The high pressure system north of Hawaii will slowly drift eastward as a low pressure system sets up north of the island chain by Friday. Moderate trade winds will continue a weakening trend producing hybrid trade wind and sea breeze wind flow each day lasting into early next week. Brief passing showers will drift into the islands on the easterly trade winds. Any showers will tend to favor windward mountain areas during the overnight to early morning hours. A more significant change to our weather pattern continues to evolve for early next week from Tuesday through Wednesday. Deeply unstable tropical moisture moving across the state will bring the potential for heavy rain and thunderstorms affecting all islands.
The satellite water vapor channel shows a weak upper level low over the state causing unsettled cloud bands to develop across the region, producing brief passing showers as these clouds are lifted up over windward mountain ranges. Drier diurnal weather trends remain in the forecast for the later morning to afternoon hours each day. Expect these conditions to continue through the weekend.
The high pressure system currently north of the state will slowly drift eastward away from the islands as a low pressure system takes its place just north of the Hawaii region. This pressure pattern change will weaken the large scale trade winds through the weekend, and allow a hybrid trade wind afternoon sea breeze wind flow to expand in coverage along the sheltered western mountain slopes of all islands.
A more significant change in our Hawaiian weather pattern is brewing from next week Tuesday onward as a large roughly 1,500 mile long band of deep tropical moisture advects northward over the islands. Expect warm and humid conditions during this time period due to the rising tide of tropical moisture. Global model solutions over the past three days are showing two or three weak cyclonic circulations embedded within this synoptic scale cloud band. Converging winds and upward motions surrounding these embedded lows will provide the forcing mechanism to produce stronger convective heavy rain bands and possibly thunderstorms. Some uncertainty remains in the forecast this far out and the forecast challenge with this pattern lies in predicting the arrival timing of this deeply unstable cloud band and predicting the intensity of these embedded low pressure systems and predicting their locations relative to the Hawaiian Islands. A medium confidence pattern for sure at this point with island by island weather impacts becoming clearer as the forecast time period grows shorter, and our global model solutions improve. Stay tuned.
A Hydrologic Outlook may be needed to cover the rising threats for heavy rain and flash flooding potential during this Tuesday to Wednesday time period. Please continue to closely monitor weather conditions, including the potential for flash flooding early next week as this weather pattern will likely evolve over time.
Generally VFR across all island airfields. A weak upper low over the state with vicinity surface troughs will create just enough instability, in tandem with ample lower level moisture, to maintain chances of prevailing VCSH and/or TEMPO SHRA with MVFR for lower ceilings over more windward-exposed terminals such as PHLI and PHTO.
No AIRMETS are in effect.
A surface low pressure system far north of the Hawaiian Islands will dig southeast, becoming located due north of the state by Friday. This will push the high pressure that has brought consistent trades off to the east. Trades will weaken through Friday, then weak to moderate trades are forecast this weekend into early next week. Forecast uncertainty increases beyond this point, as conditions across Hawaii will hinge on the uncertain evolution of a low pressure system developing west-southwest of the islands.
A small, medium-period northwest swell arriving this evening and overnight will provide a small boost to surf along north-facing shores on Friday. A moderate, medium-period north-northwest swell will follow this weekend, likely pushing surf to moderate levels beginning late on Saturday and peaking on Sunday. A storm-force low near Kamchatka will quickly follow this up with a moderate, long- period west-northwest swell maintaining moderate surf for north and west-facing shores early next week.
Surf along south-facing shores will remain small before a series of small to moderate, south-southwesterly swells boosts surf heights to near to above seasonal average this weekend into early next week.
East-facing shores will see trade-wind swell see a slight reduction in surf today as trade winds decrease, though a small, medium-period east swell originating from former Hurricane Trudy forecast to arrive today may help maintain east-facing surf into the weekend.
None.
