Area Forecast Discussion
Issued by NWS Honolulu, HI
Issued by NWS Honolulu, HI
153 FXHW60 PHFO 280148 AFDHFO Area Forecast Discussion National Weather Service Honolulu HI 348 PM 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. Meanwhile, a surface trough west of the islands and its attendant low aloft are producing an area of enhanced showers and thunderstorms that has now entered the offshore waters, approximately 150 nm west of Kauai. The afternoon sounding at Lihue has shown an increase of instability as the upper low associated with the trough to the west rotates northeastward and a weak shortwave advances towards Kauai. Elsewhere across the state, mostly stable conditions are observed this afternoon with scattered showers favoring windward and mauka locations. For the Big Island, daytime surface convergence has increased clouds and produced a few showers leeward as well. Rainfall totals have been mostly unremarkable today, however, as most showers have been light. Tonight through Tuesday, a trough aloft will quickly pass in close proximity to the western end of the state. This is expected to bring the aforementioned area of showers and thunderstorms to its closest point to the islands from tonight through Tuesday night. Based on the latest guidance, isolated thunderstorms have been introduced for the far northwest coastal waters just NW of Niihau with this afternoon`s forecast updates. However, guidance remains consistent in keeping this slightly too far northwest to impact Kauai. Elsewhere, shallow moisture embedded within the trades will produce some windward and mauka showers, especially during the overnight through early morning period. The low aloft west of the state will weaken as mid level ridging and the surface high to the far northeast strengthen from Wednesday onward. With the high remaining in place into the weekend, expect continued locally breezy trade winds, increasing stability, and a drier pattern during the second half of the week. && .AVIATION... Moderate to breezy trade winds will bring clouds and showers with periodic MVFR conditions to windward and mauka areas, with better coverage expected during the overnight to early morning hours. Otherwise and elsewhere, VFR conditions will prevail. With a weak shortwave trough passing just northwest of the state and increased mid level clouds around Kauai, the potential exists for light icing between 160 and FL250 and light to moderate turbulence between FL200 and FL340 through tonight. AIRMET Sierra is in effect for mountain obscuration for windward Big Island and N through SE sections of Maui through Oahu. This AIRMET may be needed for portions of the island chain through tomorrow morning. AIRMET Tango remains in effect for moderate low-level turbulence downwind of island terrain and may be cancelled later this evening if winds under the inversion fail to increase. Conditions for moderate low-level turbulence look marginal through the next couple of days and AIRMET Tango may be needed on and off through the period. && .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