Area Forecast Discussion
Issued by NWS Honolulu, HI
Issued by NWS Honolulu, HI
982 FXHW60 PHFO 190655 AFDHFO Area Forecast Discussion National Weather Service Honolulu HI 855 PM HST Sat May 18 2024 .SYNOPSIS... Heavy showers and isolated thunderstorms will remain possible over Oahu and Kauai through this evening. Expect improving trends from east to west on Sunday. By Monday all islands will see an improvement in weather conditions as easterly trade winds return. && .DISCUSSION... A heavy rainfall and thunderstorm threat remains for Kauai and Oahu through tonight. A Flood Watch remains in effect for Kauai through early morning Sunday. Latest satellite and radar shows and area of isolated thunderstorm activity and enhanced showers located 80 miles west of Kauai County that is steadily moving east. This area will likely move over Kauai late tonight through early morning Sunday, producing moderate to locally heavy rainfall. The area may even reach portions of Oahu. Any excessive rainfall that may develop over Oahu overnight could very easily require a Flood Advisory given the saturated environment from these past couple of days. Over the rest of the state, composite radar loop shows that light showers are fairly widespread west of the Big Island with scattered moderate showers embedded moving from the southwest to the northeast. High pressure will build in from east to west across the state Sunday as the kona low shifts north and weakens. Breezy east to southeast winds will become more light and variable over the smaller island due to Big Island shadowing the smaller islands Sunday. The axis of above normal moisture is expected to shift northwest along with the associated moderate to heavy rainfall threat. An upper level short wave trough will exit to the east. Expect more stabilizing trends over the western half of the state. A slight chance of thunderstorms has been added to the Big Island afternoon forecast as this area of upper level instability shifts east. Easterly trade winds will return across the islands from Monday onward. Trade wind showers may be somewhat enhanced during the first half of next week due to lingering moisture and some upper level instability from another short wave trough. Precipitable water values will return to normal during the second half of the week, supporting a more typical trade wind pattern. && .AVIATION... A trough west of Kauai will allow frequent showers to persist through tonight, mainly for areas west of Maui. In addition, enough instability still exists to maintain a slight chance of thunderstorms for Kauai, Oahu, and surrounding waters. Heavier pockets of rain will likely bring periods of MVFR ceilings/visibility with isolated pockets of IFR ceilings and visibility. Conditions should improve through the day on Sunday. Expect a slight chance of diurnally driven afternoon thunderstorms over the Big Island on Sunday. A deep upper level trough will continue to bring areas of moderate turbulence across the state from FL250-400 through Sunday. AIRMET Tango is in effect across the state due to the upper level turbulence. AIRMET Sierra in effect for mountain obscurations over most islands except Big Island. Periods of light to moderate rime icing is expected from Kauai to Oahu in layer 130-FL220 through tonight. AIRMET ZULU is in effect. && .MARINE... Locally strong east-southeast winds will persist through Monday, before transitioning to easterly trades Tuesday through late next week. A Small Craft Advisory remains in effect through Sunday for the windier waters around Maui County and the Big Island. The current south swell will slowly lower tonight and Sunday, while a new long-period south swell fills in. This will keep south shore surf near low end advisory levels through Sunday. The swell will hold Sunday night and Monday, then gradually lower through the middle of next week. South shore surf will fall back below the summertime average Thursday through next weekend, with only small south and south-southwest swells rolling through. The current small northwest swell will gradually lower tonight through Monday, with north shore surf going flat Tuesday through next weekend. Surf along east facing shores will remain well below average through early next week. An upward trend is expected Tuesday through late next week as trade winds strengthen over and upstream of the islands. && .HFO WATCHES/WARNINGS/ADVISORIES... Flood Watch until 6 AM HST Sunday for Niihau-Kauai- High Surf Advisory until 6 PM HST Sunday for all south facing shores. Small Craft Advisory until 6 PM HST Sunday for Maui County Windward Waters-Alenuihaha Channel-Big Island Windward Waters- Big Island Leeward Waters. && $$ DISCUSSION...Almanza AVIATION...Thomas MARINE...Jelsema