196 FXHW60 PHFO 220633 AFDHFO Area Forecast Discussion National Weather Service Honolulu HI 833 PM HST Wed Aug 21 2019 .SYNOPSIS... Trade winds will weaken briefly Thursday night through early Saturday, then return to the moderate to breezy range late Saturday through the second half of the weekend. Clouds and showers will favor windward and mountain locations, especially through the overnight and early morning periods as pockets of higher moisture move through. The exception will be over the leeward areas of the Big Island, where afternoon and evening clouds and showers form in response to the local sea breeze. Warm and humid conditions will become a possibility Tuesday through Wednesday as the trades trend down into the light and variable range. && .DISCUSSION... The latest surface analysis showed a weakness within the subtropical due to an upper low and dissipating surface trough several hundred miles north to northeast of the islands. Despite this weakness, breezy trades are holding over the islands. Clouds and showers are focusing over the typical windward and mountain locations. Rainfall accumulations have remained light over the past six hours (through 7 PM HST), ranging from a few hundredths over the smaller islands to just under half of an inch over the Big Island. The afternoon upper air soundings at Lihue and Hilo reflected this showing plenty of mid- to upper-level dry air in place above a strong subsidence inversion positioned between 5,000 and 6,500 ft. Precipitable water (PW) values were around the seasonal average from both soundings (around 1.4 inches). The short-term guidance remains in good agreement and depicts the trades trending down into the light to moderate range late Thursday through early Saturday as the aforementioned upper low and surface trough pass to the north from east to west. An upward trend in windward shower coverage can't be ruled over Kauai Thursday night into Friday as the moisture axis associated with the trough moves through (PWs near two inches). Elsewhere, mostly dry conditions will prevail with clouds and showers favoring windward and mountain locations. Moderate to breezy trades will return over the weekend as the upper low and surface trough continue westward and high pressure builds to the north. An increase in shower coverage will be possible late Saturday into Sunday as a pocket of higher moisture moves through from east to west. Model PWs within this pocket of higher moisture climb into the 1.75 to 1.9 inch range over the Big Island late Saturday, then to the smaller islands Saturday night into Sunday. For the extended, guidance remains in decent agreement through the first half of the week and shows a weakness developing within the ridge as a broad upper trough and surface front pass to the north. The pressure gradient is forecast to respond and weaken over the state, which could be enough for a land and sea breeze regime to become established Tuesday through midweek. If this scenario evolves, clouds and showers will favor interior areas through the afternoon and evening periods. && .AVIATION... VFR conditions are expected to prevail, with some brief MVFR conditions possible over the windward areas with passing clouds and showers. High pressure north of the islands will maintain moderate to locally breezy trade winds overnight and into tomorrow. AIRMET Tango remains posted tonight for mechanical turbulence to the lee of the mountains. A weakening in the pressure gradient over the islands tonight will lead to a weakening in the trade wind pattern. As such, expecting AIRMET TANGO to be dropped at some point on Thursday. && .MARINE... High pressure to the northwest will maintain mostly moderate to fresh trades through Friday. The typical windy areas around Maui and the Big Island will continue to see locally strong trades through Thursday. Thus, a Small Craft Advisory (SCA) remains in effect for the typically windy waters around Maui and the Big Island. A front moving southward toward the island chain over the next 24 hours will ease the trade winds Thursday night through Friday. A new high building northeast of the islands will then strengthen the trades back to moderate and locally strong levels over the weekend, with SCAs likely being required once again for the windier marine zones. The current long-period south swell will hold steady through tonight, then gradually lower Thursday and into the weekend. A High Surf Advisory remains in effect for south facing shores of all islands through 6 AM Thursday. A series of small long-period south and southwest swells will move through Sunday through early next week. A larger southwest swell is possible Tuesday through the middle of next week. Small northwest swells will linger over the next few days providing some out of season surf along north facing shores. Trades will continue to produce small choppy surf along east facing shores over the next few days. An increase in wind swell is expected late in the weekend as trades strengthen locally and upstream of the state. && .HFO WATCHES/WARNINGS/ADVISORIES... High Surf Advisory until 6 AM HST Thursday for Niihau-Kauai Windward-Kauai Leeward-Oahu South Shore-Waianae Coast-Molokai Leeward-Lanai Makai-Kahoolawe-Maui Leeward West-Maui Central Valley-Leeward Haleakala-Kona-South Big Island-Big Island North and East. Small Craft Advisory until 6 PM HST Thursday for Maalaea Bay- Pailolo Channel-Alenuihaha Channel-Big Island Leeward Waters-Big Island Southeast Waters. && $$ DISCUSSION...Gibbs AVIATION...M Ballard MARINE...Kino