Area Forecast Discussion
Issued by NWS Honolulu, HI
Issued by NWS Honolulu, HI
578 FXHW60 PHFO 211339 AFDHFO Area Forecast Discussion National Weather Service Honolulu HI 339 AM HST Fri Jun 21 2024 .SYNOPSIS... High pressure far north of the islands will maintain breezy and gusty trade winds through early next week. Passing showers will favor will favor windward slopes, especially during nights and mornings, with some light rainfall occasionally spreading leeward. && .DISCUSSION... A stable, breezy, and gusty trade wind flow remains in place, driven by strong high pressure sitting roughly 800 to 900 miles north of the state, and a robust mid-level ridge over the region is maintaining stable conditions with an inversion based between 5,000 and 7,000 feet. A narrow band of low-level moisture that moved through in the evening has largely cleared out, but another band of shallow moisture will move onto windward slopes this morning. A modest uptick in winds is due today as the high to the north builds slightly. This will lead to borderline Wind Advisory conditions the typically windy areas, such as the Maui Central Valley, portions of west Maui, the leeward areas of the Kohala Districts, the Humuula Saddle, Kau, and parts of the Hawaii Volcanoes National Park. The shallow moisture moving in will produce modest rainfall, with less than a quarter of an inch falling over most windward slopes today. With the exception of afternoon showers over the Kona slopes of the Big Island, leeward areas will experience little accumulation. Breezy trade winds and a typical summertime rainfall pattern will prevail this weekend into early next week. Modest showers will be focused over windward areas, mainly at night and in the morning. With the exception of afternoon and evening showers over the Kona slopes of the Big Island, leeward areas will be mostly dry. Trades look to decline to moderate levels Tuesday or Wednesday as the high to the north is weakened and displaced eastward. && .AVIATION... Breezy to locally windy trade winds will continue across the Hawaii region for the next few days. Brief passing showers are expected mainly over windward and mountain areas, favoring the overnight to early morning hours. AIRMET Sierra for mountain obscuration remains in effect for windward mountain slopes of Kauai, Oahu, Molokai, Maui, and Big Island. This AIRMET will likely diminish in coverage later this morning. AIRMET Tango remains in effect for moderate low level turbulence over and downwind of island mountains due to the breezy trade winds. && .MARINE... Strong easterly trades will continue into early next week, supporting the Small Craft Advisory in place for all waters. Seas have responded and will remain rough, with heights hovering around and just under the advisory level over exposed waters. Guidance shows a slight downward trend next week between Tuesday and midweek due to the surface ridge potentially weakening to the north. Surf along east-facing shores will remain rough through early next week due to the aforementioned strong trades locally and upstream of the state. Surf along south-facing shores will trend up to around average this weekend as a small south swell arrives. This should be short- lived, with a downward trend expected early next week. Despite a blocking high that has set up over our typical swell window near/southeast of New Zealand, guidance shows a gale forming to its northeast with the head of the fetch aimed at the islands around 2,500-2,700 nautical miles away within the 170 to 190-degree directional band. Given the shorter travel distance, surf could trend up late next week if this system materializes this weekend. Surf along north-facing shores could trend up above flat levels early next week due to a small, medium-period northwest swell from a marginal gale lifting northeastward toward the Aleutians today. On its heels is a compact storm-force low developing near Japan that could send a similar northwest swell through the area late next week. && .HFO WATCHES/WARNINGS/ADVISORIES... Small Craft Advisory until 6 PM HST Sunday for all Hawaiian waters. && $$ DISCUSSION...Wroe AVIATION...Bohlin MARINE...Gibbs