Area Forecast Discussion
Issued by NWS Honolulu, HI
Issued by NWS Honolulu, HI
032 FXHW60 PHFO 041955 AFDHFO Area Forecast Discussion National Weather Service Honolulu HI 955 AM HST Tue Jun 4 2024 .SYNOPSIS... Breezy trades will continue today, before easing Wednesday and giving way to sea and land breezes Thursday and Friday. An upper level trough will bring the chance for an isolated thunderstorm over on the Kona slopes this afternoon. Otherwise, very dry conditions will overspread the entire island chain Thursday through the weekend, greatly limiting shower activity. Breezy trades returning early next week should bring the return of some windward showers. && .DISCUSSION... This morning`s satellite shows stable stratocumulus clouds moving into windward areas this morning and is producing a few light showers across the state. If we zoom out a little, altocumulus clouds are seen east and northeast of the Big Island. These clouds are associated with the isolated thunderstorms last night over windward Big Island. 12Z sounding from Lihue and Hilo show very steep mid level lapse rates due to a cold upper level trough over the state. This upper level trough should gradually move northeast and away from the state over the next 24 hours. For today, although the atmosphere in the upper levels remain unstable, at the surface we have a 1025 mb high centered northeast of the state producing our breezy trade winds. A drier air mass moving in today with a strong inversion at around 5500 feet should keep shower activity fairly light and mainly focused over windward areas. The one area of concern would be over the Kona slopes of the Big Island. Day time heating combined with some lingering upper level moisture will allow for showers and possibly a few isolated thunderstorms to develop over the slopes. Any showers or thunderstorms that do develop on the Big Island, should weaken during the evening and dissipate overnight. Trades are expected to weaken another notch on Wednesday as the ridge of high pressure north of the state drifts closer to the state. By Thursday, the ridge of high pressure will be very close to the state and we should the winds weaken another notch. Earlier runs of the ECMWF and GFS were in good agreement for light and variable winds on Thursday, but the latest ECMWF is now showing a light trade wind pattern. Although the trades will likely still be light enough for sea breezes to develop during the day time. From Friday into Saturday, winds will likely pick up a touch and we should see a light to moderate trade wind pattern. As far as precipitation, there will be little of it through the weekend. The Kona slopes should have a chance for showers each afternoon, but as a drier and very stable air mass moves in over the next few days, any shower activity will remain light. Elsewhere, with a strong mid level ridge overhead and drier than normal low level moisture, showers are not expected including windward areas. So overall, we should see plenty of sunshine with very few rain drops over the next several days. && .AVIATION... Breezy easterly trades will continue through today, then gradually weaken into tomorrow as the pressure gradient relaxes. Clouds and showers will favor windward and mauka locations with brief periods of MVFR conditions possible. Lingering elevated atmospheric instability over the state will allow for the potential development of isolated thunderstorms over interior and upslope sections of the Big Island this afternoon and evening. Stability will increase heading into Wednesday as mid level ridging strengthens over the state, cutting off the thunderstorm potential. AIRMET Sierra is in effect for mountain obscuration for windward Big Island and N thru SE sections of the smaller islands. This AIRMET will likely be needed through mid to late morning before conditions improve into the afternoon. AIRMET Tango for low level turbulence lee of island terrain remains in effect. This AIRMET will likely be needed through today, but will be cancelled by Wednesday morning as winds below the inversion decrease. && .MARINE... High pressure to the far northeast and northwest, with a ridge between the two, will maintain fresh to strong trade winds today, and as a result a Small Craft Advisory (SCA) remains in effect for all waters around the Big Island and Maui County, as well as selected areas around Oahu and Kauai. The ridge is expected to weaken through the day, and anticipate the SCA being trimmed back to the typical waters around Maui County and the Big Island through tonight. The ridge is expected to weaken and sink southward over the islands Thursday into Friday, which will lead to a significant decrease in the trades, which will likely lead to the SCA being dropped altogether. Over the weekend, the ridge is expected to lift northward, allowing moderate trades to return from south to north. The active south Pacific will continue to generate southerly swells here in the islands through the middle of the month. The current south-southwest swell got another pulse overnight but remains just below High Surf Advisory (HSA) criteria. This swell will gradually decline through Thursday, followed by a reinforcing south-southwest swell late Thursday and Friday that will produce south shore surf around seasonal average. A larger swell is expected to move through the islands this coming weekend, which will likely be near or at HSA levels of 10 feet. An potentially even larger swell is looking increasingly likely late next week that would bring surf well above advisory levels. A small northwest swell has continued to fill in overnight and looks to hold today. Another pulse from the northwest will follow Wednesday into Thursday. The fresh to strong trade wind flow is producing rough choppy elevated seas but the wind waves will diminish significantly after Wednesday coinciding with the light winds through the weekend. && .HFO WATCHES/WARNINGS/ADVISORIES... Small Craft Advisory until 6 PM HST this evening for Kauai Northwest Waters-Oahu Leeward Waters-Kaiwi Channel-Maui County Windward Waters-Maui County Leeward Waters. Small Craft Advisory until 6 AM HST Wednesday for Maalaea Bay- Pailolo Channel-Alenuihaha Channel-Big Island Windward Waters- Big Island Leeward Waters-Big Island Southeast Waters. && $$ DISCUSSION...Kino AVIATION...Farris MARINE...M Ballard