Area Forecast Discussion
Issued by NWS Honolulu, HI
Issued by NWS Honolulu, HI
043 FXHW60 PHFO 300132 AFDHFO Area Forecast Discussion National Weather Service Honolulu HI 332 PM HST Wed May 29 2024 .SYNOPSIS... Surface high pressure far northeast of the state will maintain breezy to locally windy trade winds for the remainder of the week. Occasional shower activity will primarily be focused along windward slopes and coastlines, becoming more prevalent during the nocturnal hours. Upper level troughing northeast of the region will move over the islands from Friday into early next week. This set up will likely produce more frequent periods of increased trade showers in both coverage and intensity. && .DISCUSSION... A weak low within surface troughing are located approximately 700 nautical miles west-northwest of Kauai, along with a near 1034 mb surface high centered about 1,300 nautical miles northeast of Oahu. These are supporting a breezy to locally strong regional trade wind regime. The regional atmosphere was fairly moist with morning sounding pwats between 1.4 to 1.6 inches pushing the upper percentile of the late May climatological range. This relatively higher moisture within this breezy trade flow is mainly producing mainly scattered to broken mid level clouds, with occasional overcast windward mauka conditions, within a warmed inland air mass in the lower 80s. A quiet afternoon radar-wise with just isolated spotty showers. Other than Mt. Waialeale`s half of an inch today, the highest six hour rainfall of just a couple of tenths of an inch have been confined to the higher windward elevations. Better organized, deeper showers may drift over into the smaller island leeward communities. The main short to mid term forecast theme will center around daily rain chances and trade wind trends. A relatively mid to upper level drier air mass will travel across the state from the northeast through the weekend. This scenario will create a shallow near 5k ft inversion that will produce light windward slope and coastal showers that will become more frequent overnight. High pressure will slightly strengthen northeast of the state and settle more south-southeast as the trough of low pressure west of the area slowly lifts northward the next couple of days. This will provide a minor uptick of wind magnitudes as winds remain breezy to locally windy into early June. The trough will wash out through the weekend as high pressure northeast of the state inches a bit southwestward and closer to the island chain early to mid next week. This may provide a slight boost to trades the first few days of June. Heights will lower over the state from Friday into the weekend although extended NWP guidance is a little out of phase on the location of this troughing. The EC solution keeps upper troughing out west, upper ridging building in from east = basic trade wind weather pattern. The GFS is more bullish in keeping the upper low/weakness over the islands longer = more wet trade wind pattern. Regardless of these minor model nuances, there is moderate confidence that next week`s upper troughing scenario will increase areal shower coverage and intensity as lower to mid layer relative humidity increases over the state. && .AVIATION... Moderate to breezy easterly trades will continue for the next several days. Clouds and showers will favor wind ward slopes, where periods of MVFR CIGs/VSBYs will move through especially in the overnight and early morning hours. VFR conditions will prevail over most leeward areas, with the exception of afternoon and evening MVFR conditions over leeward Big Island. A mid-level ridge will maintain stable conditions with an inversion based between 6,000 to 8,000 ft. Easterly trade winds at and below the inversion level will remain in the 15 to 20 kt range, which will produce some low-level turbulence. It appears that AIRMET Tango will not be needed for these borderline conditions, though we will continue to monitor. && .MARINE... A trough northwest of the area and a high centered far northeast of the area will maintain moderate to locally strong easterly trade winds through tonight. As the trough weakens and drifts further away, the trade winds will slightly strengthen Thursday into Friday and back towards the east-northeast. Fresh to strong east-northeast trade winds should persist through the weekend as a ridge of high pressure remains anchored far north of the state. A Small Craft Advisory remains in effect for majority of the waters around Maui County and the Big Island through Friday and additional zones around Oahu and Kauai waters will likely need to be included by Friday. Surf along exposed south-facing shores will remain below the summer average (5 feet) through Friday. A series of south swells will move in over the weekend into next week and will likely bring a prolonged period of above average surf along south facing shores. Forerunners from the first swell could arrive as early as Friday, but should steadily fill in throughout the day Saturday and peak late Saturday into Sunday. A reinforcing pulse should arrive on Monday and will likely maintain surf heights near or just below the High Surf Advisory threshold of 10 feet. Surf heights should gradually trend down Tuesday through Wednesday as the south-southwest (200 degree) swell declines. A gale low currently developing just east of New Zealand, will likely bring another south (190 degree) swell Thursday into Friday of next week. Surf along exposed east-facing shores will continue to remain rough and choppy due to the windswell generated by the breezy trade winds. As the trades slightly strengthen Thursday into the weekend, we should see a slight increase of rough and choppy surf by this weekend. Surf along north-facing shores will continue to remain nearly flat over the next few days. A developing storm force low near Kamchatka should produce an out of season northwest swell, which should steadily fill in Sunday night into Monday. Latest guidance is showing 3 to 4 feet of swell from 320 degrees Monday into Tuesday. A typhoon tracking off the coast of Japan will likely bring a small reinforcing swell from the west-northwest to northwest Tuesday into the middle of next week. && .HFO WATCHES/WARNINGS/ADVISORIES... Small Craft Advisory until 6 PM HST Friday for Kaiwi Channel- Maui County Windward Waters-Maalaea Bay-Pailolo Channel- Alenuihaha Channel-Big Island Leeward Waters-Big Island Southeast Waters. && $$ DISCUSSION...Blood AVIATION...Wroe MARINE...Kino