332 FXHW60 PHFO 100635 AFDHFO Area Forecast Discussion National Weather Service Honolulu HI 835 PM HST Thu Jan 9 2020 .SYNOPSIS... An increase in showers is expected tonight through Saturday as an upper trough slowly approaches the state from the east. Periods of heavier rainfall will be possible, especially over windward and mauka areas, but the windy trades should keep the showers moving fairly quickly. Winds are expected to slightly decrease later in the weekend and gradually shift out of the east-southeast as a trough develops west of the state early next week. This could lead to more unsettled weather especially for the western half of the state during the first half of next week. && .DISCUSSION... Strong high pressure north of the state will maintain strong and gusty trades through Friday with a slight decrease expected over the weekend. Aloft, we have an upper level trough northeast of the state and is expected to track west and pass near the state during the next few days. This will lead to an enhancement of trade wind showers beginning tonight over Maui and Big Island and spreading west towards Oahu and Kauai later tonight into Friday. Latest radar and satellite imagery continue to show frequent showers over windward and mauka areas of Maui and the Big Island with rainfall rates averaging about 0.5 inches to 1 inch per hour. This wet and showery rainfall pattern will continue through Saturday with pockets of heavier rainfall at times as the trough passes near the state. Due to the unsettled weather pattern, a Flash Flood Watch remains in effect for Maui and the Big Island through Saturday afternoon. A Flash Flood Watch will be certainly possible for Oahu and Kauai Friday into Saturday, but at this time it is looking like the the strong winds will keep the showers moving, thus limiting the Flash Flood potential. The Wind Advisory for the lower elevations of Oahu, the islands in Maui County, and the Big Island, is in effect through tonight, but may be extended through Friday. And a Winter Weather Advisory is in effect for light snow accumulations over the Big Island summits through Friday night. Breezy trades will begin to ease Saturday night. On Sunday, models show the upper trough just west of Kauai along with an induced surface trough west through southwest of Kauai. The surface trough will cause winds to shift slightly south of east over the western half of island chain and pull unsettled weather northwestward over the island chain. This unsettled weather may last into the middle of next week. && .AVIATION... Windy and wet trade wind weather will continue during the next 24 hours, bringing widespread showers and MVFR cigs/vsbys to windward areas, and passing showers with some reduced cigs/vsbys in leeward locales. AIRMET Sierra remains in effect for mountain obscuration across windward sections of Kauai, Oahu, Molokai, Maui and the Big Island. AIRMET Tango remains in effect for low level turbulence over and downwind of the terrain, as well as for strong surface winds. && .MARINE... A strong high pressure system is expected to remain northeast of the state into next week, and will continue to have a significant impact on our marine interests. Strong to gale force winds will continue through Friday, with a gradual downward trend possible Friday night. Those areas under a Gale Warning will go to a Small Craft Advisory (SCA) as winds drop below gale levels due to a combination winds and elevated seas. The elevated seas are due to the fetch generated by this high pressure system. Winds and seas are expected to remain above SCA levels over most marine areas at least into the middle of the new week. Winds will gradually veer to the east-southeast early next week as a trough develops to the west of the islands. As an upper level feature moves over the islands from the west tonight and remains overhead into the weekend, a more unstable airmass will bring the chance for locally heavy downpours and a risk for thunderstorms. The above mentioned fetch is also generating warning level surf along the east facing shores. The High Surf Warning is in effect through Saturday, but the surf will remain elevated at advisory levels into the middle of the new week. Over the next few days, the combination of the large surf, strong onshore winds, high astronomical tides, and elevated ocean water levels will produce wave runup and localized coastal erosion along east facing shores. A long-period northwest swell arriving late tonight into Friday could produce surf around the advisory level Friday night into Saturday. A smaller northwest swell is expected to fill in Sunday and gradually decrease early next week. && .HFO WATCHES/WARNINGS/ADVISORIES... Wind Advisory until 6 AM HST Friday for Oahu South Shore-Waianae Coast-Oahu Koolau-Waianae Mountains-Molokai-Lanai-Kahoolawe-Maui Windward West-Maui Leeward West-Maui Central Valley-Windward Haleakala-Leeward Haleakala-South Big Island-Big Island North and East-Kohala-Big Island Interior. High Surf Warning until 6 PM HST Saturday for Kauai Windward- Oahu Koolau-Olomana-Molokai Windward-Maui Windward West-Windward Haleakala-South Big Island-Big Island North and East. Flash Flood Watch through Saturday afternoon for Maui-Kona-South Big Island-Big Island North and East-Kohala-Big Island Interior. Winter Weather Advisory until 6 AM HST Saturday for Big Island Summits. Gale Warning until 6 AM HST Friday for Kaiwi Channel-Maalaea Bay- Big Island Leeward Waters-Big Island Southeast Waters. Small Craft Advisory until 6 PM HST Sunday for Kauai Northwest Waters-Kauai Windward Waters-Kauai Leeward Waters-Kauai Channel- Oahu Windward Waters-Oahu Leeward Waters-Maui County Windward Waters-Maui County Leeward Waters-Big Island Windward Waters. Gale Warning until 6 PM HST Friday for Pailolo Channel- Alenuihaha Channel. && $$ DISCUSSION...Kino/Gibbs AVIATION...Jelsema MARINE...M Ballard