476 FXHW60 PHFO 201335 AFDHFO Area Forecast Discussion National Weather Service Honolulu HI 335 AM HST Sat Apr 20 2024 .SYNOPSIS... Moderate trade winds are forecast through the weekend with enhanced showers decreasing from west to east through this afternoon. Dry trade wind weather will continue on Sunday with wind speeds starting to pick up slightly by Sunday night as a high pressure system builds north of the islands. Brief periods of showers will pass through the islands through early next week in a moderate to breezy trade wind pattern. The middle of next week will be on the wet side for most islands, especially in the overnight to early morning hours, as a band of unstable clouds moves in from the northeast. && .DISCUSSION... Satellite imagery this morning shows a sharp upper trough moving into the northwest islands and a band of low clouds from an old frontal boundary at the surface level. This upper trough will help to enhance trade wind showers through the morning hours. An upper ridge will build in behind this trough as it passes from west to east across the state today, increasing stability and decreasing shower coverage. Sunday will be the most favorable weather day of the weekend for outdoor activities. Strong winds aloft enhanced by this passing upper level trough will continue to support High Wind Warning conditions for the highest Big Island summits of Mauna Kea and Mauna Loa until this evening. Winds at summit level will decrease quickly by around Sunset as the upper trough passes east of the Big Island. From Sunday night into Tuesday, a weak high pressure system will build just north of the Hawaiian islands. Fair weather remains in the forecast for most areas with a slight increase in our trade winds from moderate into the moderate to breezy range should be expected. One wrinkle in this forecast, no surprise to most locals, is the Hilo side of the Big Island and portions of East Maui will continue to see periods of enhanced showers. From Tuesday night into Thursday morning, a band of unstable clouds will move from northeast to southwest across all islands. Expect increasing shower trends, favoring windward and mountain areas especially in the overnight to early morning hours. Rainfall coverage was increased for this time period in the morning forecast grid package. From Thursday onward, typical trade wind weather will continue for the rest of the week with brief windward and mountain showers possible. && .AVIATION... Light to moderate trade winds will persist through forty-eight hours and beyond. Bands of low clouds and light showers off the Pacific will impact mainly windward slopes and coasts. Isolated spillover showers over leeward slopes of the smaller islands will taper off later this morning. Partial clearing expected over island interior's in the afternoon. AIRMET Sierra for mountain obscuration is currently in effect for windward portions of all islands. Conditions are expected to improve towards noon. && .MARINE... High pressure building in from the north-northwest will drift east and keep trade winds moderate to fresh through the weekend. The ridge of high pressure should rebuild early next week, which should produce fresh to locally strong trade winds once again. The current south swell will hold today than steadily decline Sunday. A series of small, medium period swells will persist through the weekend keeping south facing shores from going flat. Small, short- period north swell will continue into the weekend. A larger moderate medium period north swell reinforcement will arrive late tonight. A rise in surf overnight is expected but the north swell looks to peak Sunday well below High Surf Advisory levels. Surf along east facing shores will remain small but can expect a slight increase early next week as the trades strengthen. && .HFO WATCHES/WARNINGS/ADVISORIES... High Wind Warning until 6 PM HST this evening for Big Island Summits. && $$ DISCUSSION...Bohlin AVIATION...Bedal MARINE...Shigesato