Area Forecast Discussion
Issued by NWS Honolulu, HI
Issued by NWS Honolulu, HI
407 FXHW60 PHFO 181339 AFDHFO Area Forecast Discussion National Weather Service Honolulu HI 339 AM HST Sat Oct 18 2025 .SYNOPSIS... A upper-level low currently northeast of the Hawaiian Islands will move south over the next several days, aiding in maintaining relatively unstable conditions. Moderate to locally breezy trades will also continue through today into tonight. This combination will continue to bring enhanced showers and a slight chance of thunderstorms to the region throughout the next couple days. && .DISCUSSION... Latest satellite imagery continues to illustrate thunderstorm activity north and west of Kauai and Niihau this morning progged to move further westward away, while extensive cloud cover blankets Maui and the Big Island. Observations over the past few hours have indicated that light precipitation has fallen over the Hawaiian Islands, with the heaviest fallen over much of Maui and western portions of Molokai. Trends suggest that additional precipitation is expected, primarily across windward and mauka areas for all islands through early tomorrow morning before clearing Sunday. Moderate to locally breezy trades continue today into tonight, maintaining enhanced shower activity across windward and mauka areas. Winds thereafter begin to ease to a light to locally moderate pattern persisting through midweek. Trades strengthen toward the latter end of the week and prevailing through the weekend. Model guidance of the GFS and ECMWF also continues to depict an upper-level trough will remain over the vicinity of the Hawaiian Islands, sustaining unstable conditions. Within said trough remains two individual closed low circulations that have been steering the state`s weather these last couple days. One is situated to the west of the island chain and is propagating westward away, while the second is positioned northeast of the islands. The previous discussion mentioned that the second closed low will end up centered very close to the islands by Wednesday, however, latest guidance has depicted the circulation to stay east of the islands at this time while propagating southward through the remainder of the outlook period. Much of the coldest air aloft has been progged to remain north of the island chain, limiting any thunderstorm potential, however, model guidance does hint at periods of enhanced shower activity throughout the week in conjunction with the wet trades regime. && .AVIATION... An upper level low pressure system west of the state continues to create an unstable atmosphere allowing enhanced showers to be embedded within easterly trade winds. These showers are mostly focused over windward and mountain areas, but they can spread into leeward areas as well. MVFR conditions are expected within passing showers, otherwise VFR conditions prevail. AIRMET SIERRA is not in effect, but could be issued tonight due to potential low clouds and showers causing mountain obscurations. AIRMET Tango is in effect across the island chain for tempo moderate turbulence between FL300 and FL350. Conditions will continue through the evening but will likely weaken later tonight. High clouds streaming over Maui and the Big Island are causing light icing conditions in LYR 155-FL210. These conditions are expected to continue through the evening, but chances of light icing should decrease late tonight. && .MARINE... Moderate to locally strong trades will remain in place over the Hawaiian coastal waters through today. Trades then weaken into the moderate to locally fresh range through early next week. A Small Craft Advisory (SCA) remains in effect over the windier waters and channels surrounding Maui County and the Big Island through Saturday afternoon. An upper low north of Kauai will continue to drift over the northern waters through the weekend keeping a slight chance of thunderstorms in the forecast. Two moderate, long-period NW and NNW swells moving through the waters will maintain elevated surf along N and W facing shores through Saturday and then trend down on Sunday. A hurricane force low E of Japan will bring another round of moderate, long- period NW (330 deg) swell into the islands towards the middle of next week leading to building surf along N and W facing shores. This next long-period swell may reach low-end High Surf Advisory thresholds Wednesday into Thursday. A series of small, medium-to long-period S to SW swells will filter into the area through the weekend keeping surf along S facing shores from going flat. Short-period surf along E facing shores increases slightly on Saturday due to the stronger trades, then trends down slightly Sunday through early next week. && .FIRE WEATHER... Wind speeds and afternoon minimum humidity levels will remain below critical fire weather thresholds through the forecast period. Locally heavy rain and thunderstorms are possible through this morning. Unstable conditions will continue to produce wet weather across the state through early next week. Temperature inversion heights near Maui and the Big Island will range from the 8,500 to 9,500 feet today. && .HFO WATCHES/WARNINGS/ADVISORIES... Small Craft Advisory until 6 PM HST this evening for Maalaea Bay- Pailolo Channel-Alenuihaha Channel-Big Island Leeward Waters-Big Island Southeast Waters. && $$ DISCUSSION...Pierce AVIATION...Bohlin MARINE...JVC FIRE WEATHER...Pierce