000 FXHW60 PHFO 230154 AFDHFO Area Forecast Discussion National Weather Service Honolulu HI 354 PM HST Fri Feb 22 2019 .SYNOPSIS... A surface trough near the Big Island will support increased clouds and chances of showers over the eastern end of the island chain through the weekend. Meanwhile, weak high pressure to the northwest will support mostly dry weather over Kauai and Oahu. A cooler northerly flow is expected across the state next week. && .DISCUSSION... The Big Island remains in the vicinity of a weak surface trough. At the upper levels a zonal west to southwest flow is transporting the higher level clouds off to the east and northeast, while light winds at the surface are allowing sea breezes to dominate. The upper level jet has weakened enough to allow the winds to weaken on the Big Island summits below wind advisory levels. Wind speeds should remain below advisory tonight, but slight changes in the jet position and strength over the next few days may necessitate future wind advisories. Expecting continued showery conditions around the eastern side of Big Island into the evening. Instability is marginal for deep convection and a few heavy showers, but also can't rule out a slight chance for a thundershower in those same areas this evening. This overall pattern appears more or less locked in through early Sunday. An axis of higher humidity remains stuck near the Big Island, and occasional upper level shortwaves bringing potential bursts of deep convection and locally heavy rainfall Saturday and Sunday to mainly the eastern half of Big Island. The western portion of the state remains under a much drier and more stable airmass during the weekend for quieter weather. The surface trough begins to nudge east of the Big Island by Sunday afternoon as light northerly flow starts to build in from west to east. Medium range ECMWF and GFS guidance still shows another trough developing far northeast of the state by the middle of next week. This would put the state in a cooler northerly flow, but without much moisture or dynamical support for rainfall. A possible increase in showers may be felt Tuesday and Wednesday, if a weak cold front reaches the state, but this feature may not make it this far south intact. On the other hand, if subsequent guidance shifts the trough and front closer to the state, that would increase the threat for gusty north to northwest winds and rain showers and summit snowfall around the middle to end of next week. Will need to keep monitoring this period for shifts in guidance. && .AVIATION... Patches of mid-level clouds continue to stream across the eastern end of the island chain this afternoon. The background low level flow will remain light as a weak surface trough near the eastern Big Island tracks slowly westward. Sea breezes have allowed for cloud build ups over the island interiors this afternoon, and some showers to develop over Maui and the Big Island. AIRMET Sierra has been posted for tempo mountain obscurations on both islands. Clouds and showers may linger around Maui and the Big Island tonight, but the remaining islands should clear out with the land breezes. VFR conditions will prevail across the rest of the islands. && .MARINE... Minimal marine hazards are expected through the weekend. A surface trough near the Big Island and a weak high north of the area will keep light northeast winds over the smaller islands through Sunday. The winds will be light enough for sea breezes to develop during the day. Light to moderate southeast to south winds should be expected through the windward and southeast Big Island waters tonight and Saturday. Periods of heavier showers and a slight chance of thunderstorms are also expected over these waters through tonight. Light north winds will fill in Sunday around the Big Island. The surface trough will begin to shift east Sunday as high pressure builds to the northwest and a front passes to the north. A declining east swell will keep surf along east facing shores just below the advisory level tonight. This swell and surf will continue to trend down through the weekend. Surf elsewhere will remain quiet until the beginning of next week. A small northwest swell is forecast to peak Monday night, bringing surf below advisory levels. A hurricane force low is expected to develop off of Japan this weekend and send a large, long period northwest swell towards the islands midweek. The swell will begin building Tuesday and peak Wednesday night, with surf likely nearing warning levels. Additionally, a cold front will approach and may move into the area from the north Monday night through midweek, possibly bringing fresh to strong north winds and rough seas (small craft advisory conditions) across the waters Tuesday through midweek. && .HFO WATCHES/WARNINGS/ADVISORIES... None. && $$ DISCUSSION...Brenchley AVIATION...Foster MARINE...Eaton