Area Forecast Discussion
Issued by NWS Honolulu, HI
Issued by NWS Honolulu, HI
254 FXHW60 PHFO 220644 AFDHFO Area Forecast Discussion National Weather Service Honolulu HI 844 PM HST Tue May 21 2024 .SYNOPSIS... Moderate to locally breezy trade winds will hold over the eastern islands, while lighter east-southeast winds allow for some localized land and sea breezes over the western end of the state through Wednesday. Showers will tend to favor windward and mauka areas overnight and during the morning hours, with a few showers developing over interior and leeward sections of Oahu and Kauai Wednesday afternoon and evening. Moderate to breezy easterly trade winds will spread over the state Wednesday night into Thursday and linger through early next week, with showers favoring typical windward and mauka areas. && .DISCUSSION... Currently at the surface, a trough of low pressure is located around 400 miles west-northwest of Kauai, while a 1035 mb high is centered around 1500 miles north-northeast of Honolulu. This light gradient will maintain moderate to locally breezy trade winds over the eastern islands, while light to moderate east-southeast winds remain over the western end of the state into Wednesday. This pattern will allow localized leeward sea breezes during the day and overnight land breezes for most sheltered areas over Kauai and Oahu. Satellite imagery this evening continues to show clouds over most windward areas, especially over windward Maui and the Big Island as an area of enhanced moisture more in. Expect rain chances to increase for windward areas statewide tonight into Wednesday as this area of enhanced moisture moves east. Moderate to breezy easterly trades will return statewide Thursday as the trough to the west-northwest of the state gradually shifts westward and the high to the northeast shifts north of the state. A series of reinforcing highs will build north of the state Friday through early next week, while the trough continues to shift further west and away from the area. This will maintain moderate to breezy trade winds across the island chain. In addition, drier air will filter in from the east allowing for a more stable trade wind pattern featuring mainly windward/mauka showers and the occasional leeward spillover. Showers will be mostly prevalent in the overnight and early morning hours. This pattern should hold through early next week. && .AVIATION... A trough to the west will continue to move away from the region, and a high pressure will remain to the northeast. This will maintain a moderate to breezy east to southeast flow over the islands through Wednesday. Moisture moving over the Big Island and Maui this evening is bringing clouds and showers to the east sides of those islands, bring MVFR and pockets of IFR conditions. This has also prompted AIRMET Sierra for mountain obscuration over those areas. Expect that to persist into Tuesday morning, and perhaps later. Windward clouds and showers may increase slightly across the rest of the island chain into tomorrow morning bringing some brief MVFR conditions. Otherwise, VFR conditions will prevail. && .MARINE... Strong high pressure far northeast of the state is driving fresh to strong easterly trade winds around the Big Island and Maui, and a surface trough northwest of Kauai is causing winds to shift out of the east-southeast over Oahu and Kauai. A Small Craft Advisory (SCA) remains in place for all waters around the Big Island, waters north of Maui, and the Pailolo Channel. As the trough weakens and drifts westward, expect the stronger easterly trades winds to spread to Oahu and Kauai on Wednesday, with the SCA likely adjusted to cover the typically windy waters around the Big Island and Maui County. Moderate to strong easterly trade winds will persist into the weekend. The south swell will continue to decline over south and exposed west shores through Wednesday. Only small long period background south swell pulses are expected from Tasman Sea sources into the first half of next week. Rough surf along east facing shores will slowly rise over the next few days as the trades strengthen upstream of the state. Surf heights along north and west facing shores will remain small with a slight bump up from Sunday into Monday. && .HFO WATCHES/WARNINGS/ADVISORIES... Small Craft Advisory until 6 AM HST Thursday for Maui County Windward Waters-Pailolo Channel-Alenuihaha Channel-Big Island Windward Waters-Big Island Leeward Waters-Big Island Southeast Waters. && $$ DISCUSSION...Ahue/Almanza AVIATION...M Ballard MARINE...Bohlin