Area Forecast Discussion
Issued by NWS Honolulu, HI
Issued by NWS Honolulu, HI
504 FXHW60 PHFO 210147 AFDHFO Area Forecast Discussion National Weather Service Honolulu HI 347 PM HST Mon May 20 2024 .SYNOPSIS... The low pressure system far north of the state will continue to drift slowly northward over the next few days as high pressure builds back into the region. Expect moderate to locally breezy east to east-southeast winds over most islands through midweek, though daytime sea breezes will occur over sheltered areas of each island. Brief passing showers will favor mainly windward and mountain areas. A disturbance will move through the islands from Tuesday night through Thursday morning, increasing windward and mauka showers. && .DISCUSSION... Locally breezy east-southeast flow is prevailing over the eastern end of the state today, with more moderate winds farther west as the low pressure system far north of the islands gradually lifts northward. Within this east-southeast flow regime, showers and clouds have been common today across windward and southeastern sections of the Big Island. Additionally, daytime sea breezes over areas sheltered by island terrain have increased clouds over select inland and leeward locations as well, but afternoon soundings at Hilo and Lihue reveal a strongly capped environment which has limited overall shower potential. Expect moderate to locally breezy east to east-southeast winds over the eastern half of the state and moderate winds over the western half into Tuesday. Localized sea breezes will be possible during the daytime over sheltered areas again Tuesday. This will again cause clouds to build over island interior sections though overall shower activity will remain limited. Low pressure aloft associated with the kona low to the north of the state will swing around and develop into a new trough and eventual low in the mid- to upper levels. A weak surface low is forecast to develop along a trough just south of 30N by Thursday. Meanwhile, a developing shortwave aloft will move into the eastern islands late Tuesday. This could increase moisture depth and result in and increase in windward and mauka showers spreading across the island chain from west to east from Tuesday night through Thursday morning, particularly during the overnight through early morning hours. From Thursday through the rest of the week, trade winds spread to all islands. Broad upper level troughing will keep passing showers mainly during the overnight to early morning hours favoring windward and mountain areas. && .AVIATION... A surface trough to the west and continuing to move away from the area will allow a surface trough north of the islands to strengthen. This will allow light to moderate east to southeast winds to transition to moderate trade winds tomorrow. While VFR conditions continue to prevail over the smaller islands, clouds and showers that have developed over the Big Island have led to the issuance of AIRMET Sierra for mountain obscuration. Expect conditions to improve after sunset. No additional AIRMETS are expected into tonight. && .MARINE... A trough of low pressure just west and northwest of the state will continue to linger through the first half of the week. Meanwhile, a strong high will remain nearly stationary far northeast of the state through most of the week. The combination of the trough to our west and the high to the northeast will produce locally strong trades over the eastern half of the state and moderate trades over the western half through Tuesday. A Small Craft Advisory is in effect for the windier zones around Maui County and the Big Island. Starting late Tuesday night into Wednesday, another trough will develop west of the state and will cause the winds to weaken and veer toward the southeast over the western half of the state. By Thursday, the trough should weaken and we should see fresh to locally strong trades across the state through the rest of the work week. Trades may weaken a touch over the weekend as the high far northeast of the state weakens. Surf along south-facing shores will continue to gradually decline over the next several days. Near-shore buoys did show a decline below high surf advisory thresholds, thus the High Surf Advisory has been cancelled. Surf heights should continue to remain above the summer average (5 feet) through Tuesday then dissipated around Wednesday. A gale force low currently in the South Pacific near 36S120W showed winds near storm force directed toward the state on the OSCAT pass yesterday. This does increase the potential for a small southeast swell Friday into the weekend. Surf along east facing shores should see a gradual rise over the next several days as the trades strengthen upstream of the state. && .HFO WATCHES/WARNINGS/ADVISORIES... Small Craft Advisory until 7 AM HST Wednesday for Pailolo Channel-Alenuihaha Channel-Big Island Leeward Waters-Big Island Southeast Waters. && $$ DISCUSSION...Vaughan AVIATION...M Ballard MARINE...Kino