Area Forecast Discussion
Issued by NWS Honolulu, HI
Issued by NWS Honolulu, HI
041 FXHW60 PHFO 311331 AFDHFO Area Forecast Discussion National Weather Service Honolulu HI 331 AM HST Fri May 31 2024 .SYNOPSIS... A high far northeast of the state will drive breezy to locally windy trade winds through the much of the forecast period. Showers will favor windward areas, becoming more prevalent at night. Upper troughing will move over the islands today 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 morning. Overnight soundings show a rather dry airmass, with 1.1 to 1.2 inches of PW. Increased stability is noted along with subsidence inversions between 5000 and 7000 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 later today 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 today 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 this weekend as a surface high moves closer to the state from the northeast. Clouds and showers will favor windward slopes with periodic MVFR conditions possible, especially during the overnight to early morning hours when an uptick in shower activity is expected. Otherwise, VFR conditions will generally prevail. Winds of 20 to 30 kts are expected to persist below an inversion between 5000 and 7000 feet. These conditions will maintain tempo moderate low level turbulence south through west of terrain, so AIRMET Tango remains in effect. AIRMET Sierra for mountain obscuration remains in effect across windward portions of the Big Island, Maui, Molokai and Oahu due to scattered showers riding in with the breezy to strong trades. These conditions are expected to improve later this morning as shower activity decreases. && .MARINE... Surface high pressure, centered around 1100 nm northeast of the area will maintain moderate to locally strong east- northeast trade winds through this afternoon. Winds will strengthen slightly to fresh to locally strong late today through the weekend as the high drifts south, tightening the pressure gradient. A Small Craft Advisory (SCA) remains for the typically windy waters around Maui and the Big island through this afternoon and has been expanded to nearly all remaining waters around Oahu and Kauai tonight through Saturday. The SCA will likely need to be extended through early next week due to the strengthening trades. A series of south swells will bring a prolonged period of above average surf along south facing shores through the start of June. Forerunners from the inital swell, roughly 1 foot 19 seconds out of the south, have been noted by the offshore buoys this morning. Guidance shows this swell slowly increasing through Saturday. Thus, surf along exposed south- facing shores will remain small this morning, but continue to rise slowly as the day progresses. The swell is expected to peak late Saturday into Sunday around 3 to 4 feet and generate surf near or just below the High Surf Advisory threshold of 10 feet. A reinforcing pulse should arrive on Monday and will likely maintain these surf heights. Surf 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 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 remain nearly flat to small 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 a 3 to 4 feet of swell from 320 degrees Monday into Tuesday. A broad extra tropical gale will track northeast then eastward off the coast of Japan 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 from 6 PM this evening to 6 PM HST Saturday for Kauai Northwest Waters-Kauai Leeward Waters-Kauai Channel- Oahu Windward Waters-Oahu Leeward Waters-Kaiwi Channel-Maui County Windward Waters. Small Craft Advisory until 6 PM HST Saturday for Maalaea Bay- Pailolo Channel-Alenuihaha Channel-Big Island Leeward Waters-Big Island Southeast Waters. && $$ DISCUSSION...Powell AVIATION...Farris MARINE...JT