Area Forecast Discussion
Issued by NWS Honolulu, HI
Issued by NWS Honolulu, HI
121 FXHW60 PHFO 170149 AFDHFO Area Forecast Discussion National Weather Service Honolulu HI 349 PM HST Sat Aug 16 2025 .SYNOPSIS... Moderate to locally breezy trades will continue through tonight with passing windward and mauka showers. A low-level trough associated with the remnants of former Tropical Cyclone Ivo will move across the islands on Sunday and Monday bringing an increase in clouds and showers to mainly windward of mauka areas of the smaller islands. Another plume of moisture may bring an increase in clouds and showers on Wednesday. Otherwise, expect dry and stable conditions after Tuesday. && .DISCUSSION... Moderate to locally breezy trade winds continue this afternoon with mostly sunny skies and isolated showers moving across the state. Expect these conditions to continue through tonight as high pressure remains over the region and drier air briefly moves across the islands. Guidance continues to show a low-level trough associated with the remnants of former Tropical Cyclone Ivo moving across the islands on Sunday and Monday. Visible satellite imagery places the trough approximately 300 miles northeast of the Big Island this afternoon with CIMSS MIMIC PW around 1.5 inches. Expect relative humidity to steadily increase on Sunday as moisture associated with the trough filters into the islands. This trough will also bring a slight increase in instability to the region on Sunday and Monday which will allow the inversion to lift to around 8,000 to 9.000 feet. This will help to enhance clouds and showers across windward and mauka areas under a moderate to breezy trade wind pattern. Guidance has come into closer alignment today with the latest consensus showing the trough moving into Maui County by Sunday afternoon. Expect an uptick in showers across windward Maui by Sunday evening, with the moisture plume spreading westward into Oahu and Kauai County Sunday night into Monday. Rainfall totals through Monday will be around 0.5 to 1.0 inches across windward and mauka areas of the smaller islands. With the moisture plume staying north of the Big Island rainfall totals across windward and mauka areas will generally be less than 0.5 inches. The trough looks to exit the region towards the west on Tuesday, with high pressure quickly rebuilding across the area. However, guidance now shows another moisture plume moving into the area on Wednesday which may bring an increase in clouds and showers to windward and mauka areas. 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 through the rest of the weekend. Low cigs and SHRA possible mostly over windward and mauka areas with limited leeward spillover. MVFR conds expected in SHRA, otherwise VFR prevails. No AIRMETs in effect at this time. However, AIRMET Sierra may be needed overnight for mtn obsc as SHRA activity increases. && .MARINE... Ridging at all levels north of the area will expand into the northern waters and result in stable maritime conditions through most of next week. Widely scattered showers will pass across windward waters or form within plumes immediately downstream of the islands...except for early Monday where the remnants of Tropical Cyclone Ivo increase shower coverage. Surface high pressure centered far northwest of the islands will maintain a tight enough pressure gradient across the local waters to produce moderate to locally strong east trade winds. The Small Craft Advisory (SCA) will remain in effect from the Kaiwi Channel eastward and has been extended through Sunday afternoon. Trades are forecast to weaken just below SCA thresholds from Sunday night through early Monday morning as a weak trough from what is left of Tropical Cyclone Ivo pass through to the west and slacken the gradient. Moderate to locally strong trades will restrengthen from Monday afternoon and last through the remainder of the week. A two foot, medium period south southwest (180-200) swell is filling in today and will peak tonight. This swell should maintain waist to near head high surf along southern shores as it declines through a good part of the day Sunday. A series of very similar small, medium period south swells will pass around the islands through the upcoming week. These swells will assist in upholding seasonal standard surf along many south-facing shores. In response to this weekend`s moderate to fresh trade flow, east- facing chop will remain slightly elevated through Sunday. && .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 on Sunday and Monday bringing an increase in humidity and shower activity. Another plume of moisture may bring an increase in showers on Wednesday. Otherwise, lower humidity and more stable conditions are expected after Tuesday as high pressure rebuilds across the islands. && .HFO WATCHES/WARNINGS/ADVISORIES... Small Craft Advisory until 6 PM HST Sunday 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...Ahue AVIATION...Walsh MARINE...Blood FIRE WEATHER...Ahue