793 FXHW60 PHFO 210631 AFDHFO Area Forecast Discussion National Weather Service Honolulu HI 831 PM HST Wed Nov 20 2019 .SYNOPSIS... A showery, wet and windy trade wind weather pattern is expected through the weekend. Showers will be most prevalent over windward and mauka areas, with the occasional leeward spill over. The trades are expected to ease next week. Trade wind showers will continue to focus over windward and mauka areas, with less leeward spillover. && .DISCUSSION... Currently at the surface, a 1030 mb high centered 1100 miles north-northeast of Honolulu, is driving moderate trade winds across the island chain this evening. Infrared satellite imagery shows clear to partly cloudy skies in leeward areas, with variably cloudy conditions in windward locales. Radar imagery shows scattered showers moving into windward areas, with a few shows drifting leeward from time to time. Main short term concern revolves around the strengthening trade winds. Model solutions are in good agreement showing a tight pressure gradient setting up across the island chain, between nearly stationary high pressure northeast of the islands and a trough of low pressure sliding by to the south. Breezy trade winds are expected to develop by Thursday, with breezy to windy conditions Thursday night through Sunday. The trades appear to peak in the Friday through Saturday time frame, and Wind Advisories may eventually be needed for some of the typically windier locations on the Big Island and Maui County. 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. As for weather details, we expect a showery wet trade wind pattern to hold through the weekend, as upper level troughing remains over the island chain. Showers will favor windward and mauka areas, but will also more regularly affect leeward locales due to the strength of the trades. Showers will be most prevalent during the overnight and early morning hours (between 6 pm and 10 am) each day. Forecast details become more uncertain for the first half 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, they disagree on the exact location where this feature will set up. Additionally, the model solutions have not shown the best run to run consistency. 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... Trade winds will strengthen overnight becoming breezy on Thursday. These stronger wind speeds will likely trigger issuance of AIRMET Tango by Thursday morning for moderate low level turbulence south through west of all island mountains. Otherwise mostly VFR conditions are forecast with brief periods of MVFR conditions developing mainly along windward slopes favoring the evening through early morning hours. No AIRMETs are currently in effect. AIRMET Tango for moderate low level turbulence will likely be issued with the Thursday morning forecast update. && .MARINE... Trade winds are back, and will continue to strengthen overnight into Thursday, becoming rather gusty and breezy, as a 1030 mb surface high lies 920 nm north-northeast of Oahu. Although the high will be moving east-northeast, further away from the islands during the next couple of days, it will also be strengthening and with a tight pressure gradient around the islands. So, the trades will be rather strong and gusty over the weekend area-wide, with near Gale-force winds in some of the channels. An anticipated northwest swell will be reaching the north and west facing shores of most of the islands later tonight. Deep ocean buoy 51001 had a reading of 12.5 feet swell at 7 pm HST and a period of 16 seconds. Buoy 51101, located just to the south of 51001, had a smaller reading of 10.5 feet and 16 seconds. Never- the-less, advisory level surf, possibly to near warning, is likely for Thursday. We will be monitoring the situation closely in the coming hours and make any necessary adjustment to the forecast. This northwest swell is expected to peak Thursday, followed by a gradual decline through Friday. With the trade wind and swell in mind, a Small Craft Advisory (SCA) is in effect for all near-shore waters, including recently added Maalaea Bay, where it is experiencing trade winds of 23 kt. The trade winds will favor the typical windy areas of Maui County and south of the Big Island. The incoming northwest swell will cover the rest of the near-shore waters. This SCA is good through late Friday afternoon, with the likelihood of an extension. This northwest swell will be reinforced by a moderate size swell Saturday into Sunday. This swell will then be followed by a smaller size swell on Wednesday of next week. With the significant boost in the trades into the weekend, the east facing shores may face a High Surf Advisory with surf 8 feet or higher. Lastly, a series of a small background southwest swells will maintain small surf along the south facing shores through the forecast period. && .HFO WATCHES/WARNINGS/ADVISORIES... High Surf Advisory until 6 AM HST Friday for Niihau-Kauai Windward-Kauai Leeward-Waianae Coast-Oahu North Shore-Oahu Koolau-Molokai-Maui Windward West-Maui Central Valley-Windward Haleakala. Small Craft Advisory until 6 PM HST Friday for all Hawaiian waters except Maalaea Bay- && $$ DISCUSSION...Jelsema AVIATION...Bohlin MARINE...Lau