Area Forecast Discussion
Issued by NWS Honolulu, HI
Issued by NWS Honolulu, HI
615 FXHW60 PHFO 290151 AFDHFO Area Forecast Discussion National Weather Service Honolulu HI 351 PM HST Tue May 28 2024 .SYNOPSIS... High pressure to the north will maintain moderate to locally breezy trade winds through early next week. Showers will favor windward slopes and coasts, especially during the overnight and early morning hours. A trough aloft will move over the islands Friday through early next week, bringing an increase in trade wind shower coverage and intensity into early next week. && .DISCUSSION... This afternoon`s satellite imagery shows some scattered showers across the state mainly over windward mountains and along the kona slopes of the Big Island. A surface trough located west of Kauai continues to produce scattered thunderstorms just outside of our coastal waters. These thunderstorms and heavy showers are expected to remain west to northwest of Kauai, although you may visibly see them from the west side of Kauai. The trough west of the state is weakening the trades a touch around Kauai and Oahu with moderate east to east-southeast winds today. Meanwhile over on the eastern half of the state, we are seeing breezy easterly trades. For tonight and through Wednesday, we should see fairly similar weather conditions to today with scattered showers at times. Starting Thursday, the trough will drift further away from the area and we should see our breezy east-northeast trade winds across the state. Mostly dry conditions are expected during the day Thursday with a few isolated showers over windward areas. Although mostly dry conditions are expected, latest GFS simulated satellite imagery does show some high clouds drifting over the state on Thursday. The high clouds could make for a unique sunrise/sunset on Thursday. An upper level trough will begin to approach the state from the northeast on Friday, which should bring an increase of shower coverage across the state especially windward areas. With the breezy trade winds in place, windward areas could see frequent showers at times. From Friday through Saturday, we will remain on the backside of the upper level low, which is not a favorable area for instability. As we get into Sunday, the upper level low should be centered somewhere around Kauai, which is more favorable for greater instability. With the added instability, some brief downpours will be possible especially windward and mountain areas Sunday and possibly into the first half of next week. A slight chance of thunderstorms could be possible over the slopes of the Big Island Sunday afternoon, but confidence was not high enough to put it into the official forecast package. Stay tuned for updates. && .AVIATION... Moderate to breezy trade winds will bring clouds and showers with periodic MVFR conditions to windward and mauka areas. Otherwise VFR conditions will prevail. AIRMET Sierra is in effect for mountain obscuration across windward sections of Oahu and Kauai. This AIRMET may be needed along windward areas of the state periodically through tonight. Conditions for moderate low-level turbulence downwind of island terrain look marginal through the next couple of days and AIRMET Tango may be needed on and off through the period. Light icing will be possible around FL180 and FL250 across the western end of state today into tonight due high clouds streaming in and a low off to the northwest. && .MARINE... Fresh to strong easterly trades will continue through the week as the surface ridge remains positioned north of the state. A late morning ASCAT pass confirmed 25 kt winds are occurring over the windier waters and channels from Oahu to the Big Island, where a Small Craft Advisory remains in effect. Wind across the Kauai waters will fluctuate between east and east-southeast through Wednesday due to a persistent surface trough to the west. A shift out of the east-northeast is expected beginning around Thursday 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 next week due to an active pattern evolving within our swell window near New Zealand. Altimeter and ASCAT passes over the past couple of days showed 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 over 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. Guidance depicts a small, long-period swell arriving early next week from a gale that is forecast to track northeastward today over the far northwest Pacific near the Kuril Islands. && .HFO WATCHES/WARNINGS/ADVISORIES... Small Craft Advisory until 6 PM HST Wednesday for Kaiwi Channel- Maui County Windward Waters-Maalaea Bay-Pailolo Channel- Alenuihaha Channel-Big Island Windward Waters-Big Island Leeward Waters-Big Island Southeast Waters. && $$ DISCUSSION...Kino AVIATION...Farris MARINE...Vaughan