992 FXHW60 PHFO 010159 AFDHFO Area Forecast Discussion National Weather Service Honolulu HI 359 PM HST Fri Mar 31 2023 .SYNOPSIS... Widespread mid to upper level clouds will be on the increase tonight with mostly cloudy skies expected on Saturday. Showers will be on the increase Sunday as an upper level trough develops over the state. Trade winds will fill back in across the western half of the state by late Sunday with breezy trades expected across the state by Tuesday. A showery trade wind regime is expected during the first half of next week. && .DISCUSSION... Afternoon satellite and radar imagery shows pockets of heavy showers and isolated thunderstorms along the surface trough boundary on Kauai and its surrounding waters. These showers and isolated thunderstorms should decline in intensity this evening, but some locally heavy downpours will still be possible through tonight. Another short-wave trough approaching the area tonight is already starting to produce showers and thunderstorms roughly 200 miles west to southwest of the state. As this trough moves closer to the state on Saturday, it will begin to lose it upper level support and the showers and isolated thunderstorms are expected to stay just west of the state, but it will bring an increase of mid level and high clouds across the state with mostly cloudy skies expected. The cloud cover should help keep shower intensities on the lighter side with some moderate showers possible especially on Kauai for Saturday. Starting Sunday, a broad upper level trough will begin to develop over the state and will bring an increase of showers and possibly thunderstorms across the state. With trades starting to fill back in over the western end of the state, windward areas could become quite showery Sunday afternoon through Monday. Trade winds will further strengthen and become breezy by Tuesday as a ridge of high pressure becomes well established across the north Pacific. With the upper level trough lingering near the state through the first half of next week, showery trade wind weather is expected over windward areas with showers spilling over to leeward areas at times. && .AVIATION... A low pressure system with an associated trough far northwest of Kauai will continue to bring enhanced showers and isolated thunderstorms to Kauai and portions of Oahu through tonight. Periods of MVFR ceilings and visibility may accompany some of the heavier showers and storms. AIRMET Sierra is in effect for mountain obscuration for Kauai and Oahu due to low clouds and showers, and will likely continue through tonight for portions of those islands. Elsewhere, Light east-southeast flow west of Maui will allow mainly isolated sea breeze showers to continue over interior and leeward areas into this evening, before land breezes take over tonight and disperse them. AIRMET Tango is also in effect for tempo moderate turbulence in the layer FL200-FL350 due to a jet streak passing over the state. The latest Ellrod Index guidance supports these conditions continuing into Saturday. && .MARINE... A weak high pressure ridge near Maui County and a low pressure trough west of Kauai has been nearly stationary. This pattern has resulted in a veering of the surface winds from easterlies near the Big Island to southeasterlies over Kauai. The trough is forecast to remain nearly stationary through Saturday, then drift slowly westward on Sunday through early next week. This will allow the trade winds to fill in westward over the rest of coastal and offshore waters. Winds across the east end of the state were strong enough to warrant a Small Craft Advisory (SCA) for the normally windier areas around the Big Island. A low pressure system aloft has also created conditions unstable enough to support thunderstorm activity over the coastal waters near Kauai. This area of instability should remain in place through Saturday, then expand eastward over the remaining waters on Sunday as a new low pressure system aloft develops just northeast of the state. The current small northwest (320 degrees) swell will slowly decline through Saturday. A small northeast swell has reached the nearshore buoys and is expected to fill in tonight, peak Saturday, then decline on Sunday. There are no other significant swells in the North Pacific expected to affect the main Hawaiian Islands through late next week. Fresh trades upstream of the state will continue to produce near to slightly below normal surf along east facing shores during the next 7 days. Small background energy from the southwest, south and southeast will continue to produce small surf along south facing shores through late next week. && .HFO WATCHES/WARNINGS/ADVISORIES... Small Craft Advisory until 6 PM HST Saturday for Alenuihaha Channel-Big Island Windward Waters-Big Island Leeward Waters-Big Island Southeast Waters. && $$ DISCUSSION...Kino AVIATION...TS MARINE...Kodama