Area Forecast Discussion
Issued by NWS Honolulu, HI
Issued by NWS Honolulu, HI
479 FXHW60 PHFO 160144 AFDHFO Area Forecast Discussion National Weather Service Honolulu HI 344 PM HST Tue Sep 15 2026 .SYNOPSIS... Moderate trades will strengthen to breezy levels Wednesday and hold through the forecast period. Moisture will continue to fill in across the state from east to west tonight into Friday increasing chances of showers mainly for windward and mauka areas. Chances of heavy rain, isolated thunderstorms and flood potential will increase Thursday into Friday as an upper level disturbance moves overhead. Drier air will move back in this weekend as trades continue. Moisture from the remnants of Tropical Depression 15-E may bring another round of enhanced trade showers early next week. && .DISCUSSION... Radar and satellite show light to moderate showers over mauka areas of Oahu and portions of Maui County. A cluster of moderate showers remains upstream of Kauai. The highest rainfall totals through the day were observed at West Wailuaiki with 1 inch of rainfall in the past 3 hours. Oahu windward areas received between .20 to .40 inches in the past 3 hours. Elsewhere mainly light showers were focused along windward and mauka areas. Gentle to moderate trades were observed across the state. A large area of enhanced moisture as seen in the CIMSS precipitable water imagery is still making its way across the state from east to west. Thus expect and increase in scattered light to moderate showers tonight that will focus primarily along windward and mauka areas. Although upper level ridging should limit the potential of heavy showers, brief heavy showers cannot be ruled out overnight especially for Kauai as the cluster of enhanced showers moves over the complex terrain. An upper level trough will sink down over the state Wednesday afternoon and evening just as the deepest surge of moisture from Norbert begins to move across the state. This will result in a sharp increase in moderate to heavy showers from late Wednesday night through early Friday. Instability will be sufficient for an isolated thunderstorm as well. A flood watch may be needed for Thursday but could be issued as early as Wednesday. Moisture will decrease late Friday through the weekend. Latest guidance remains on track, showing another area of increasing moisture (from the remnants of tropical depression 15-E) will likely move into the area Monday or Tuesday next week. The GFS shows better upper level support that could enhance the trade showers while ECMWF shows mid level ridging that could help limit heavy shower potential. Will continue to monitor all available guidance to determine exact impacts with future updates. && .AVIATION... The forecast is on track as the trade winds continue to gradually strengthen and become locally breezy this afternoon into the evening. Isolated to scattered showers have slowly been passing by the islands, while we`ve seen an increase in cloud and shower activity on the windward sides of the island. MVFR conditions will be possible in passing showers. Otherwise, VFR conditions will prevail. A similar set up is expected for Wednesday, with wetter weather returning on Thursday. AIRMET Sierra is in effect for tempo mountain obscuration for windward areas of the Big Island through Oahu, including Lanai. Conditions are expected to improve or end around 0400Z. && .MARINE... Prominent low pressure south of the islands maintains fresh trades from tomorrow onward. A Small Craft Advisory will be needed for Wednesday and potentially beyond. Remnants of TC Norbert will bring isolated thunderstorms to area waters Thursday night through Friday night. Long period energy out of the S to SW fills in during the latter half of the week supporting building surf for S shores. Surf is initially small through Wednesday but will trend upward toward the High Surf Advisory threshold by this weekend. Surf along E shores will modestly increase in response to building trades and a brief medium period E swell emanating from former TC Norbert. N shores stay flat to tiny. && .FIRE WEATHER... Fire weather risk should remain low through the remainder of the week due to moderate winds and increased relative humidity and moisture from the remnants of Norbert. Showers will dramatically increase late Wednesday into early Friday. Inversion heights from Maui to the Big Island will be elevated around 7,500 to 8,500 ft. && .HFO WATCHES/WARNINGS/ADVISORIES... None. && $$ DISCUSSION/FIRE WEATHER...Almanza AVIATION...KR MARINE...JVC