746 FXHW60 PHFO 132011 AFDHFO Area Forecast Discussion National Weather Service Honolulu HI 1011 AM HST Fri Dec 13 2019 .SYNOPSIS... Breezy to locally windy trade winds are expected today as strong high pressure passes well to our north. The trades will bring rainfall to mostly windward and mauka locales, with a few showers briefly reaching leeward. The high level jet stream will bring increasing high clouds later today into tonight. Trade winds will decrease during the weekend as the high moves away. A dry, stable airmass will take control of our weather this weekend and the first half of next week, with few showers and considerable sunshine. A new high passing far to the north will return locally windy trades Monday and Tuesday. && .DISCUSSION... The stationary front that was just NW of Kauai is beginning to retreat westward away from the islands as a surface trough. This is allowing breezy to locally windy trades to return as a surface high passes about 900 miles N of the islands today. An upper trough just W of the islands has been helping to reinforce the front, and enhance incoming trade wind showers. The upper trough is expected to weaken as we head into the weekend, which will result in fewer and less intense showers. High level moisture riding in on the subtropical jet will continue to bring high clouds at times, and these will increase tonight into Saturday before pushing away later Saturday as the jet shifts to the SE of the islands. The surface high to the N will continue eastward into the weekend, so trade wind speeds on Saturday will be a notch below today's levels. Winds will even be a notch lower on Sunday as a col between two highs passes N of the islands. The next surface high will pass well N of the islands on Monday, returning breezy to locally windy trade wind speeds for Mon and Tue. The winds should ease Wed, but may increase again on Thu as the next in the series of highs passing to the N approaches our longitude. Trade wind showers are expected to continue to decrease as we head into the weekend, with decreasing precipitable water and warming mid-level temperatures. A strong 700 mb high just to our N will bring warm mid-level air early next week. This, combined with a lack of moisture, should yield a significant minimum in trade wind showers Tue and Wed, with nice fine weather expected. Showers may increase again Thu as the mid-level high moves away and the airmass becomes a bit more unstable again. && .AVIATION... An area of enhanced moisture continues to reside over the islands this morning in a association with a dissipating front. Greatest coverage of showers will remain over mainly interior/windward areas of Oahu and Kauai as well as windward areas of the remaining islands. Brief MVFR conditions and mountain obscuration may occur due to the passing showers. Surface high pressure to the northeast of the state will allow for moderate to occasionally breezy easterly trades to persist through the period. No AIRMETs are currently in effect. && .MARINE... The current northwest swell will continue to subside from west to east over the next few days. The High Surf Advisory remains posted for north and west facing shores of Kauai County, Oahu, and Molokai and north facing shores of Maui. Surf is expected to fall below advisory levels by early tomorrow morning. A short period north-northeast swell will increase surf along exposed east facing shores, mainly on Kauai and Oahu, today and tonight, but should stay just below the advisory levels. A reinforcing large northwest swell is forecast to build late Sunday into Monday and peak Monday night, possibly near warning levels. This swell should slowly decline Tuesday into Wednesday, but will likely be reinforced by another large northwest swell Wednesday night into Thursday. A high pressure north of the state will keep moderate to locally strong trade winds over the area through Saturday. The combination of the current northwest swell and the strong trade winds is resulting in a Small Craft Advisory for all coastal waters, except the Maui leeward waters. This Small Craft configuration is expected to be trimmed down to mainly the locally windier waters around the Big Island and Maui County by tomorrow morning as the swell subsides. A slight decline in trade winds and period without Small Craft conditions is possible Sunday as the current high moves east and a new high builds north. Trade winds should return to moderate to locally strong speeds by early next week and seas will build with the reinforcing northwest swell. && .HFO WATCHES/WARNINGS/ADVISORIES... High Surf Advisory until 6 AM HST Saturday for N and W facing shores of Niihau, Kauai, Oahu, Molokai, and N facing shores of Maui. Small Craft Advisory until 6 AM HST Saturday for all Hawaiian Coastal Waters except for Maui County Leeward Waters. && $$ DISCUSSION...R Ballard AVIATION...Thomas MARINE...EATON