Area Forecast Discussion
Issued by NWS Honolulu, HI
Issued by NWS Honolulu, HI
469 FXHW60 PHFO 260659 AFDHFO Area Forecast Discussion National Weather Service Honolulu HI 859 PM HST Tue Jun 25 2024 .SYNOPSIS... A stable trade wind pattern will persist through much of the week with breezy to locally windy trades. Periodic light showers will focus over windward and mauka areas during this time. An increase in shower activity and isolated thunderstorms will be possible over portions of the state from Friday into the weekend as an upper-level disturbance approaches and moves over the region. && .DISCUSSION... This afternoon, surface high pressure remains centered far north of the main Hawaiian Islands. The 00z sounding from Hilo continues to show a strong inversion around 4500 feet with little moisture trapped below the inversion. This is supported by regional satellite imagery, which shows only a few clouds over windward areas of Maui County and the Big Island. Meanwhile, the western end of the state has experienced a few more showers and windward clouds today as the band of moisture that was near Kauai this morning has continued to move through (although it is dissipating this afternoon). High pressure to the north is expected to weaken slightly over the next couple of days. This should relax our local pressure gradient a bit, but winds will still remain breezy through much of the week. Impulses of moisture embedded in the trade wind flow will continue to favor windward and mauka areas, though rainfall accumulation will be limited. Aside from some brief afternoon/evening showers over Kona slopes of the Big Island, leeward areas will remain mostly dry. Conditions start to change near the end of this week and into the weekend as guidance continues to show a disturbance aloft moving across the islands from east to west. Looking back at the past several model runs, they have been very consistent in bringing a low aloft near the islands on Friday, and then have it passing over the islands from the east this weekend. This feature will increase instability as it moves near the western end of the state. This instability could enhance trade wind showers, particularly on Saturday night. Isolated thunderstorms are also a possibility, both over the western end of the island chain closer to the upper low and over the slopes of the Big Island Friday and Saturday afternoons. With this afternoon`s forecast updates, thunderstorms have been added for these areas given the increasing confidence. With that said, precipitable water values may be a limiting factor, preventing showers and thunderstorms from reaching their full potential. Therefore, expect further refinements to the forecast for the Friday through Sunday period as details become more clear this week. && .AVIATION... Breezy trade winds will persist across the island chain through the next 24 to 48 hours. Showers and low clouds riding in on these trades will bring brief periods of MVFR conditions over windward and mauka locations. Otherwise, VFR conditions will prevail. AIRMET Tango remains in effect for moderate low-level turbulence over and downwind of island terrain due to breezy trade winds under the tradewind inversion. AIRMET Sierra for tempo mountain obscuration across windward Kauai will be cancelled but may be needed again later if shower coverage increases. && .MARINE... High pressure will remain present over the Central North Pacific through the weekend and possibly into next week. Moderate to locally strong easterly trades will persist through Thursday. The high will weaken slightly toward the end of the week into the weekend easing trades to gentle to fresh range. The Small Craft Advisory (SCA) for the typically windier waters around Maui County and the Big Island has been expanded through Thursday afternoon. An upper level low may bring isolated thunderstorms which could imply locally higher winds and seas. Surf along east-facing shores will gradually ease through the week as the winds locally and upstream trends down through the week. A small, medium-period, south swell has peaked and will trend down into Wednesday. Another small, medium- to long- period south swell will fill in Wednesday night, peak Thursday night before gradually easing into the weekend. Surf along north facing shores will be minimal through tonight into Wednesday. A small, medium period, northwest swell could fill in late Wednesday, peaking Thursday night providing a small bump along north facing shores through the rest of the week. && .HFO WATCHES/WARNINGS/ADVISORIES... Small Craft Advisory until 6 PM HST Thursday for Maalaea Bay- Pailolo Channel-Alenuihaha Channel-Big Island Leeward Waters-Big Island Southeast Waters. && $$ DISCUSSION...Thomas AVIATION...Shigesato/Powell MARINE...Almanza