Area Forecast Discussion
Issued by NWS Honolulu, HI
Issued by NWS Honolulu, HI
327 FXHW60 PHFO 220119 AFDHFO Area Forecast Discussion National Weather Service Honolulu HI 319 PM HST Tue May 21 2024 .SYNOPSIS... Moderate to locally breezy trades will hold over the eastern islands, while lighter east southeast winds allow for some localized land and sea breezes over the western end of the state into Wednesday. Showers will favor windward and mauka areas overnight and during the morning hours, with a few showers developing over interior and leeward sections each afternoon and evening before clearing overnight and early morning. Moderate to breezy easterly trade wind pattern will overspread the state Wednesday night or Thursday and linger through early next week, with showers favoring windward and mauka areas and occasional leeward spillover. && .DISCUSSION... Currently at the surface, a trough of low pressure is located around 400 miles west-northwest of Kauai, while a 1035 mb high is centered around 1500 miles north-northeast of Honolulu. This light gradient will maintain moderate to locally breezy trade winds over the eastern islands, while light to moderate east southeast winds remain over the western end of the state into Wednesday. This pattern will allow localized leeward sea breezes increasing clouds and rain potential during the day and overnight land breezes clearing clouds and showers into the early morning hours for most sheltered areas over Kauai and Oahu. Visible satellite imagery shows upper and mid level cloud cover has thinned during the day today with low clouds focusing along windward and some leeward areas. An area of enhanced clouds is currently moving into Big Island windward areas. Radar imagery shows scattered clouds moving into windward areas of the Big Island and relatively dry conditions elsewhere across the state. Chances of rainfall will increase overnight for the rest of the state into Wednesday as this area of enhanced clouds and showers moves over the state from east to west. Moderate to breezy east southeast winds will transition to more easterly trades Wednesday into Thursday as the trough to the west- northwest of the state gradually shifts westward and the high to the northeast shifts north of the state. A series of reinforcing highs will build north of the state Friday through early next week. This will maintain moderate to breezy trade winds across the island chain through the forecast period. In addition drier air will filter in from the east allowing for a more stable trade wind pattern featuring mainly windward/mauka showers and the occasional leeward spillover. Showers will be mostly prevalent in the overnight and early morning hours. This pattern should hold through early next week. && .AVIATION... Moderate to breezy east to southeast winds will persist through tomorrow. A few leeward showers are possible this afternoon where localized sea breezes form. A plume of moisture moving towards the eastern end of the state this afternoon will bring an uptick in showers and cloud cover to mainly windward Big Island and Maui by this evening...which could lead to periodic MVFR conditions. To a lesser extent, windward clouds and showers may increase slightly across the rest of the island chain tonight into tomorrow morning. Otherwise, VFR conditions will prevail. AIRMET Sierra is in effect for mountain obscuration over the windward slopes of the Big Island and Maui this afternoon and is expected to be needed overnight for these areas as well. && .MARINE... Strong high pressure centered nearly 1300 nm northeast of the state is driving fresh to strong easterly trade winds around the Big Island and Maui, and a surface trough sitting roughly 250 nm northwest of Kauai is causing winds to shift out of the east- southeast and ease slightly around Oahu and Kauai. A Small Craft Advisory (SCA) is currently in place for all waters around the Big Island, waters north of Maui, and the Pailolo Channel. As the trough weakens and drifts westward, expect the stronger easterly trades winds to spread to Oahu and Kauai on Wednesday, with the SCA likely adjusted to cover the typically windy waters around the Big Island and Maui County. Moderate to strong easterly trade winds will persist into the weekend. The current south swell is on a gradual decline, but recent PacIOOS buoy measurements show it near 3 feet at 13 to 14 seconds. Expect a slow downward trend over south and exposed west shores through Wednesday, with only small inconsistent pulses of southwest swell for the remainder of the week. Rough surf along east facing shores will slowly rise over the next few days as the trades strengthen upstream of the state. Surf along north shores will remain small with a slight bump possible around Sunday or Monday. && .HFO WATCHES/WARNINGS/ADVISORIES... Small Craft Advisory until 6 AM HST Thursday for Maui County Windward Waters-Pailolo Channel-Alenuihaha Channel-Big Island Windward Waters-Big Island Leeward Waters-Big Island Southeast Waters. && $$ DISCUSSION...Almanza AVIATION...Farris MARINE...Wroe