Area Forecast Discussion
Issued by NWS Honolulu, HI
Issued by NWS Honolulu, HI
254 FXHW60 PHFO 310640 AFDHFO Area Forecast Discussion National Weather Service Honolulu HI 840 PM HST Thu May 30 2024 .SYNOPSIS... A high far northeast of the state will drive breezy to locally windy trade winds through the remainder of the week. Showers will favor windward areas, becoming more prevalent at night. Upper troughing will move over the islands Friday into early next week, setting up periods of increased trade showers coverage and intensity. && .DISCUSSION... Surface troughing west of the main Hawaiian Islands, combined with high pressure far to the northeast, maintains a pressure gradient sufficiently steep to support moderate to breezy trade winds across local waters this evening. Afternoon soundings show variable airmass moisture, ranging from 1.1 to 1.6 inches of PW, with drier conditions noted on the Lihue sounding. Slight instability is noted along with subsidence inversions near 6000 feet. Radar shows isolated to scattered light showers within trade flow, embedded within patchy broken low clouds across windward areas depicted in satellite loops. Models show high pressure to our northeast will strengthen a bit and drift south-southeast as troughing to our west slowly lifts northward. This will provide a minor uptick in wind speeds into the weekend. The trough will wash out through the weekend as high pressure northeast of the state inches a bit southwestward and closer to the islands by the middle of next week, providing another slight boost to trades for the first few days of June. Models also show upper troughing will drift south across the islands Friday into next week, possibly increasing trade wind shower coverage and intensity. && .AVIATION... Breezy to locally strong easterly trade winds can be expected to increase slightly across the state this weekend as a surface high moves closer to the state from the northeast. Scattered showers currently moving over windward Big Island and windward Maui will spread up towards Oahu and Kauai tonight. Clouds and showers will favor windward slopes with periodic MVFR conditions possible, especially overnight when an uptick in shower activity is expected. Otherwise, VFR conditions will generally prevail across leeward areas. VAD wind profiles and soundings show winds of 20 to 30 kt below a strong inversion between 4500 and 6500 feet. Due to the strong winds below the inversion, AIRMET Tango remains in effect for moderate low level turbulence south through west of terrain and will likely be needed through Friday. AIRMET Sierra for mountain obscuration is also in effect tonight across windward portions of the Big Island, Maui and Molokai due to scattered showers riding in with the breezy to strong trades. This AIRMET may need to be expanded to include windward portions of the rest of the island chain later tonight as shower coverage increases. && .MARINE... Surface high pressure, centered around 1100 nm northeast of the area will maintain moderate to locally strong east- northeast trade winds tonight into Friday. Winds will strengthen slightly to fresh to locally strong late Friday through the weekend as the high drifts south, tightening the pressure gradient. A Small Craft Advisory (SCA) remain for the typically windy waters around Maui and the Big island through Friday afternoon. The SCA will likely need to be extended and expanded to include additional zones around Oahu and Kauai waters for Friday night through early next week due to the strengthening trades. Surf along exposed south-facing shores will remain small into Friday. A series of south swells will bring a prolonged period of above average surf along south facing shores through the start of June. Forerunners, roughly 1 foot 20 seconds out of the south southwest, have been noted by the outer buoys this evening. Guidance shows this swell slowly increasing during the day Friday, maintaining small surf through most of the day. The swell is expected to peak Saturday into Sunday around 3 feet. 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 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 and will likely increase slightly by this weekend. Surf along north-facing shores will continue to remain nearly flat over the next few days. A storm force low near Kamchatka should produce an out of season northwest swell that is expected to fill in late Sunday night into Monday. Latest guidance is showing 3 to 4 feet of swell from 320 degrees Monday into Tuesday. A small tropical storm tracking off the coast of Japan will transition into a broad extra tropical gale as it tracks north then eastward over the next couple of days. This system could bring a small reinforcing west- northwest to northwest swell Tuesday into the middle of next week. && .HFO WATCHES/WARNINGS/ADVISORIES... Small Craft Advisory until 6 PM HST Friday for Maalaea Bay- Pailolo Channel-Alenuihaha Channel-Big Island Leeward Waters-Big Island Southeast Waters. && $$ DISCUSSION...Powell AVIATION...Farris MARINE...JT