Area Forecast Discussion
Issued by NWS Honolulu, HI
Issued by NWS Honolulu, HI
273 FXHW60 PHFO 190120 AFDHFO Area Forecast Discussion National Weather Service Honolulu HI 320 PM HST Sat May 18 2024 .SYNOPSIS... Heavy showers and isolated thunderstorms will remain possible over Oahu through this evening, while ample moisture over Kauai County will continue the threat for heavy rain there through tonight. 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... Latest radar and satellite imagery shows heavy showers and isolated thunderstorms moving over the island of Oahu this afternoon, with lighter rain observed over Kauai. This moisture is being drawn northward by a kona low that is located northwest of the main Hawaiian Islands with a trough located near Kauai. Additionally, surface convergence from more easterly flow across the central islands and southerly flow wrapping around the southern tip of the Big Island has sparked convection within an unstable environment over the western portion of the state. This is resulting in the occasional heavy showers and isolated thunder observed over Oahu today. Some of the hi-res guidance has been hinting at this possibility over the past day or so as we transition from the southerly flow back to easterly flow. A Flood Watch remains in effect for Kauai County through tonight as pockets of heavy rain will remain possible. Additionally, convergence upstream of Oahu could continue to produce occasionally heavy showers moving into Oahu into the evening, but should trend down during the overnight hours. High pressure will build in from east to west across the state Sunday as the kona low shifts north and weakens. Expect more stabilizing trends with decreasing showers as east to southeast winds spread across the state on Sunday. By Sunday, the moderate to heavy rainfall threat will diminish as more stable conditions fill in across the state. 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 a 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 just west of Kauai will maintain an unstable environment, especially over the western half of the state. Heavy showers developed over Oahu earlier today and will continue to impact Oahu with periods IFR conditions possible in moderate to locally heavy showers through this evening. Over on Kauai, steady periods of light to moderate rain is expected to continue through this evening with a decrease of rain expected late tonight. Periods of MVFR conditions will be possible with the heavier showers on Kauai. A deep upper level trough will continue to produce light to moderate turbulence across the state from FL280-400 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 especially this afternoon through tonight. AIRMET ZULU is in effect. && .MARINE... Locally strong E to SE winds will persist through the weekend before transitioning to easterly early next week. A Small Craft Advisory remains in effect through Sunday for the windier waters around Maui County and the Big Island. Surf along S facing shores will remain elevated through early next week due to overlapping long-period SSW swells. The first swell has peaked and the period is gradually shortening. However, ample energy is still found in the 15-16 second band. In addition, the second SSW swell will fill in during Sunday, peaking early next week slightly lower than the present swell. The High Surf Advisory has been extended through Sunday. 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. && .HFO WATCHES/WARNINGS/ADVISORIES... Flood Watch through late tonight for Niihau and Kauai. High Surf Advisory until 6 PM HST Sunday for south facing shores of all islands. Small Craft Advisory until 6 PM HST Sunday for Maui County Windward Waters-Alenuihaha Channel-Big Island Windward Waters- Big Island Leeward Waters. && $$ DISCUSSION...Vaughan AVIATION...Kino MARINE...JVC