Area Forecast Discussion
Issued by NWS Honolulu, HI
Issued by NWS Honolulu, HI
224 FXHW60 PHFO 180658 AFDHFO Area Forecast Discussion National Weather Service Honolulu HI 858 PM HST Fri May 17 2024 .SYNOPSIS... A kona low northwest of the state will continue drawing unstable tropical moisture northward over Kauai County through Saturday. The kona low will begin slowly drift north away from the state this weekend with improving trends spreading from east to west, though enhanced rainfall may linger over Kauai and Niihau through Saturday night. By Monday all islands will see an improvement in weather conditions as easterly trade winds return. && .DISCUSSION... A kona low remains centered roughly 750 nm northwest of Kauai and a trough orientated northeast to southwest near Kauai. Latest satellite imagery shows a broad broken cloud band extending from the northeast to southeast over Kauai and Oahu and some mid- level and high clouds streaming from west to east over the rest of the island chain. Radar imagery earlier this evening showed the rainband that brought significant rainfall to Oahu Thursday and earlier this morning has quickly moved north of Kauai with some rainfall gauges picking up over a quarter of an inch an hour. Currently radar imagery shows rainfall activity has quited down with scattered moderate to light showers building along the Koolau range this evening and moving from the south to north near Kauai. The Flood Watch for Kauai County remains in effect through Saturday night as hi-res models continue to show a possibility for heavy rainfall to build back east over Kauai Saturday morning. The main consideration for the island of Kauai continues to be how long the band lingers over the island before moving off to the northwest as the kona low exits the region. While consensus is that conditions will begin to improve Saturday night, the flooding concerns could linger a bit longer should this be a slower transition. Models also are still hinting that one last moisture surge back towards Oahu is possible on Saturday night, but confidence remains low in this occurring at this time. High pressure will slowly build into the region this weekend as the kona low exits the pattern to the north. Expect more stabilizing trends with decreasing showers as east to southeast winds spread across the state. Likely by Sunday, the moderate to heavy rainfall threat will diminish over Kauai as more stable conditions fill in across the state. More typical easterly trade winds will return across the state from Monday onward with only brief passing showers in the forecast favoring the typical windward and mountain areas through the middle of next week. && .AVIATION... An unstable tropical environment with a low level trough over Kauai will keep MVFR conditions with brief IFR conditions possible in moderate to locally heavy showers lasting into Saturday. Lingering instability near Oahu will keep periods of MVFR conditions in showers favoring the eastern slopes. Most islands will see light large scale southeast to south winds interacting with overnight land and daytime sea breezes over each island through the weekend. Clouds and showers will build over island mountain and interior sections during the day with some clearing at night for most islands. Kauai will be the exception to this rule as a low level trough will enhance clouds and showers for the next 24 hours. AIRMET Sierra in effect for mountain obscurations over Kauai, Oahu, and the eastern slopes of the Big Island. Occasional light rime icing is expected from Kauai to Oahu in layer 140-FL250. && .MARINE... Fresh to locally strong south to southeast winds associated with a kona low north-northwest of the state will persist into Saturday. A shift out of the east to southeast direction is expected over the weekend through early next week as it lifts northward and away from the area and the ridge begins to build north of the area. A Small Craft Advisory remains in effect for the Windward and Leeward Big Island waters (Hamakua Coast and waters near South Point) through early Saturday. As we trend back to a more typical trade wind pattern by the end of the weekend, a SCA may be needed for the windier locations around Maui County and the Big Island. Surf along south facing shores will remain up through early next week due to overlapping, long-period south-southwest swells. The first swell that peaked today will hold around the advisory level into Saturday before briefly lowering. The short-period wind chop added from the southerly winds will linger into Saturday, then ease as we transition back to an east to southeast wind regime by Sunday. This will translate to cleaner surf conditions. A fresh, long-period south-southwest swell will fill in through the day Sunday, then peak slightly lower than the current swell early next week before easing Tuesday through midweek. Surf along north facing shores will steadily lower through the weekend, with a return to a more typical pattern for this time of year next week. Surf along east facing shores will remain well below average through the weekend. An upward trend is possible next week as the trades return locally and far upstream over the eastern Pacific. && .HFO WATCHES/WARNINGS/ADVISORIES... Flood Watch through late Saturday night for Niihau-Kauai- High Surf Advisory until 6 PM HST Saturday for Niihau-Kauai Leeward-Waianae Coast-Kahoolawe-Maui Leeward West-Kona-Kauai South-East Honolulu-Honolulu Metro-Ewa Plain-Molokai Southeast- Molokai Leeward South-Lanai Leeward-Lanai South-Maui Central Valley South-South Maui/Upcountry-South Haleakala-Big Island South-Big Island Southeast. Small Craft Advisory until 6 AM HST Saturday for Big Island Windward Waters-Big Island Leeward Waters. && $$ DISCUSSION...Almanza AVIATION...Bohlin MARINE...Jelsema