769 FXHW60 PHFO 150702 AFDHFO Area Forecast Discussion National Weather Service Honolulu HI 902 PM HST Sun Oct 14 2018 .SYNOPSIS... A cloud band over Kauai will move southeast across Oahu and Maui County tonight through Monday, then stall and dissipate over the Big Island Tuesday. A high will build north of the area tonight and persist through the week. && .DISCUSSION... Satellite loops show a 90 mile wide band of showery low clouds running east northeast to west southwest over Kauai. This band is associated with the remnant of a front. Clouds associated with this band cover Kauai and Niihau and the coastal waters around Kauai County. Clouds are scattered over most areas from Oahu to the leeward side of the Big Island of Hawaii with patchy broken low clouds over windward Oahu. A trough extends northeast from over the Big Island. Broken to overcast low clouds associated with the trough cover the coast and lower slopes of the Big Island from Upolu Point to South Point and the coastal waters east of the Big Island. A surface ridge will build eastward north of the islands and moderate northeast trade winds will spread over the islands. The cloud band over Kauai will shift southeast slowly and weaken tomorrow, then stall and dissipate near the Big Island. Clouds and showers in the band will spread over Oahu and Maui tonight and tomorrow and reach the Big Island Monday night. The cloud band is rather shallow, so the showers in the band will affect mainly windward areas of the smaller islands, with only isolated showers spreading to leeward areas. A trough aloft is making the atmosphere less stable over the Big Island with deeper moisture there. Showers will be more active on the Big Island through tomorrow with some showers building over interior and leeward slopes tomorrow afternoon. As the trough aloft lifts north and weakens on Tuesday, the atmosphere over the Big Island will become more stable. From Wednesday through next weekend a surface ridge will persist north of the main Hawaiian Islands and maintain moderate to locally fresh northeast to east trade winds over the area. Ridging aloft will keep the atmosphere rather dry and stable, so showers will be focused over mainly windward areas with no heavy rainfall expected. Leeward areas will remain mostly dry. && .AVIATION... A diffuse frontal band continues to sag down across the central islands this evening. The northerly low-level flow behind this feature continues to produce overcast low clouds and frequent showers along north facing sections of Kauai. As a result, AIRMET Sierra remains in effect for mountain obscuration on that island. This AIRMET may persist through daybreak Monday morning. Elsewhere, broken to overcast low clouds and scattered showers associated with this band will likely produce brief periods of MVFR conditions over north and northeast facing slopes of most of the smaller islands from Oahu to Maui through early Monday morning. Otherwise, expect mainly VFR conditions to prevail over the smaller islands. Abundant moisture and a weak surface trough in the vicinity of the eastern end of the state continue to generate low clouds and showers over the southern and southeastern Big Island early this evening. AIRMET Sierra also remains in effect for mountain obscuration on that island from near Hilo to South Point. The low clouds and showers associated with the frontal band may begin to filter into the extreme northern end of the Big Island Monday morning. This may cause brief periods of MVFR to develop. AIRMET Tango for upper-level turbulence remains in effect over Hawaii between FL260 and FL420. This AIRMET will likely remain in effect through early Monday morning. Looking ahead to daytime Monday, the front will likely stall near Maui County before dawn Monday. The low-level flow is expected to become northeasterly during the day on Monday. Drier air moving into Kauai and Oahu may limit showers there after mid-morning Monday. However, low clouds and showers will likely continue to move into northeastern sections of the central Hawaiian islands, which may result in brief periods of MVFR conditions through late Monday afternoon. The surface trough near the Big Island is expected to weaken by Monday, so conditions will likely improve over the southeastern Big Island on Monday. && .MARINE... A weak front will stall across Maui County late tonight and gradually dissipate on Monday, while a trough near the Big Island falls apart. A surface ridge building north of the state will drive gentle to moderate north to northeast winds tonight, with moderate to locally fresh northeasterly trade winds settling over the island chain on Monday. Winds will peak just below Small Craft Advisory strength across Maui County waters Monday night and Tuesday, followed by a slight decrease on Wednesday and Thursday. An active surf pattern from the north and south is due this week. A pulse of shorter period north-northwest swell will push north shore surf to near October average tonight and early Monday. A larger north-northwest swell will arrive on Tuesday. Resulting surf will likely be well above the High Surf Advisory level for north facing shores on Tuesday and Wednesday, and combined seas over exposed waters may meet the 10 ft threshold for a Small Craft Advisory a that time. This swell will gradually lower Thursday and Friday and may be reinforced to around October average for next weekend. The run of late season south-southwest swells will continue through the week. Another pulse is expected to fill in tonight and hold through Monday, which will support moderate surf slightly above the October average. A gradual downward trend from this source is anticipated midweek. A larger south-southwest swell is expected to fill in on Friday and produce High Surf Advisory level surf through next weekend. Surf along east facing shores will remain below October average through the week, though a slight increase is due as winds pick up during the next couple of days. && .HFO WATCHES/WARNINGS/ADVISORIES... None. && $$ DISCUSSION...Donaldson AVIATION...Houston MARINE...Gibbs |