Area Forecast Discussion
Issued by NWS Honolulu, HI
Issued by NWS Honolulu, HI
614 FXHW60 PHFO 200657 AFDHFO Area Forecast Discussion National Weather Service Honolulu HI 857 PM HST Sun May 19 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. && .DISCUSSION... Satellite imagery this evening shows a band of middle and high clouds drifting over the eastern end of the Hawaiian Islands. Upper air balloon soundings from 2 PM HST at Lihue and Hilo show subsidence temperature inversion heights in the 5,000 to 6,000 foot elevation range. These low temperature inversion heights indicates a stable air mass with strong subsidence across the state and are expected to continue into Tuesday for most islands. Tuesday through Wednesday...A low level easterly wave, shown on satellite imagery east of the Big Island around 147W 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. Thursday through Saturday...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 and beyond. Although VFR conditions will prevail, brief periods with MVFR CIGs/VSBYs in showers moving through are possible over windward areas overnight into Monday morning. Afternoon showers are also possible over leeward areas where localized sea breezes form. AIRMET TANGO remains in effect for moderate upper level turbulence from FL250-350, which will likely continue into Monday. AIRMET Zulu is in effect for areas of light to moderate rime icing in the layered clouds from Maui to the Big Island. Conditions should gradually improve from west to east overnight as the mid to high clouds drift eastward. && .MARINE... Maritime moderate easterlies, with localized fresh to strong winds through eastern island bays, channels and south of Big Island, will persist through the week. A Small Craft Advisory (SCA) is currently in effect through Monday afternoon for the notoriously windier waters surrounding Maui County and Big Island. Winds through Maalaea Bay and Pailolo Channel may reach SCA thresholds by Monday night. Therefore, the SCA may need to be expanded in areal coverage to include these zones. Surf along south-facing shores will remain at or near advisory heights tonight. Evening south shore buoy observations of 3 to 4 foot, near 16 second swell, with spectral density plots showing additional long period energy reaching southern shores this evening, will likely maintain High Surf Advisory (HSA) surf into the early Monday morning hours. This warrants a continuance of the HSA for south-facing shores through Monday sunrise. The HSA may need to be extended through the morning but will be likely be dropped by Monday afternoon. As the south swell fades, south shore surf is forecast to wane from Monday through the middle of the week. The current very small northwest swell will gradually ease through Monday with resultant north shore surf conditions falling to near flat from Tuesday on through next weekend. East chop will remain steady through early week. There may be a slight mid to late week uptick in wind waves as trades strengthen a bit upstream of the islands. && .HFO WATCHES/WARNINGS/ADVISORIES... High Surf Advisory until 6 AM HST Monday for south facing shores of all islands. Small Craft Advisory until 6 PM HST Monday for Maui County Windward Waters-Alenuihaha Channel-Big Island Windward Waters- Big Island Leeward Waters-Big Island Southeast Waters. Wind Advisory until 6 AM HST Monday for Big Island Summits. && $$ DISCUSSION...Bohlin AVIATION...Gibbs MARINE...Blood