northwest swell this weekend. A potential storm force low in the process of developing north of Japan could send a larger long period west- northwest swell early next week, bringing surf up to just below advisory (15 feet) levels. This swell is still uncertain and will depend on the evolution of the developing low.

Small background south swells will keep relatively small surf for south facing shores through much of the week. A moderate south- southwest swell is expected this weekend, and could bring surf heights above seasonal averages.

Rough trade wind swell will gradually decline later tomorrow morning as trade winds decrease, leading to smaller surf through the remainder of the week. A small medium period east swell is possible Thursday into the weekend.