Area Forecast Discussion
Issued by NWS Honolulu, HI
Issued by NWS Honolulu, HI
022 FXHW60 PHFO 121339 AFDHFO Area Forecast Discussion National Weather Service Honolulu HI 339 AM HST Sat Jul 12 2025 .SYNOPSIS... High pressure well northeast of the islands will maintain moderate to locally breezy trades, weakening slightly as the high begins to drift further away from the islands. Expect passing clouds and showers to favor windward and mauka areas, with a slight uptick in shower activity through the weekend and into early next week. && .DISCUSSION... High pressure persist northeast of the islands, maintaining moderate to locally breezy trades through the next several days. Model guidance of the GFS and ECMWF continues to support the high drifting further northeastward throughout the weekend and into early next week, allowing trades to weaken slightly, though wind- prone locations will tend to remain on the breezier side. On the contrary, an increase in sea breeze activity will be possible for sheltered western slopes of island mountains. Latest observations from low-level water vapor imagery continues to display a compact low just north of the islands slowly meandering westward. Despite its quasi-stationary status, an associated shortwave trough will migrate into the vicinity of the islands, assisting in raising inversion heights a bit throughout the weekend. The 12z inversion heights at Lihue and Hilo are 7000 to 8000 feet, respectively. This, in conjunction with an area of moisture east of the offshore waters, may result in enhanced shower activity, especially across windward and mauka areas, but can still linger into leeward areas as well. By early next week, model guidance is depicting another area of moisture moving east to west tracking toward the islands. While the ECMWF hints at this moisture missing north of the islands, the GFS is much more aggressive, suggesting a slight uptick in windward and mauka shower activity through the early portion of next week. Thereafter by Tuesday evening, a resumption of typical summertime trades is in order as guidance hints at the aforementioned high pressure building back up, increasing the local pressure gradient. As a result, trades may increase slightly for the latter half of next week, but confidence is too low at this time to say anything with absolute certainty this far out in time. && .AVIATION... Moderate to locally breezy trades will persist through the weekend. Clouds and showers will favor windward and mountain areas across all islands and may result in MVFR conditions at times. Otherwise, VFR conditions will generally prevail. No AIRMETs are in effect at this time, however, AIRMET Sierra for mountain obscuration may be needed later in the forecast period. && .MARINE... The high pressure ridge will weaken north of the Hawaiian Islands, decreasing trade winds speeds through Monday. The ridge will strengthen from Tuesday onward increasing trade wind speeds back into the moderate to locally strong range through the end of next week. Wind speeds have fallen below Small Craft Advisory (SCA) levels this morning and thus the advisory was cancelled. SCA conditions may return by Tuesday as wind speeds increase once again. Surf along south facing shores will remain small through the weekend as a small background south southwest swell moves through. A small, long period south swell will build in from Sunday night into Monday morning, and then diminish to background levels from Tuesday to Wednesday. Wind wave driven surf heights along east facing shores will remain on the small choppy side through Tuesday, then increase slightly as trade wind speeds pickup by Wednesday. A very small northwest swell may pass through early next week, providing tiny surf along north facing shores on Monday and Tuesday before becoming nearly flat through the remain forecast period. && .FIRE WEATHER... Moderate to locally breezy trades will decrease slightly over the weekend before becoming locally breezy again next week. Despite the trade wind showers picking up across windward sections this weekend and early next week, afternoon relative humidities across leeward sections remain near summertime normals. Fairly typical fire weather conditions are expected. && .HFO WATCHES/WARNINGS/ADVISORIES... None. && $$ DISCUSSION...Pierce AVIATION...Pierce MARINE...Bohlin FIRE WEATHER...Pierce