SATELLITE DISCUSSION

Synopsis

Light trade winds will gradually strengthen on Thursday, but dry and cool weather will continue overnight. Moderate trade winds will then continue into the weekend, delivering clouds and a few showers to windward areas, mainly on Friday and Saturday. However, a stable atmosphere will limit shower coverage and intensity. An approaching front will cause winds to weaken and shift to the southeast on Saturday and Sunday. Strong high pressure passing north of the islands early next week will bring gusty trade winds, and moisture associated with the dissipating front is expected to fuel a wet trade wind flow from Monday night into Wednesday.

Discussion

A broken to overcast band of showery low clouds just N of Kauai marks the remnants of a stalling and dissipating front, while an e- W oriented surface ridge over the islands is keeping island winds light, and skies clear over surrounding waters. The light large- scale winds have allowed sea breezes to drive cloud formation over island interiors and lower slopes this afternoon, but showers have not been observed due to the dry and stable air mass that has persisted in the wake of this past weekend's frontal passage. Forecast models indicate that a gradually strengthening high pressure cell will pass N of the islands tonight, and move steadily E through Friday before settling in far NE of the islands on Saturday. This will lead to the surface ridge temporarily moving N of the islands, with gentle to moderate trade winds developing over in response. The trade winds are expected to persist into Saturday, but a front approaching from the NW will weaken the W end of the ridge, and winds will gradually weaken and veer to the SE on Saturday and Sunday, with this effect first being felt on Kauai. Dew point temperatures are expected to steadily increase through Sunday as the air mass gradually warms and moistens. Although Thursday morning will still be chilly by island standards, temperatures thereafter will be steadily recovering from the recent chill. By late Sunday and Monday, relatively strong high pressure developing NW of the islands will lead to an increase in NE trade wind speeds. As the high tracks E, moisture associated with the dissipated front is forecast to become embedded in the strong trade wind flow, bringing a fairly wet trade wind pattern. Latest model data indicate that the e-w oriented moisture axis will move over Kauai Monday night and Tuesday, Oahu Tuesday night, and Maui county and Hawaii Wednesday and Wednesday night, fueling numerous trade wind showers. Worth noting however that there have been run-to- run and model-to-model differences with respect to the timing and strength of the moisture axis, but a fair amount of agreement in the fact that strong trade winds will punctuate the island weather pattern early next week. Therefore there is greater confidence in the wind forecast as opposed to the rainfall forecast.

Aviation

Clouds along interior areas will scatter out this evening and light to moderate trade winds will begin to return tonight. Conditions throughout the state should remain fairly quiet with minimal shower activity expected. The highest chance for showers will be near Kauai as a weakening front dips closer to the state. There are no airmets in effect, and none are expect through the period.

Marine

A much anticipated large NNW swell is producing dangerously large surf this afternoon along exposed N and W facing shores. Although the swell arrived later than expected, it is now about as big as originally forecast, and powerful surf is pounding island shorelines. The Oahu surf discussion /srdhfo/ has been updated this afternoon and can be referenced for additional details regarding this swell. The swell will gradually subside Thursday night into Friday, and should drop below the high surf advisory criteria by late Friday. A WNW swell expected Sunday will likely produce surf reaching the high surf advisory criteria along most N and W facing shores of the smaller islands through Monday. The W component of this swell may also produce advisory level surf along the W facing shores of the Big Island from late Sunday into Monday. A small craft advisory /sca/ remains in effect through Thursday night for most Hawaiian waters due to the elevated seas associated with the large NNW swell. The strengthening trades may cause wind speeds to increase to the SCA criteria in the typically windy waters adjacent to the Big Island and the islands of Maui county Thursday night.

HFO Watches/Warnings/Advisories

High surf warning until 6 pm HST Thursday for north and west facing shores of Niihau Kauai Oahu Molokai and for north facing shores of Maui and for west facing shores of the Big Island. High surf advisory until 6 pm HST Thursday for north facing shores of the Big Island. Small craft advisory until 6 am HST Friday for Kauai northwest waters, Kauai windward waters, Kauai leeward waters, Kauai channel, Oahu windward waters, Oahu leeward waters, Kaiwi Channel, Maui county windward waters, Alenuihaha channel, Big Island windward waters.

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DISCUSSION/MARINE...BIRCHARD AVIATION...EATON

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