Area Forecast Discussion for Hawaii

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Issued: Jan 19, 2017 4:00 AM HST

Synopsis
High pressure far east-northeast of the state will keep light to moderate trade winds today. Winds will become locally light and variable tonight and Friday as a front approaches from the northwest. This 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 early this morning as a high pressure remains far east-northeast of the area. Low clouds have filled in a bit along the windward coastal waters overnight and are bringing some showers mainly to windward and mountain areas. Early morning Lihue and Hilo soundings continue to depict a rather dry and stable airmass in the island vicinity. Therefore, rainfall amounts from these passing showers will be limited. The aforementioned high will move further east today, while a cold front far northwest of area will advance closer to the islands. This will result in the gradual weakening of trade winds throughout the day. Nevertheless, still expect mainly trade wind weather today, with passing low clouds and showers affecting mainly windward and mountain areas.

Lighter synoptic winds by tonight 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 during the day, then some clearing at night. Once again, precipitation will be limited due to the stable weather regime.

Northeast winds will dramatically increase late Friday night into Saturday as a cold front advances near the state, while a strong high builds far north behind the front. The strong pressure gradient expected to develop across the area will result in very windy trade winds for the islands through the weekend. Winds will likely be strong enough to reach advisory levels for at least 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. Strong winds will also keep showers moving rather swiftly across the area, limiting the rainfall accumulations somewhat.

The front is still expected to stall near the Big Island early next week with winds veering east. Winds will turn more southeast then becoming light across the state as another front is forecast to approach the islands from the northwest. Both long range GFS and ECMWF still keep bulk of the moisture associated with this next front just north to northeast of the state as the main frontal boundary passes northeast of the area Tuesday. The islands are expected to see moderate northerly winds briefly after this front exits east.

Aviation
High pressure northeast of the state will keep a light to moderate trade wind flow in place today, with winds diminishing tonight as a front approaches from the northwest. Predominantly VFR conditions are expected through tonight, with brief MVFR cigs in light showers or mist possible across mainly windward and mauka areas.

AIRMET Tango remains in effect for low level turbulence over and downwind of the terrain of all islands. Boundary layer winds are expected to diminish later this morning and the AIRMET will be cancelled when this occurs.

Marine
The west-northwest swell is expected to peak early today, then lower gradually later today and tonight. With the more westerly direction of this swell, high surf will also reach west- facing shores of The Big Island today. Another large northwest swell is expected to arrive tonight 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, though they are expected to drop off today. 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.

Watches/Warnings/Advisories
High Surf Warning until 6 PM HST this evening 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 this evening for west facing shores of Oahu.

Small Craft Advisory until 6 PM HST this evening for all Hawaiian waters except Maalaea Bay.


AVIATION...Jelsema

MARINE...Kinel

REST...Hui