Area Forecast Discussion
Issued by NWS Honolulu, HI
Issued by NWS Honolulu, HI
328 FXHW60 PHFO 171344 AFDHFO Area Forecast Discussion National Weather Service Honolulu HI 344 AM HST Sat May 17 2025 .SYNOPSIS... A complex upper-level low over the islands will produce unsettled weather with moderate wet trades prevailing for the next several days. Heaviest showers will impact primarily windward and mountain areas, though leeward sides may also see brief periods of showers. Expect only slight variations in shower activity throughout the forecast period. && .DISCUSSION... The latest water vapor imagery coincides with model guidance showcasing a complex upper-level low centered over the islands producing unsettled weather across the region. The upper-level soundings from this morning`s 2 AM HST (12z) balloon launch at Hilo and Lihue demonstrates that the temperature inversion sits at around 10,000 feet and near 8,000 feet respectively, allowing for continued bands of showers to rummage through the state, especially in the vicinity of Kauai and Oahu this morning. While the heaviest showers will mainly impact the windward and mountain portions of the islands, brief periods of leeward side showers cannot be ruled out. Current satellite imagery displays another band of showers and clouds is approaching the islands from the east over the next several hours, however this cloud band will likely only impact the smaller islands from the late morning into the afternoon hours. Otherwise weather impacts on Saturday will hold very similar traits with only subtle wind direction shifts veering a bit more from the ESE direction while decreasing in strength over the weekend. While showers remain slightly pulse-y this morning, anticipate more organized plumes of mostly light to locally moderate rain this afternoon. The previously mentioned complex upper-level low remains quasi- stationary throughout the weekend and into next week with only slight variations in day by day shower activity across the island chain. Trades are expected to decrease slightly to more moderate levels from Saturday onward into early next week. Shower trends will also decrease in coverage a bit from Sunday to Tuesday across most islands as the upper low briefly weakens. Another upper low moves in over the islands on Wednesday with increasing shower trends for the second half of next week. && .AVIATION... Moderate to locally breezy trades will decrease slightly this weekend, with an upper-level disturbance enhancing shower activity primarily for windward and mountain portions of the island chain. Expect VFR condition to prevail for most locations, with periods of MVFR conditions to remain possible in any showers. AIRMET Sierra remains in effect this morning for mountain obscuration along northern through eastern sections of Kauai. && .MARINE... Strong high pressure will remain anchored northeast of the state through early next week. A developing trough to the distant northwest is expected to ease the trades tonight into early next week. Light to moderate trades are expected through the middle of next week over the western islands, while moderate to fresh trades are likely to persist over the eastern end of the state. A Small Craft Advisory (SCA) has been scaled back this morning to the windier waters around Maui and the Big Island through 6 pm today. Surf along north and west-facing shores will remain very small during the next 7 days. Surf along south-facing shores will hold at background levels through today. A series of small south and south-southwest swells will give a small boost to south shore surf Sunday with a further boost up to the seasonal average possible during the middle to latter part of next week. Surf along east-facing shores will hold close to seasonal normals during the next 7 days. && .HFO WATCHES/WARNINGS/ADVISORIES... Small Craft Advisory until 6 PM HST this evening for windier waters and channels around Maui and Big Island. && $$ DISCUSSION...Pierce/Bohlin AVIATION...Pierce/Bohlin MARINE...Shigesato