445 FXHW60 PHFO 221955 AFDHFO Area Forecast Discussion National Weather Service Honolulu HI 955 AM HST Sun Dec 22 2019 .SYNOPSIS... A high to the north will produce locally strong easterly trade winds today. The trades will focus showers over mainly windward areas. High clouds will keep skies gray, but will not bring any rain. Winds will shift out of the southeast tomorrow as a front approaches from the west. Breezy south winds and locally heavy rain will spread over Kauai and Oahu starting Tuesday. Winds and rain will subside on Thursday as the weakening front moves over Maui County and the Big Island. && .DISCUSSION... The 8 AM surface analysis shows a 1033 high centered far north of the area near 37N153W and a north to south trough about 800 miles to the west. The pressure difference between the high and trough is maintaining locally strong easterly trade winds over the islands. Because of the strong winds, a Wind Advisory is in effect for parts of Maui County and the Big Island of Hawaii. The trade winds are carrying some clouds and showers over mainly windward areas of the islands. Rainfall has decreased since yesterday as the shower band along the trailing end of a front has shifted south of the islands. Thick high clouds are spreading over the islands from the west. These clouds are not producing any rain, but they will keep skies gray, even over leeward areas. Over the next several days, the high to our north will move off to the east while the trough moves east and deepens. Winds over the islands will weaken and shift out of the southeast tomorrow. By Tuesday, winds will shift out the south (kona winds) around Kauai and Oahu and strengthen as a low deepens northwest of the area and a front forms west of the islands. Increasing moisture and instability will make heavy showers likely for Kauai and possibly Oahu and Maui County from Tuesday through Wednesday. The front will reach Kauai Wednesday. The computer models diverge by the end of next week. The GFS shows the front pushing down south of the Big Island by Friday night with trade winds building in behind the front. The European model shows the front stalling over the islands. && .AVIATION... Winds remain breezy this morning and several PIREPs continue to indicate that moderate turbulence is still occurring below 15,000 feet or so downwind of the mountains. Went ahead and updated AIRMET Tango to increase the height from 9,000 feet because of these reports. However, winds are still down from where they were 24 hours as the high generating these gusty conditions continues to weaken and move eastward. Winds will begin to shift out of the east-southeast overnight in response to a low moving towards the island chain from the west. Ahead of this next system, the atmosphere remains fairly stable and only a few showers are expected to impact mainly windward areas today. Ceilings have improved along windward slopes and coasts and will likely be able to cancel AIRMET Sierra for tempo mountain obscuration should this trend continue. Brief periods of MVFR conditions are still possible within heavier showers. Tempo light icing in the cloud deck over Kauai and Oahu is occurring between 150/FL240. && .MARINE... Strong high pressure north of the state will maintain strong to gale force winds over Hawaiian waters through this afternoon. A Gale Warning is in effect for the northwest Hawaiian offshore waters and the windier areas of the coastal waters around Maui and the Big Island of Hawaii. Winds are expected to be on a slow weakening trend over the next 24 hours as the high to our north fades. A front is expected to develop west of the state on Monday and gradually track eastward and toward the coastal waters. Models are in fairly good agreement with the front moving into the western coastal waters Tuesday night and the central coastal waters on Wednesday. Winds are expected to remain in the fresh to strong speeds through the first half of the week, but the wind direction will begin to veer from the southeast and south as front gets closer. Gusty winds and thunderstorms will be possible along the front Tuesday night into Wednesday. A High Surf Advisory remains in effect through tonight for east facing shores exposed to the strong trade winds. As the trade winds weaken, east shore surf will subside below advisory levels, but remain somewhat elevated and choppy. A series of small north and northwest swells will continue through next week, with surf heights expected to remain below the advisory threshold along north and west facing shores. No other significant swells are expected. Coastal flooding is expected this week as seasonal high tides coincide with breezy southerly winds ahead of the front. See Special Weather Statement (SPSHFO) on our website and the NOAA Tides and Currents website for more information. && .HFO WATCHES/WARNINGS/ADVISORIES... High Surf Advisory until 6 AM Monday for east facing shores of Kauai, Oahu, Molokai, Maui and the Big Island of Hawaii. Wind Advisory until 6 PM this evening for Molokai and Lanai, all of Maui except Haleakala summit and South Big Island, Big Island North and East and Kohala. Gale Warning until 6 PM this evening for Maalaea Bay, the Pailolo and Alenuihaha Channels and waters south of the Big Island. Small Craft Advisory until 6 AM Tuesday for Kauai Northwest Waters-Kauai Windward Waters-Oahu Windward Waters-Kaiwi Channel- Maui County Windward Waters-Maui County Leeward Waters-Big Island Windward Waters-Big Island Southeast Waters. Small Craft Advisory until 6 AM Monday for Kauai Leeward Waters- Kauai Channel-Oahu Leeward Waters. && $$ DISCUSSION...Donaldson AVIATION...Dye MARINE...Foster