FORECAST DISCUSSION

Synopsis

High pressure east-northeast of the state will keep mainly moderate to fresh trade winds through Thursday. Winds will become locally light and variable Thursday night and Friday as a front approaches from the northwest. The front will advance across the smaller islands over the weekend, then stall near the Big Island early next week, with increasing showers across the state. Additionally, very strong trade winds are expected for the state this weekend, before easing early next week.

Discussion

Trade wind weather continues across the islands this evening as a high pressure remains far east-northeast of the area. There are some low clouds in the island vicinity. These clouds are not bringing much, if any, precipitation as air mass stays rather dry and stable as depicted by earlier afternoon soundings. Latest satellite imagery does show some more low clouds just upstream east of the islands, but then as weather conditions remain unfavorable for rainfall development, hence expect mainly fair weather to prevail across the state through rest of the evening into early Thursday morning. The high far east-northeast will move further east on Thursday, while a cold front far northwest of area will advance closer to the islands. This will result in the gradual weakening of trade winds later on Thursday. Nevertheless, still expect mainly trade wind weather on Thursday, with passing low clouds and showers affecting mainly windward and mountain areas. Rainfall amounts will remain low as airmass will still be stable. Lighter synoptic winds by Thursday night and Friday will allow more widespread localized nighttime land breezes and daytime sea breezes to develop over the islands. Furthermore, weather may become a little more convective, with clouds developing over the daytime and some clearing at time. Once again, precipitation will be limited due to stable weather pattern. Northeast winds will dramatically increase late Friday night into Saturday as the cold front sags near the state with a strong high builds far north behind the front. The strong pressure gradient will develop across the area, resulting in very windy trade winds for the islands through the weekend. Winds will likely be strong enough to reach advisory levels for all or portions of the state. Along with the winds, an increase in showers is expected. Showers will be most prevalent across windward and mauka areas, but with the increasing trades and rising inversion heights, some of the showers will reach leeward areas of the smaller islands as well. The front is still expected to stall near the Big Island early next week with winds veering east. Winds will turn more southeast and becoming light across the state as another front is forecast to approach the islands from the northwest. Both long range GFS and old ECMWF still keep much of the moisture associated with this front just north to northeast of the state as it passes the area late Monday into Tuesday.

Aviation

High pressure northeast of the state will keep a light to moderate trade wind flow in place, with clouds and very light showers affecting mainly windward and mauka areas. Brief MVFR cigs will be possible in windward areas, but predominantly VFR conditions are expected through Thursday. AIRMET Tango remains in effect for low level turbulence over and downwind of the terrain. These conditions are expected to remain in place through the night.

Marine

The new west-northwest swell is expected to peak late tonight and early Thursday, then lower gradually later Thursday and Thursday night. With the more westerly direction of this swell, high surf will also reach west-facing shores of The Big Island later tonight and Thursday. Another large northwest swell is expected to arrive Thursday night and Friday with advisory level surf expected. This swell will lower gradually over the weekend. A short period north- northeast swell is expected over the weekend behind a cold front moving across the area. The swell will gradually swing around to the east early next week. Advisory level surf is likely along north and east facing shores with this new swell. Another large northwest swell is expected for next Tuesday and Wednesday. A Small Craft Advisory is presently posted for most Hawaiian coastal waters, mainly due to seas associated with the new west- northwest swell. Winds around portions of The Big Island are also reaching Small Craft Advisory levels. (However, winds are expected to drop off later tonight and Thursday.) Winds behind a cold front moving across the chain this weekend will exceed advisory criteria and could reach Gale Warning levels across some areas. Also, seas will remain rather high through the weekend and into early next week.

HFO Watches/Warnings/Advisories

High Surf Warning until 6 PM HST Thursday for north and west facing shores of Niihau, Kauai, for north facing shores of Oahu, Molokai and Maui, and for west facing shores of the Big Island. High Surf Advisory until 6 PM HST Thursday for west facing shores of Oahu. Small Craft Advisory until 6 PM HST Thursday for all Hawaiian waters except Maalaea Bay

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AVIATION...Jelsema MARINE...Kinel REST...Hui

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