Area Forecast Discussion
Issued by NWS Honolulu, HI
Issued by NWS Honolulu, HI
464 FXHW60 PHFO 081937 AFDHFO Area Forecast Discussion National Weather Service Honolulu HI 937 AM HST Wed May 8 2024 .SYNOPSIS... Expect moderate trades over the eastern islands through Thursday, while lighter trades and leeward land and sea breezes prevail over the western islands. Showers will favor windward slopes and coasts at night and interior and leeward areas each afternoon. Thunderstorms are possible Friday and Saturday as an upper disturbance moves through. Conditions should improve Sunday through early next week. && .DISCUSSION... High pressure far north of the main Hawaiian Islands drives moderate trades across local waters this morning. Satellite loop shows broken to overcast low clouds across windward areas while leeward areas appear to have scattered low clouds to clear skies. Overnight soundings depict seasonal amounts of PW, between 1.3 and 1.5 inches of PW, and a neutral to slightly unstable airmass. Subsidence inversions are noted between 5500 and 6500 feet, acting as deterrents to widespread and intense shower development. Radar shows scattered light to moderate showers beneath trade wind cloud cover. A front far northwest of the islands will shift southeastward over the next couple of days, eventually weakening into a broad trough across the islands on Friday. Trades will ease over the next few days in response. Expect moderate trade winds over the eastern islands today and Thursday, while lighter trades allow development of land and sea breezes across leeward areas of the western islands. Through Thursday, expect showers to favor windward and mauka areas overnight and during the morning, then transition over to interior and leeward areas each afternoon into the early evening. As the boundary layer flow becomes light and variable Thursday night, most showers should remain offshore. Models show trades will decrease further on Friday, allowing for sea breeze development statewide. Trades may strengthen over the weekend as the broad trough gradually weakens. By early next week, another front northwest of the state will cause surface flow to veer to southeasterlies across the western islands while trade flow persists across the eastern islands. Models show an upper low will move across the chain Friday through Saturday. Associated cold air aloft will destabilize our airmass and introduce the possibility of thunderstorms. At this time, predicted PW does not appear to be high enough to fuel a widespread heavy rain threat. However, brief heavy downpours associated with possible thunderstorms would cause minor flooding impacts. We will monitor model depictions over the next few days and issue appropriate watches if needed. Models also depict a potential for severe thunderstorms, with steep lapse rates, high CAPE, and strong bulk shear. If these conditions were to develop, stronger thunderstorms would be capable of producing hail and strong gusty winds. Expect a return of a hybrid trade wind pattern by Saturday night, featuring windward and mauka showers at night, followed by interior and leeward showers during the afternoon and early evening hours. && .AVIATION... Light to moderate trades are expected today with localized sea breezes developing later this morning for select leeward areas. Bands of light showers will continue to favor windward and mauka areas and be most active during the overnight hours. Over leeward areas, sea breezes will bring an increase of interior clouds and scattered showers this afternoon. Land breezes may also help to clear out cloud cover across leeward areas overnight. Brief MVFR conditions are to be expected in passing showers, otherwise VFR conditions will prevail statewide. No AIRMETs are in effect at this time. A subtropical jet passing just south of the state could bring light to moderate turbulence between FL300 to FL350 around the Big Island this afternoon through tonight. && .MARINE... Moderate trade winds will weaken over the next several days as high pressure northeast of the state moves further away and a cold front approaches the islands from the northwest. The front will weaken into a trough over the islands on Friday. Wind speeds should ease and become light to gentle Friday and Saturday with southeast flow over the eastern half and northeast to east flow over the western half of the state. Gentle to locally moderate east to southeast flow looks continue into the early half of next week across the coastal waters. Additionally, an upper level low will approach and move across the island chain. This will likely trigger heavy showers and possible thunderstorms, especially over the smaller islands Friday and Saturday. Surf along south facing shores will pick up as the weekend approaches. Forerunners from a larger and longer lived south- southwest swell are expected to arrive later this afternoon. Surf could reach High Surf Advisory (HSA) criteria Thursday or Friday before declining over the weekend. Meanwhile, the current northwest swell will continue to decrease to tiny conditions through tomorrow followed by a reinforcing short- period north northwest swell Friday and Saturday. Surf along east facing shores is expected to remain small as trade winds are expected to be light to locally moderate through the rest of the week. && .HFO WATCHES/WARNINGS/ADVISORIES... None. && $$ DISCUSSION...Powell AVIATION...Kino MARINE...Bedal/Wroe