Area Forecast Discussion
Issued by NWS Honolulu, HI
Issued by NWS Honolulu, HI
876 FXHW60 PHFO 120122 AFDHFO Area Forecast Discussion National Weather Service Honolulu HI 322 PM HST Sat May 11 2024 .SYNOPSIS... A land and sea breeze pattern will bring afternoon clouds and showers to island interiors into the middle of next week. Another low will bring the threat of heavy rain to the islands during the second half of the week. && .DISCUSSION... Interior showers and isolated thunderstorms over the islands will dissipate with the loss of diurnal heating this evening. Steep 700-500mb lapse rates with provide a significant boost to any convection that overcomes lower level stability, especially over upslope portions of the Big Island. With heavy rain continuing at press time, the Flood Watch remains in effect. It is expected to expire on schedule at 8pm HST this evening. The resident upper low will slowly reabsorb into the mid- latitude westerlies during the next few days leaving the islands firmly within the trailing envelope of cyclonic flow aloft, though forcing and instability will diminish. In the near term (Sunday into Monday), the established airmass will remain in place with continued weak troughing over the islands supporting a light easterly gradient and the consequent land and sea breeze pattern. This will favor afternoon cloud build ups and interior showers of lesser intensity than recent days. Strong consensus exists among the global models that high amplitude mid-latitude troughing will beget another closed low in the vicinity of the islands during the middle of next week. The local gradient responds to the associated height falls as early as Monday-Tuesday when surface winds veer to southeasterly and advect higher dewpoints (near 70F) into the region. In addition to the lack of meaningful wind and increasingly uncomfortable humidity, this will supply plenty of boundary layer moisture for afternoon showers as the sea breeze pattern continues. The second half of next week bears watching as the aforementioned closed low reaches its southernmost extent. Current consensus indicates PWATs rising toward 2" as convergent southwesterly flow establishes over the islands leading to an elevated heavy rain threat. The inherited forecast handles this potential well, including the risk of thunderstorms. && .AVIATION... A strong upper level disturbance will continue to gradually move across the state through the weekend. As a result, enhanced shower activity and isolated thunderstorms will continue to produce periods of MVFR and local IFR conditions. Light to moderate winds have allowed for some sea breeze development this afternoon...which has led to the building clouds and showers over interior and sheltered leeward areas. With both the upper level disturbance and light to moderate surface winds persisting across the area through the weekend, a similar yet less intense pattern can be expected tomorrow. AIRMET Sierra for tempo mountain obscuration is in effect across the entire island chain this afternoon. This AIRMET will likely be needed on and off throughout the evening into tomorrow for portions of island chain as showers develop and dissipate. AIRMET Tango for moderate to isolated severe mid to upper level turbulence remains in effect as the upper level disturbance moves across the state. Conditions will likely improve by tomorrow morning. AMD NOT SKED for PMDY continues due to equipment issues, with no timeline for restoration. AMD NOT SKED for PHJR also due to equipment issues. && .MARINE... A few thunderstorms will remain possible across mainly across windward waters for the eastern half of the state tonight as an upper disturbance continues to linger nearby. Light and variable winds are prevailing across the area, except within and near thunderstorms. Light to moderate easterly trade winds will begin building back into the region on Sunday. Winds will weaken again and become more southerly by Monday night as high pressure becomes established both far northeast and far northwest of the islands and high amplitude troughing ensues in between these features. Surf along south facing shores remains elevated, but will slowly decline through Sunday and then hold into early next week as a long-lived, small south swell continues to affect the islands. Although the swell size itself will remain largely unchanged through Sunday night, the period will gradually shorten, allowing surf heights to slowly trend down. Another series of overlapping, long-period south swells will begin moving in on Tuesday, with reinforcements giving another noticeable boost to south shore surf from Wednesday through the rest of next week. A small, short-period north-northwest swell will decline tonight today into Sunday. A reinforcing small, long-period northwest swell will build Sunday night, giving north shore surf a boost early next week. Surf along east facing shores will be well below normal levels through the middle of next week. && .HFO WATCHES/WARNINGS/ADVISORIES... Flood Watch until 8 PM HST this evening for Niihau-Kauai Leeward- Kauai Mountains-Waianae Coast-Oahu North Shore-Olomana-Central Oahu-Waianae Mountains-Lanai Mauka-Kahoolawe-Maui Windward West- Maui Leeward West-Haleakala Summit-Kona-Kohala-Big Island Interior-Kauai North-Kauai East-Kauai South-East Honolulu- Honolulu Metro-Ewa Plain-Koolau Windward-Koolau Leeward-Molokai- Lanai Windward-Lanai Leeward-Lanai South-Maui Central Valley North-Maui Central Valley South-Windward Haleakala-Kipahulu- South Maui/Upcountry-South Haleakala-Big Island South-Big Island Southeast-Big Island East-Big Island North. Wind Advisory until 6 AM HST Sunday for Big Island Summits. && $$ DISCUSSION...JVC AVIATION...Farris MARINE...Vaughan