Area Forecast Discussion
Issued by NWS Honolulu, HI
Issued by NWS Honolulu, HI
986 FXHW60 PHFO 171335 AFDHFO Area Forecast Discussion National Weather Service Honolulu HI 335 AM HST Sun Aug 17 2025 .SYNOPSIS... Moderate to locally breezy trades persist through the morning with passing windward and mauka showers. Later today, a low-level trough associated with the remnants of former Tropical Cyclone Ivo will propagate across the islands, bringing increased clouds and shower activity predominately to the windward and mauka areas. By midweek, another plume of moisture is expected to passing into the region, again increasing clouds and showers. Otherwise, drier and more stable conditions prevail through the remainder of the week. && .DISCUSSION... Broad area of high pressure remains quasi-stationary north of the islands, allowing moderate to locally breezy trades to prevail with passing windward and mauka showers. Latest deterministic model guidance of the GFS and ECMWF are in strong agreement supporting a quick moving, low-level trough associated with the remnants of former Tropical Cyclone Ivo to propagate toward Maui County later this afternoon before shimmying northwestward. As the trough approaches, relative humidity levels will increase slightly today into Monday as moisture associated with the trough begins to filter onto the islands. Trades will weaken briefly, maintaining light to moderate trades across the region. The trough will also bring a slight increase in instability to the region, allowing the inversion to lift around 8,000 to 9,000 feet. Expect an uptick in shower activity across windward Maui by Sunday evening, with the moisture plume spreading westward into Oahu and Kauai County Sunday night into Monday. Rainfall totals up to 0.25 inches across windward and mauka areas of the smaller islands with locally higher amounts possible within this fast moving system. By Tuesday, the aforementioned trough exits the region, with high pressure quickly rebuilding in its wake, allowing moderate to locally breezy trades return. However, latest guidance now showcases another moisture plume propagating into the vicinity Wednesday, which may enhance cloud coverage and shower activity to windward and mauka areas again midweek. Otherwise, expect predominately dry and stable conditions to return for the latter half of the forecast period, with typical summertime conditions yielding limited clouds and showers across the state under moderate to breezy trades. && .AVIATION... Moderate to locally breezy trades persist through the forecast period. Brief periods of MVFR conditions possible in low ceilings and showers, predominately windward and mauka areas with limited leeward spillover. Otherwise, VFR conditions prevail No AIRMETs in effect at this time, however, as a low-level trough moves into the region, AIRMET Sierra may become necessary for mountain obscuration due to incoming shower activity. && .MARINE... Persistent ridging north of the state will lead to a rather stable weather pattern with typical fresh to locally strong trades through a majority of the of the forecast period. The Small Craft Advisory (SCA) will remain in effect from the Kaiwi Channel eastward through this afternoon. Trades are forecast to weaken just below SCA thresholds tonight through early Monday morning as a weak trough from the remnants of Tropical Cyclone Ivo pass from east to west over the smaller islands. Moderate to locally strong trades will restrengthen Monday afternoon and maintain strength through the remainder of the week. A 2 to 3 foot, medium period south southwest (180-200) swell will hold today and generate waist to chest high surf, near seasonal norms. A series of very similar small, medium period south swells will pass through the local waters through the work week. These swells will help to maintain seasonal surf heights along the south- facing shores, well below advisory thresholds. Expect chop along east facing shores to remain elevated today, then lower tonight into Monday morning as trades weaken slightly. Fresh trades will once again bring elevated choppy conditions to east facing shores Monday afternoon through mid- week. Flat to tiny surf will persist along north facing shores through the forecast period. && .FIRE WEATHER... Conditions should remain below critical fire weather thresholds into early next week. A low-level trough associated with the remnants of former Tropical Cyclone Ivo will move across the state later today through Monday, bringing an increase in humidity and shower activity. By midweek, another plume of moisture is expected in the vicinity of the islands, which may increase shower activity again on Wednesday. Otherwise, expect dry and stable conditions for the latter half of the week as high pressure rebuilds across the islands. && .HFO WATCHES/WARNINGS/ADVISORIES... Small Craft Advisory until 6 PM HST this evening for Kaiwi Channel-Maui County Windward Waters-Maui County Leeward Waters- Maalaea Bay-Pailolo Channel-Alenuihaha Channel-Big Island Windward Waters-Big Island Leeward Waters-Big Island Southeast Waters. && $$ DISCUSSION...Pierce AVIATION...Pierce MARINE...Thomas FIRE WEATHER...Pierce