Area Forecast Discussion
Issued by NWS Honolulu, HI
Issued by NWS Honolulu, HI
047 FXHW60 PHFO 201348 AFDHFO Area Forecast Discussion National Weather Service Honolulu HI 348 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. The high pressure ridge will build in north of the state as the low drifts away from the island chain. Expect moderate to locally breezy east to east- southeast winds over most islands through Wednesday, wind directions will be modified by local scale daytime sea breezes over terrain sheltered areas of each island. Brief passing showers will mainly drift over windward and mountain areas in the evening through early morning hours. A low level disturbance will move westward through the islands from Tuesday night through Thursday morning enhancing shower activity from east to west across the state. && .DISCUSSION... Satellite imagery this morning shows a band of middle and high clouds drifting east of the Big Island. Upper air balloon soundings from 2 AM HST at Lihue and Hilo show subsidence temperature inversion heights around 5,000 feet above sea level. At these low inversion heights the air mass remains fairly stable and tends to cap vertical cloud development due to strong subsidence. Decreasing clouds and showers will likely continue into Tuesday afternoon for most islands. The low pressure system far north of the state will continue to drift slowly northward over the next few days. The high pressure ridge will build in north of the state as the low drifts away from the island chain. Expect moderate to locally breezy east to east- southeast winds over most islands through Wednesday, wind directions will be modified by local scale daytime sea breezes over terrain sheltered areas of each island. Clouds will build over island interior sections with limited shower activity for most islands through Tuesday. Tuesday night into Thursday morning...A low level easterly wave, shown on satellite imagery east of the Big Island around 148W longitude and the GFS 700 MB streamlines, will move into the eastern islands of Maui and the Big Island late Tuesday. This trough will increase inversion heights and allow deeper clouds and higher shower trends to develop over the eastern slopes of both islands. By Wednesday this trough moves into the central islands spreading increasing cloud and shower trends to windward and mountain areas statewide. By Thursday morning easterly trade winds spread to all islands and the instability from this low level trough enhances trade wind showers over the windward and mountain slopes of the western islands. Thursday afternoon through Sunday...Moderate to locally breezy trade winds remain in the forecast with broad upper level troughing will keep passing showers mainly during the overnight to early morning hours favoring windward and mountain areas. && .AVIATION... Light to moderate east to southeast winds will persist through the 24-Hr forecast period. Brief periods with MVFR CIGs/VSBYs in showers are possible over windward areas this morning, then over leeward and interior locations this afternoon where sea breezes form. && .MARINE... Maritime moderate easterlies with localized fresh to strong winds through eastern island bays, channels and south of Big Island will be the general wind regime through the week. The Small Craft Advisory (SCA) for the notoriously windier waters surrounding Maui County and Big Island has been extended through early Tuesday morning and expanded to include Maalaea Bay and Pailolo Channel. Surf along south-facing shores will remain at or near advisory heights through early afternoon. Recent south shore buoy observations of around 3 to 4 feet, near 16-18 second swell, along with spectral density plots showing additional long period energy reaching southern shores this morning, will maintain High Surf Advisory (HSA) level surf through the early afternoon hours. While south energy will be fading through the day, the HSA has been extended through the afternoon to account for the passage of the tail end of this energy. As the south swell fades, south shore surf is forecast to wane from tonight through the middle of the week. The weekend`s small northwest swell will subside through the day with resultant north shore surf falling to near flat from Tuesday into the weekend. East chop will remain steady through early week. There may be a slight mid to late week uptick in wind wave action as trades strengthen a bit over and upstream of the islands. && .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...Bohlin AVIATION...Gibbs MARINE...Blood