Area Forecast Discussion
Issued by NWS Honolulu, HI
Issued by NWS Honolulu, HI
592 FXHW60 PHFO 302010 AFDHFO Area Forecast Discussion National Weather Service Honolulu HI 1010 AM HST Thu May 30 2024 .SYNOPSIS... Surface high pressure far northeast of the islands will remain the impetus to breezy and locally windy trade winds. Drier weather will prevail the next couple of days. Isolated showers will favor windward areas and become more prevalent at night. Upper troughing to the northeast of the state will move over the area from Friday through the weekend. This will create a more unstable scenario and, with increasing moisture through the middle of next week, trade shower coverage and intensity will likely be on the rise. && .DISCUSSION... A 1031 mb surface high is centered approximately 1,400 miles northeast of Oahu in tandem with surface troughing located about 1,100 miles from Kauai. This is producing a tight enough pressure gradient back across the island chain to maintain breezy to locally windy trade winds. A drier air mass is advecting in from the east as evidenced in this morning`s local sounding pwats in the 1.1 to 1.3 inch range. A dry 850-700 mb layer, along with a stout near 5k ft inversion, will guarantee just isolated shower activity through Friday. Precipitation that does develop within the shallow boundary layer will be isolated in coverage and produce measurable accumulations of no more than a few tenths of an inch along windward-facing mauka slopes and coastlines. Mainly clear to partly cloudy/broken low cloud skies at lower elevations that will warm into the lower 80s (mid 60s to lower 70s at 6k ft elevation) will be the general rule both today and tomorrow. High pressure northeast of the state will settle more south- southeast as the trough of low pressure west of the area slowly lifts northward and washes out the next couple of days. This will hold a tight pressure gradient across the region this weekend to maintain or slightly boost breezy to locally windy (in gust) trades. Heights will lower over the state from Friday into the weekend. Extended NWP guidance is still a little out of phase on the location of this troughing. The EC solution keeps upper troughing out west as upper ridging builds in from east. This would equate to an uneventful, but slightly more wet, trade wind weather regime. The more bullish GFS is keeping the upper low/weakness over the islands longer and this would result in a more longer duration wet trade wind pattern. The emergence of the subtropical jet over or just south of the islands this weekend may offer more argument to a wetter early June pattern, all dependent on its positioning. Mid levels will remain fairly dry until Tuesday so this may weigh the forecast toward more dry. Regardless of any these minor model nuances, there is moderate confidence that next week`s upper troughing scenario will increase areal shower coverage and intensity...especially going into the middle of next week due to higher lower to mid layer moisture. && .AVIATION... Moderate to breezy trades will slightly strengthen this afternoon and remain breezy over the next several days. Mostly dry conditions this morning will give way to an increase of showers over the Big Island and windward Maui this afternoon and rest of the state tonight. Clouds and showers will favor windward slopes with brief MVFR conditions possible with the showers. VFR conditions will generally prevail across leeward areas. Soundings show a strong inversion between 5000 and 6000 ft. With the trades picking up a touch this afternoon, light to moderate low level turbulence will be possible south through west of any terrain. AIRMET TANGO will likely be needed this afternoon. Also with the increase of showers over the eastern half of the state this afternoon, AIRMET SIERRA may also be needed. With the showers expanding toward the rest of the state tonight, AIRMET SIERRA will be possible for other windward areas tonight. && .MARINE... High pressure centered far northeast of the area will maintain moderate to locally strong east-northeast trade winds today. Winds will strengthen slightly to fresh to locally strong Friday through the weekend as the high drifts south, tightening the gradient. The Small Craft Advisory for waters around Maui County and the Big Island has been trimmed back to just the typical windy waters into Friday. Additional zones around Oahu and Kauai waters will likely need to be included late Friday as winds strengthen. Surf along exposed south-facing shores will remain small through 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 from the first swell could arrive as early as Friday, build 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 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 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 Maalaea Bay- Pailolo Channel-Alenuihaha Channel-Big Island Leeward Waters-Big Island Southeast Waters. && $$ DISCUSSION...Blood AVIATION...Kino MARINE...Almanza