Area Forecast Discussion
Issued by NWS Honolulu, HI
Issued by NWS Honolulu, HI
522 FXHW60 PHFO 271345 AFDHFO Area Forecast Discussion National Weather Service Honolulu HI 345 AM HST Thu Jun 27 2024 .SYNOPSIS... Stable conditions under persistent breezy to locally windy trade winds will continue through the day. Light showers will generally focus along elevated windward exposures. The forecast passage of an upper level low north of the islands from Friday through the weekend may introduce increased shower activity and slightly increase isolated thunderstorm chances. && .DISCUSSION... The main story today will be of mainly continued dry and warm conditions. The large area of anchored high pressure centered approximately a 1,000 miles north northeast of Oahu will continue to drive breezy to locally windy trade winds through this afternoon. The high will subtly weaken tonight, relaxing the downstream pressure gradient enough to allow trades to fall to areawide gentle to locally breezy magnitudes from tonight through early Sunday morning. As in the past few days, light showers will generally produce low rain accumulation across more efficient convergent uplift areas such as smaller island windward-facing mauka slopes and the leeward Kona slopes of Big Island. This morning`s soundings are evidence that there isn`t much moisture to work with and this equates to another fairly dry day for many along coastal regions and leeward. Afternoon warmth may grow a deep enough partially-saturated boundary layer (under 800-850 mb) to pop a few more showers along most Big Island mauka regions and east Maui the next couple of afternoons. Yesterday afternoon`s local sounding profiles represented low 80 F convective temperatures. Depending on both an analogous pattern and the arrival timing of higher ribbons of eastern moisture, there may be an minor uptick in afternoon shower intensity and coverage today and Friday as we reach those daily low to mid 80s. While higher precipitation amounts will mainly stick to windward mauka slopes, occasional more organized cells will spill over into neighboring leeward communities. A broad cut off mid to upper level low is developing from troughing east of the state. Confidence is building that this low will meander northeast of the islands Friday and then track westward, passing north of the island chain this weekend. Decreasing stability in association with this low will likely enhance trade wind showers, particularly Saturday afternoon through Sunday. Isolated thunderstorms will be possible over Big Island slopes Friday and Saturday afternoon. The movement of the low and its relative proximity to the islands will ultimately determine the legitimacy of a storm threat. If the low tracks closer to Big Island Friday into Saturday, the coldest 500 mb temps closer to the low`s core could be the primarily player in initiating isolated Big Island mauka storms. However, with precipitable waters forecast to be near seasonal norms (around 1.3 inches) and no significant moisture advection anticipated, the amount of available moisture will certainly be the other limiting factor (to the upper low`s position in relation to the islands). After a weekend of lessened trades in response to the north- passing upper to mid level low, the low`s northwest exit Monday will end any enhanced shower or isolated storm threat. High pressure will reestablish itself north northwest of the state early next week. This translates to a return of a more traditional summertime trade weather pattern heading into July. && .AVIATION... Breezy trade winds will persist across the island chain today. Showers and low clouds riding in on the trades will bring brief periods of MVFR conditions over windward and mauka locations. Otherwise, VFR conditions will prevail. No AIRMETs are in effect at this time. However, AIRMET Sierra for tempo mountain obscuration may be needed later this morning if shower coverage increases. && .MARINE... High pressure north of the state will maintain moderate to at times strong trade winds through the weekend. A Small Craft Advisory (SCA) remains in effect for the typically windy waters around Maui and the Big Island through 6 PM this evening, and may be needed at times through the weekend as winds flirt with SCA levels. The trades look to strengthen back to fresh and strong levels early next week. A series of south swells will keep south shore surf near the summertime average through the weekend. Surf will lower below normal levels much of next week. A small northwest swell will fill in today, give a small boost to north shore surf on Friday, then fade out over the weekend. Typical mostly flat summertime conditions will prevail along north facing shores next week. East shore surf will remain well below normal through the weekend, then trend closer to seasonal levels next week as the trades strengthen over and upstream of the islands. && .HFO WATCHES/WARNINGS/ADVISORIES... Small Craft Advisory until 6 PM HST this evening for Maalaea Bay- Pailolo Channel-Alenuihaha Channel-Big Island Leeward Waters-Big Island Southeast Waters. && $$ DISCUSSION...Blood AVIATION...Farris MARINE...Jelsema