Area Forecast Discussion
Issued by NWS Honolulu, HI
Issued by NWS Honolulu, HI
367 FXHW60 PHFO 061957 AFDHFO Area Forecast Discussion National Weather Service Honolulu HI 957 AM HST Mon Jan 6 2025 .SYNOPSIS... Gentle to locally breezy southwest winds will gradually strengthen today across the western end of the state as a front slowly approaches from the northwest. Clouds and showers will be focused along kona coasts and slopes. The front is expected to shift down to island chain Tuesday night before stalling and dissipating around the Oahu and Maui County Wednesday shifting clouds and showers along northern exposures. Moderate trades are expected to return during the second half of the week with clouds and showers mainly focused along windward and mauka areas. Showers will remain enhanced as upper level instability increases over the state. && .DISCUSSION... Latest satellite and radar imagery show clouds and showers over kona coasts and slopes as gentle south and southwesterly winds prevail over the state. Total rainfall accumulations remain light as weak mid- level riding keeps an inversion layer between 5.5- 6 kft based on the morning sounding. As the day progresses expect clouds and chances of showers to increase over interior and kona slopes. This will be partly due to diurnal pattern and the middle level ridge eroding, allowing for clouds to develop more and increasing low level moisture. Over the eastern half of the state gentle south to southwest winds will shift the vog plume mainly over the Big Island for the next couple of days. Latest model guidance continues to show an upper level trough deepening west of the state today and tonight that will reinvigorate a nearly stationary frontal boundary northwest of Kauai. Expect southwest winds over the western half of the state to gradually strengthen becoming breezy late tonight into Tuesday as the front moves south. Hi resolution model guidance keeps light to moderate showers focused along kona coasts and slopes. The front is expected to move over Kauai Tuesday night before weakening an shifting over Oahu Wednesday. Increased upper level instability from the trough and low level moisture riding in ahead of the front will increase chances of precipitation and intensity from light to moderate to locally heavy mainly for exposed northern exposures. Wednesday night into Thursday, amplified upper level ridging to the east of the state will deepen the upper level trough over state Thursday into the weekend. Lingering low- level moisture from the dissipating front will become enhanced as another area of moisture is advected in from the southeast. This along with the returning trades as a surface high builds north of the state behind the front and tracks northeast will keep enhanced precipitation in the forecast but shift the focus along windward and mauka areas. The anomalous cold upper level temperatures could also increase chances for thunderstorms around the upper slopes of the Big Island Friday and Saturday but have left them out of the forecast at this time since the probabilities. However, model guidance is trending up with each model run so bears watching and mentioning. && .AVIATION... A cold front is approaching the islands from the northwest and will remain northwest of the state today. Ahead of this feature, light to moderate southerly to southwesterly winds will prevail through Tuesday. Winds may be light enough for localized land and sea breezes to develop in terrain sheltered areas. Meanwhile, a pre-frontal convergence band of moisture will continue to produce clouds and a few showers streaming from the south across Maui County and Kauai today. The band over Maui County is forecast to lift northward over Oahu tonight. The front is expected to make its way across Kauai by late Tuesday, increasing showers and low clouds as it moves through. This morning, AIRMET Sierra remains in effect for IFR conditions at Lanai, where ceilings have been broken to overcast at around 300 feet since midnight. Based on latest satellite trends, the IFR should lift at Lanai by late morning. Additionally, AIRMET Sierra also remains in effect for mountain obscuration for SW through W sections of Kauai, Molokai, and Maui. && .MARINE... Overlapping significant swell energy will maintain warning level surf heights along exposed north and west facing shores. The High Surf Warning (HSW) is now in effect through Wednesday morning for north and west facing shores of Niihau, Kauai, Oahu, and Molokai, north facing shores of Maui, and west facing shores of the Big Island. A Small Craft Advisory (SCA) is also in effect through Wednesday morning for all Hawaiian coastal waters except Maalea Bay. Seas 10 ft or greater are expected for all waters exposed to west and northwest swells. Both the HSW and SCA will likely need to be extended through at least Thursday. According to latest model guidance, the current west-northwest (290-310 degree) swell will hold surf heights just above HSW criteria through Tuesday. Surf heights will then rapidly climb with the arrival of an extra-large reinforcing swell out of the northwest (310-330). The swell is expected to peak by Wednesday morning then slowly decline. Surf heights along north and west facing shores should drop back below warning levels no later than Thursday evening. Surf heights along east and south facing shores will remain small through the forecast period. Over the western islands, moderate to fresh southwesterlies will continue to blow into Tuesday, and then become more northerly winds from Tuesday night into Wednesday as a weak cold front moves across the islands. Wind directions will then shift back to moderate to fresh northeasterly to easterly trade winds by Thursday. Across the eastern end of the state, gentle to locally fresh southeast winds will hold today, then become light and variable by Tuesday before transitioning back to moderate trades on Thursday. && .FIRE WEATHER... No critical fire weather conditions are expected through the forecast period. Gentle to locally breezy southerly flow will help increase moisture around the state, especially for leeward areas. A front is expected to move through the western part of the state late Tuesday through Wednesday, increasing potential for rainfall. Moderate trades wind will fill in behind the front. Increasing upper level instability and lingering moisture over the state will keep an enhanced potential for rainfall over the state but mainly focused over windward and mauka areas. && .HFO WATCHES/WARNINGS/ADVISORIES... High Surf Warning until 6 AM HST Wednesday for Niihau-Kauai Leeward-Waianae Coast-Oahu North Shore-Maui Windward West-Kona- Kohala-Kauai North-Molokai Windward-Molokai North-Molokai West- Maui Central Valley North-Windward Haleakala-Big Island South. Small Craft Advisory until 6 AM HST Wednesday for all Hawaiian waters except Maalaea Bay- && $$ DISCUSSION...Almanza AVIATION...Vaughan MARINE...Bedal FIRE WEATHER...Almanza