| Current Conditions | ||
| Temp |  | 3.6 C |
| RH | | 70 % |
| Wind | | NE 11 mph |
| Road | | Closed |
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Hawaiian Islands Synoptic Discussion and Guidance 492 FXHW60 PHFO 211959 AFDHFO Area Forecast Discussion National Weather Service Honolulu HI 959 AM HST Thu Nov 21 2019 .SYNOPSIS... Trade winds will strengthen Friday and will bring windy and showery weather through Saturday. Showers will be most prevalent over windward and mauka areas, with showers spilling over into leeward communities from time to time. The trades are expected to ease a bit next week. Trade wind showers will continue to focus over windward and mauka areas, with less shower activity reaching leeward locales. && .DISCUSSION... Latest radar and satellite imagery is showing numerous showers this morning over windward and mauka areas with scattered showers over leeward areas. Cloud tops of up to 40,000 feet have been observed north and northeast of the state. Due to the elevated cloud tops and numerous showers upstream of the state, the forecast has been updated to increase shower coverage and to include slight chance of thunderstorms over Kauai for today. For tonight, breezy and showery conditions will likely continue across the state as another band of clouds moves through the state. Starting Friday, models are in good agreement with the pressure gradient tightening across the state. Trade winds are expected to strengthen and confidence is increasing for wind speeds to reach wind advisory criteria across many areas through Saturday. The weekend should remain windy and showery on Saturday, with a slight decrease of winds and shower coverage possible on Sunday. We should see the trades ease and shift around to more of an east-southeasterly direction during the first half of next week, as a trough of low pressure sets up several hundred miles west of the state. Moderate to breezy trades will likely hold in place across windward sections of the Big Island and Maui, with light to moderate trades expected elsewhere, lightest in leeward locales. Forecast details become more uncertain towards the middle of next week. Although both the GFS and ECMWF are in good agreement that a trough of low pressure will develop west of the state, and have come into better agreement with respect to the location where the trough will set up for the 00Z runs, run to run consistency has shown some significant deviations which will have a considerable impact on the weather we see locally. For now and until details become more clear, the forecast will reflect a trade wind shower pattern favoring windward and mauka showers and the occasional leeward spillover through the extended portions of the forecast. && .AVIATION... Strengthening surface high pressure northeast of the state will bring breezy east northeast trades winds through the remainder of today. Areas of enhanced moisture caught up in the flow, combined with weak instability, will generate scattered showers mainly along the windward coasts and slopes. MVFR conditions may occur with mountain obscuration from low ceilings and decreased visibility. A few showers could make it over the mountainous terrain and on the leeward areas. AIRMET Sierra remains in effect for north thru east sides of Maui, Molokai, and Oahu above 2000 feet due to mountain obscuration from clouds and showers. AIRMET Tango remains in effect over and immediately south thru west of mountains on all islands below 8000 feet due to tempo moderate turbulence. && .MARINE... Trade winds will continue to strengthen today and tonight with speeds reaching near gale force in some of the channels Friday through and Saturday due to a strengthening surface high far northeast of the area. A Small Craft Advisory (SCA) is currently in effect for all Hawaiian waters, due to the large northwest swell and/or locally strong trades and rough, choppy seas that will continue to increase tonight. This SCA, in effect until 6 pm HST Friday, is likely to be extended through the weekend. The northwest swell has arrived, with buoy 51001 peaking at 14 feet yesterday evening with a 16 second period. It is currently on the way down, but because this swell is running up to 4 feet higher than Wave Watch, a High Surf Warning was issued for north and west shores of Kauai and Oahu, while a High Surf Advisory (HSA) continues for north and west Molokai and north facing Maui shores through 6 PM this evening. There is enough of a west component to this swell where the southern half of the Big Island coastline will be affected, so an HSA is now in effect through 6 AM, followed by a gradual decline through Friday. A reinforcing, moderate northwest swell will fill in this weekend, followed by a smaller northwest swell arriving Wednesday of next week. As a result of the strong trades, east facing shores of most islands will see advisory level surf over the weekend. Lastly, a series of a small background southwest swell will maintain small surf along south facing shores through the forecast period. && .HFO WATCHES/WARNINGS/ADVISORIES... High Surf Warning until 6 PM HST this evening for Niihau-Kauai Windward-Kauai Leeward-Waianae Coast-Oahu North Shore-Oahu Koolau. High Surf Advisory until 6 AM HST Friday for Molokai-Maui Windward West-Maui Central Valley-Windward Haleakala-Kona. Small Craft Advisory until 6 PM HST Friday for all Hawaiian waters. && $$ DISCUSSION...Kino/Wroe AVIATION...Thomas MARINE...TS Bulletins, Forecasts and Observations are courtesy of Honolulu National Weather Service Forecast Office |
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