Area Forecast Discussion
Issued by NWS Honolulu, HI
Issued by NWS Honolulu, HI
560 FXHW60 PHFO 210639 AFDHFO Area Forecast Discussion National Weather Service Honolulu HI 839 PM HST Fri Sep 20 2024 .SYNOPSIS... Breezy easterly trades will continue through Saturday, then briefly ease into the light to moderate range Sunday through Monday as the surface ridge weakens to the north. Showers will primarily favor windward and mauka locations, though a few could reach leeward and interior areas as an upper disturbance drifts southward over the region Sunday. Breezy trades and more stable conditions are expected to return Tuesday, persisting into the latter half of next week. && .DISCUSSION... Guidance remains in good agreement, showing breezy easterly trades holding through Saturday as the surface ridge stays far north of the state. Evening satellite imagery shows a couple of sizable areas of low clouds approaching from the east, which may lead to enhanced windward and mauka shower coverage overnight into Saturday as they move through. A slight transition is expected Saturday night through Monday as upper heights lower in response to a broad, weak upper low drifting southward into the area, while the surface ridge weakens. Lighter trades, combined with a weakened subsidence inversion, could lead to increased windward showers, with some either spilling over into leeward and interior areas or forming over leeward areas due to localized sea breezes in the afternoon. The best chance for thunderstorms will remain north of the state where the better mid-level lapse rates and deeper moisture are expected. Upper heights will rise Monday night through midweek as the upper low fills and lifts away. This, combined with the surface ridge rebuilding to the north, will support a return to a more stable and breezy trade wind pattern. Although confidence is low this far out, some models suggest an area deeper tropical moisture associated with a disturbance passing far south of the state clipping portions of the area late next week. Expect a wetter trade wind pattern for these areas if this were to materialize. && .AVIATION... Moderate to locally breezy trades are expected through the rest of tonight. An upper level low is anticipated to move over the state during the weekend time frame. Enhanced SHRA are expected mostly over windward and mauka locations, with limited spillover to leeward areas. MVFR conds can be expected with isolated IFR conds in heavier prolonged SHRA. VFR should generally prevail outside of SHRA activity. No AIRMETs are in effect. With an increase in SHRA overnight AIRMET Sierra may be needed for mtn obsc for windward locations during the overnight hours through this weekend. && .MARINE... A high pressure ridge far north of Hawaii will keep fresh to strong easterly trade winds in the forecast through Saturday. A cold frontal system passing through the far northern Central Pacific basin will weaken the ridge from Sunday through Monday, briefly easing trade wind speeds into the gentle to moderate range. A Small Craft Advisory (SCA) remains in effect for the windier waters around Maui County and the Big Island through Saturday. Fresh trade winds should return by Tuesday of next week and the trades may approach SCA thresholds for our typical windier waters around Maui County and the Big Island once again. Surf along north and west facing shores will trend up beginning next Tuesday in response to a gale developing near the Kurils, racing eastward across the Date Line near the Aleutians this weekend, then to the Gulf of Alaska early next week. Guidance shows this northwest swell peaking locally Tuesday night into Wednesday out of the northwest, then fading Thursday into Friday as it shifts out of a more north-northwest direction. Surf along south facing shores will remain small through the weekend, with mainly a mix of background long-period southwest and short-period southeast swells moving through. An upward trend is possible Tuesday through midweek due to a slightly larger southwest swell arriving. Surf along east facing shores will remain small and choppy into Saturday, then decrease Sunday into next week as the trades lower locally and upstream across the eastern Pacific. && .HFO WATCHES/WARNINGS/ADVISORIES... Small Craft Advisory until 6 PM HST Saturday for Maalaea Bay- Pailolo Channel-Alenuihaha Channel-Big Island Leeward Waters-Big Island Southeast Waters. && $$ DISCUSSION...Gibbs AVIATION...Walsh MARINE...Bohlin