Area Forecast Discussion
Issued by NWS Honolulu, HI
Issued by NWS Honolulu, HI
193 FXHW60 PHFO 040128 AFDHFO Area Forecast Discussion National Weather Service Honolulu HI 328 PM HST Thu Jul 3 2025 .SYNOPSIS... Stable trade winds will increase late Friday and will be breezy and gusty Saturday through at least Tuesday. Modest showers will be focused along windward slopes, and aside from afternoon showers over the Kona slopes of the Big Island, leeward areas will be mostly dry. && .DISCUSSION... Typical early summer conditions are in place. Broad surface high pressure north of the state is driving moderate to locally breezy trade winds, and mid level ridging is producing an inversion based between 6,500 and 7,500 feet. Precipitable water is running near to just below seasonal normal, and little organized moisture is observed in the trade wind flow. As a result, rainfall has been modest and focused over windward slopes, where less than a half of an inch has been measured during the past 24 hours, and most leeward areas have been dry. The only exceptions are the Kona slopes of the Big Island and portions of Upcountry Maui, where spotty afternoon showers will taper off later in the evening. Little change is expected into Independence Day. Trade winds will become breezy on Saturday, and the stable, gusty and rather dry conditions will persist through at least Tuesday. Trades will increase as surface high pressure far northeast of Hawaii strengthens to around 1032 mb. A mid level ridge will build overhead and push the inversion down to 5,000 to 6,500 feet. The interaction of the breezy trade wind flow with the islands should generate wind gusts around 40 mph over and downwind of terrain, though isolated areas on the Big Island and Maui County could approach Wind Advisory criteria at times. The GFS and ECMWF are showing no distinct organized areas of moisture with precipitable water below seasonal average. This should result in modest windward rainfall and aside from scattered afternoon and evening showers on the Kona slopes of the Big Island, dry leeward conditions. See the Fire Weather section below for additional discussion. A slight decrease in trade winds is expected Wednesday. && .AVIATION... Moderate to locally breezy trade winds will prevail across the island chain for the next several days. Low clouds and showers will focus mainly along windward and mountain areas, though some isolated showers could spill over into leeward areas from time to time. MVFR ceilings and visibilities will be possible within any passing showers, but VFR flight conditions will generally prevail at most locations throughout the next few days. AIRMET Tango has been issued today for moderate low-level turbulence over and downwind of island terrain. This AIRMET will likely persist into the weekend as breezy trades continue. && .MARINE... High pressure restrengthens and establishes north of the islands causing strong trades to develop this weekend. The existing Small Craft Advisory has been extended through the weekend and will require further expansion in areal coverage next week. Existing S swell declines through the weekend causing surf to fall below the summertime average. Tiny, long period S swell then holds into next week as below average surf continues. Wind waves and short period fresh swell will become more prominent as trades strengthen this weekend into next week. N shore remains tiny. && .FIRE WEATHER... Breezy, gusty, and rather dry conditions will develop on Saturday and persist into early next week. Relative humidity at lower leeward elevations will likely fall below 45 percent each afternoon, and with the inversion dropping to as low as 5,000 feet winds will become gusty over and downwind of terrain. This will result in near critical fire weather conditions over dry leeward areas, though no headlines (watches or warnings) are due since the Keetch Byram Drought Index will remain below the 600 threshold at Honolulu. && .HFO WATCHES/WARNINGS/ADVISORIES... Small Craft Advisory until 6 PM HST Sunday for Maalaea Bay- Pailolo Channel-Alenuihaha Channel-Big Island Leeward Waters-Big Island Southeast Waters. && $$ DISCUSSION...Wroe AVIATION...Vaughan MARINE...JVC FIRE WEATHER...Wroe