Area Forecast Discussion
Issued by NWS Honolulu, HI
Issued by NWS Honolulu, HI
679 FXHW60 PHFO 271423 AFDHFO Area Forecast Discussion National Weather Service Honolulu HI 423 AM HST Mon May 27 2024 .SYNOPSIS... High pressure north and northeast of the state will maintain moderate to locally breezy easterly trade winds through the week. Showers will mainly favor windward and mauka areas, with passing areas of high clouds at times. && .DISCUSSION... Broad high pressure far north of the islands continues to drive moderate to locally breezy trade winds across the state. Infrared satellite imagery shows an area of showers and thunderstorms roughly 600 miles west of Kauai associated with a nearly-stationary surface trough and its attendant low aloft. This feature is also causing local trades to veer slightly more east-southeasterly than usual, particularly across the western islands. Early morning soundings from Lihue and Hilo show mostly stable conditions with temperature inversions between 6000 and 7000 ft. The latest radar imagery shows scattered, mostly light, showers moving into windward areas as well as in some lee island plumes downwind of Oahu and Kauai. Rainfall totals have been scant, with only a few areas seeing up to a quarter of an inch in the last 6 hours. A small area of enhanced moisture is also moving into windward Big Island this morning, which will enhance showers there a bit into early afternoon. Little change is expected in the overall pattern through Tuesday, as high pressure gradually strengthens to the north/northwest 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 during the overnight through early morning hours each day. Additionally, expect spotty afternoon and evening showers, some briefly heavy, across leeward portions of the Big Island. The trough`s proximity to the western end of the state will weaken the inversion at times near Kauai and could enhance shower activity there, similar to last night. However, guidance is in agreement that the trough will remain far enough west of the main Hawaiian Islands to have little impact on local weather otherwise. For the rest of the week, the surface high will settle far northeast of the state and hold into Friday while the surface trough lingers west of the islands and produces breezy easterly trade winds. The nearby upper-level trough will weaken around mid- week, leading to greater stability and supporting a more typical trade shower pattern favoring windward and mauka areas. && .AVIATION... A fairly stable pattern will remain over the state for the next few days. Moisture embedded within the trade flow will allow for SHRA over windward and mauka areas. VFR conds should prevail over most locations, with MVFR conds possible in any SHRA. AIRMET Sierra is in effect for mtn obsc for windward Big Island and N through SE sections of the smaller islands. AIRMET Tango remains in effect for moderate low-level turb downwind of island terrain. This AIRMET will likely remain in effect through much of this week. With a weak shortwave trough passing just west of the state on Monday and increased mid level clouds around Kauai the potential exists for AIRMET Zulu to be needed for light icing between 160 and FL250 Monday afternoon through Monday night. && .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...TS AVIATION...SMW MARINE...Gibbs