SATELLITE DISCUSSION

Synopsis

Moderate trade winds will prevail state-wide into Friday. Stable and rather dry conditions will persist over most areas, with an increase in windward rainfall expected on the Big Island and Maui early Friday. Winds will shift out of the southeast over the western end of the island chain late Friday and Saturday as a front approaches. The dissipating front will likely fuel increased showers over portions of the state during the first part of next week, while high pressure setting up northwest of the state drives breezy and gusty trade winds over all islands.

Discussion

A stable and rather dry trade wind flow dominates this afternoon. A relatively weak surface high is passing about 350 miles northeast of the islands, while ridging aloft remains in place overhead. A diffuse band of scattered to broken cumulus clouds has persisted over and east of Kauai, but not much rain has fallen from this feature, since the afternoon Lihue sounding showed the inversion at 4500 ft with precipitable water less than an inch. The atmosphere is very dry across the rest of the island chain, where the inversion is closer to 3500 ft and precipitable water is just over a half an inch according to the Hilo sounding. A stable and rather dry trade wind flow will continue to dominate over most of the state through Friday. Shower chances will continue to be slightly higher across windward Kauai as the above mentioned band lingers through the evening. An area of moisture currently sitting 225 miles east of Hilo will drift westward overnight, bringing an increase in windward rainfall on the Big Island and east Maui late tonight or Friday morning. Rainfall should be minimal elsewhere. Heading into the weekend, the surface ridge north of the state will strengthen and edge a little closer to the islands. As a result, easterly trade winds over the Big Island and Maui will continue, and could possibly strengthen a notch, while winds shift out of the southeast over Kauai and Oahu. Rainfall will continue to be focused over windward slopes of all islands, but a hybrid trade wind and sea breeze pattern over the smaller islands could produce clouds and a slight chance of afternoon showers over leeward areas. An increase in trade winds and periods of active showers on some islands are expected during the first half of next week. Strong high pressure building far northwest of the state will push a dissipating frontal boundary toward the islands on Monday. An increase in rainfall is due on Kauai by Monday night, with the band of moisture possibly moving over Oahu and parts of Maui county on Tuesday. The latest GFS and ECMWF guidance shows that trade winds will become breezy and gusty on Tuesday and Wednesday, though its too early for details.

Aviation

Vfr conditions prevail at all taf sites and these conditions are expected to continue through the night. There may be some brief MVFR conditions over E and NE facing slopes on Kauai and possibly over Oahu overnight as moisture riding in on the trades interacts with island terrain.

Marine

Buoys 51001 and 51101 to the northwest of the state have shown a slow downward trend in the northwest swell during the past few hours, mainly in the 12 to 14 ft at 14 to 15 seconds range. Giving these readings, the high surf warning for most north and west facing shores from Kauai to Maui has been extended through the night, while west facing shores of the Big Island have been taken down to a high surf advisory. The warning will likely be replaced by a high surf advisory for most of the affected areas on the smaller islands for Friday. The next northwest swell is expected to produce advisory level surf on Sunday and Monday. A small craft advisory /sca/ remains in effect for most waters due to elevated seas from the large swell, and a SCA goes into effect tonight for locally strong trade winds across the typically windy waters around the Big Island and Maui. Winds will remain at border line strength in the affected areas for Friday and Saturday, while the areas affected solely by elevated seas will briefly drop out of the SCA. Another northwest swell will produce hazardous seas on Sunday. Stronger trade winds are expected on the Monday holiday. The winds, and shower activity, will likely increase first around Kauai, then spread down the island chain for Tuesday into Wednesday.

HFO Watches/Warnings/Advisories

High surf warning until 6 am HST Friday for north and west facing shores of Niihau Kauai Oahu and Molokai, and for north facing shores of Maui. High surf advisory until 6 am HST Friday for west and north facing shores of the Big Island. Small craft advisory until 6 pm 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. Small craft advisory from 6 pm this evening to 6 pm HST Friday for Maalaea Bay, Pailolo channel, Big Island southeast waters.

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