Area Forecast Discussion
Issued by NWS Honolulu, HI
Issued by NWS Honolulu, HI
614 FXHW60 PHFO 202000 AFDHFO Area Forecast Discussion National Weather Service Honolulu HI 1000 AM 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 wind directions will be modified by local scale daytime sea breezes over sheltered areas of each island. Brief passing showers will favor mainly windward and mountain areas, particularly during the overnight through early morning hours. A disturbance will move through the islands from Tuesday night through Thursday morning, increasing windward and mauka showers midweek. && .DISCUSSION... High pressure is building back into the region today as the low pressure north of the state and a trough to the northwest continues to drifts slowly away from the main Hawaiian Islands. Latest satellite imagery this morning shows only a few clouds moving into windward and mountain areas with isolated to scattered showers. Most interior and leeward areas are experiencing mostly sunny to partly cloudy conditions this morning. A strong inversion was noted around 5,000 feet in the early morning Hilo sounding. With increasing stability and low inversion heights spreading westward, vertical cloud development and shower coverage will be rather limited today through Tuesday. Expect moderate to locally breezy east to east-southeast winds over the eastern half of the state and moderate winds over the western half through midweek. However, localized sea breezes will be possible during the daytime over sheltered areas. This will cause clouds to build over island interior sections today and Tuesday, though showers 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 just south of 30N by late Tuesday through Thursday. Meanwhile, a developing shortwave aloft will move into the eastern islands late Tuesday. This combination 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, easterly 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 is continuing to move away from the area and 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 later today and tonight. VFR conditions will prevail with brief MVFR conditions over windward slopes in passing clouds and showers. No AIRMETs are in effect and none are expected today. && .MARINE... A trough of low pressure far northwest of the state and a strong high far northeast of the state will produced fresh to strong trade winds over the eastern half of the state and moderate trades over the western half of the state 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 week. Surf along south-facing shores will remain at or near advisory heights through the day today. Recent south shore buoys observations show a swell of 3 to 4 feet with a periods of 16 to 17 seconds. The current south swell should gradually fade over the next few days and should drop below advisory thresholds by Tuesday. 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... High Surf Advisory until 6 PM HST this evening for all south facing shores. Small Craft Advisory until 6 AM HST Tuesday for Maui County Windward Waters-Maalaea Bay-Pailolo Channel-Alenuihaha Channel- Big Island Windward Waters-Big Island Leeward Waters-Big Island Southeast Waters. && $$ DISCUSSION...Vaughan AVIATION...M Ballard MARINE...Kino