Area Forecast Discussion
Issued by NWS Honolulu, HI
Issued by NWS Honolulu, HI
968 FXHW60 PHFO 271948 AFDHFO Area Forecast Discussion National Weather Service Honolulu HI 948 AM HST Mon May 27 2024 .SYNOPSIS... High pressure northeast of the state will maintain moderate to locally breezy easterly trade winds through the week. Showers will mainly favor windward and mauka areas, especially during the overnight through early morning hours each day. A drier trade wind pattern is expected during the second half of the week. && .DISCUSSION... Moderate to locally breezy trade winds continue across the islands today with broad high pressure north of the state. Latest regional satellite imagery shows an area of showers and thunderstorms associated with a nearly stationary surface trough and its attendant low aloft. These thunderstorms are now located about 250 nm west of Kauai, just outside of the offshore waters. Early morning soundings from Lihue and Hilo showed mostly stable conditions with temperature inversions between 6000 and 7000 ft. Showers that were more common earlier this morning across windward Oahu have noticeably decreased since about 7am HST, though a narrow band of low-level moisture embedded within the trades continues to produce scattered light showers and clouds across eastern sections of Maui and Molokai. In the near term, shower chances and coverage have been lowered through the rest of the morning for much of the Big Island, which is located south of the primary band of low-level moisture affecting Maui County. However, the overall forecast philosophy remains in tact. Little change is expected in the overall pattern for the rest of Memorial Day, as high pressure gradually strengthens to the north/northeast and the surface trough and upper low west of the state remain nearly stationary. Shallow moisture embedded within the trades will produce some windward and mauka showers at times, particularly tonight through early Tuesday. Additionally, expect spotty afternoon and evening showers across leeward portions of the Big Island. The low aloft west of the islands will swing around to the northeast tonight through Wednesday. This will bring the area of enhanced showers/thunderstorms closest to the main Hawaiian Islands- within in the offshore waters, and possibly grazing the far NW coastal waters, during this time. However, guidance remains in agreement that the trough will remain far enough west of the state to have little impact on island weather as ridging aloft builds from the south and the surface high to the far northeast strengthens. For the rest of the week, the surface high far northeast of the state will gradually strengthen and hold into the weekend. Expect increasing stability and a drier trade wind pattern during the second half of the week. && .AVIATION... Moisture riding in on the moderate to breezy trade winds will bring clouds and showers to windward and mauka areas, with better coverage expected during the overnight to early morning hours. MVFR conditions will be possible with this activity. Otherwise and elsewhere, VFR conditions will prevail. This pattern will hold over the next couple of days. AIRMET Sierra is in effect for mountain obscuration for windward Big Island and N through SE sections of the smaller islands. This AIRMET may be cancelled later this morning or afternoon as conditions improve. AIRMET Tango remains in effect for moderate low-level turbulence downwind of island terrain. With a weak shortwave trough passing just west of the state today and increased mid level clouds around Kauai, the potential exists for light icing between 160 and FL250 for this afternoon through tonight. && .MARINE... Moderate to strong easterly trades will continue through the week as the surface ridge remains positioned north of the state. The strongest winds are expected over the windier waters around Maui County and the Big Island, supporting the Small Craft Advisory. The lightest winds are anticipated over the Kauai waters, fluctuating between east and east-southeast over the next few days due to a persistent surface trough to the west. A shift out of the east-northeast is likely later in the week as the trough weakens and drifts away from the region. Surf along exposed south-facing shores will remain small throughout much of the week, due to a combination of background south-southwest and southeast swell energy. An upward trend is expected from Friday through the first week of June due to an active pattern setting up within our swell window near New Zealand. Altimeter and ASCAT passes over the past couple of days reflected the potential for next weekend, showing a broad swath of gale-to storm-force winds with seas up to 30 feet focused at the state within the 190-200 degree directional bands. This will mark the beginning of a long-lived event with additional reinforcements expected within the same area over the next several days. Surf along exposed east-facing shores will remain small and choppy throughout the week as the trades persist. Surf along north-facing shores will remain near the summertime average each day, with only small background northwest pulses expected today and potentially next weekend. && .HFO WATCHES/WARNINGS/ADVISORIES... Small Craft Advisory until 6 PM HST Tuesday for Pailolo Channel- Alenuihaha Channel-Big Island Leeward Waters-Big Island Southeast Waters. && $$ DISCUSSION...Vaughan AVIATION...Farris MARINE...JVC