Area Forecast Discussion
Issued by NWS Honolulu, HI
Issued by NWS Honolulu, HI
085 FXHW60 PHFO 250704 AFDHFO Area Forecast Discussion National Weather Service Honolulu HI 904 PM HST Tue Sep 24 2024 .SYNOPSIS... Gentle to breezy east trade winds will continue the next several days. Rainfall will be limited with more cloudiness and brief showers favoring windward exposures and higher terrain. The lone exception will be along Kona region slopes of Big Island where thicker cloud cover and showers will develop during daytime hours. && .DISCUSSION... A partly to mostly cloudy end to the day in paradise as cirrus debris clouds from thunderstorms far south of Hawaii (riding 10N latitude) race up within upper level southerlies primarily over the western half of the state while lower level stratocumulus move in from the east in the lower level trade belt. A large ridge of high pressure orientated parallel to the middle latitudes is this week`s main Central Pacific synoptic scale feature. The pressure gradient from the associated 1022 mb surface high centered between 30N and 40N latitude and along 150W longitude will continue to be the driver of gentle interior and breezy coastal and mauka east trades into October. Low pressure moving east across the Gulf of Alaska will ride atop this ridging and nudge it slightly closer to the island chain. Overall, this will have little to no effect on these ongoing gentle to breezy east trades the next several days. The only subtle effect would be a minor slackening of the gradient that could result in a hardly noticeable weakening of late week easterlies to more gentle magnitudes. The low will progressively move far northeast of the region this weekend, allowing the ridge to rebound to the north. This will likely correlate to the return of more statewide breezy east trades early next week. Mid to upper level ridging will build in over and north of the islands during the remainder of the week. This will translate to clearing out skies and result in a relatively drier weather pattern. Brief shower activity will favor windward areas and higher elevations, especially during the nocturnal hours. && .AVIATION... Moderate to locally breezy trade winds will continue due to high pressure to the north of the area. Upper level high pressure moving over the islands from the east will maintain a stable airmass during this time. Limited clouds and showers will be carried in on the trade winds, focusing what few showers make it to windward sides of the islands. Some afternoon clouds and showers are possible over the Kona slopes of the Big Island. VFR conditions are expected to prevail. No AIRMETs are currently in effect and none are anticipated at this time. && .MARINE... High pressure far north of the state will maintain moderate to locally strong trade winds through Wednesday afternoon. A Small Craft Advisory (SCA) remains in effect for the typical windy waters around Maui County and the Big Island during this time. Latest high resolution model data then shows conditions becoming borderline as the high fluctuates in strengthen through the rest of the week. Will continue to monitor latest observations overnight to see if conditions warrant an extension of the SCA. Global models have been trending towards a gentle to fresh tradewinds pattern developing over the weekend as a front passes far north of the state weakening the high far northeast of the area. Moderate to locally strong trades may rebound early next week as the front dissipates and a new high quickly rebuilds north of the state. For the offshore waters, a trough located far SW of the state will bring a slight chance of thunderstorms over the west and SW waters through tonight. A moderate long period northwest swell (320 to 330 degrees) filled in throughout the day today and should peak tonight then steadily decline the rest of the work week. Buoy 51001 and 51101 northwest of Kauai showed a peak swell height of around 6 to 7 feet 16 seconds earlier today. This should translate to surf peaking below advisory thresholds tonight for north facing shores of Kauai and Oahu. A smaller north-northwest swell should provide a boost this weekend. Surf along south facing shores will see a few pulses of small long-period southwest through the weekend from series of storms near the Tasman Sea last week. The first pulse appears to be peaking this evening based on latest reading from nearshore buoy readings. Another smaller long-period southwest swell is possible Friday slowly declining over the weekend with yet another small southwest pulse late Sunday. Additionally, a fetch of strong southwest winds near 10N170W yesterday should bring an increase of short-period energy from the southwest Wednesday into Thursday. East facing shores should remain small through much of the week and into the weekend due to the lack of strong trades locally or upstream of the state. && .HFO WATCHES/WARNINGS/ADVISORIES... Small Craft Advisory until 6 PM HST Wednesday for Maalaea Bay- Pailolo Channel-Alenuihaha Channel-Big Island Leeward Waters-Big Island Southeast Waters. && $$ DISCUSSION...Blood AVIATION...M Ballard MARINE...Almanza