Mostly dry and stable conditions with light to moderate trade winds will prevail today, with clouds and mainly light showers favoring windward and mauka locations through the early morning hours. A few cloud buildups and light showers are possible over leeward sections this afternoon where localized sea breezes form. A modest increase in moisture associated with a surface trough moving in from the east, combined with an upper-level disturbance, will support increasing rainfall chances from Tuesday into midweek. Trade winds will then strengthen into the breezy category Wednesday through the second half of the week as the trough and upper disturbance shift west of the area and the ridge strengthens north of the islands.
A relatively dry and stable trade wind pattern will persist today as a weak surface ridge remains positioned north of the islands. Light to moderate easterly trades will continue, with clouds and a few light showers primarily favoring windward and mauka areas through the morning hours. Afternoon heating and localized sea breeze development may support a few cloud buildups and brief showers over leeward and interior sections, but rainfall amounts should remain limited.
Conditions will begin to change late tonight into Tuesday as a surface trough moves in from the east and moisture begins to increase across the island chain. Guidance remains in good agreement showing precipitable water values rising to near 1.75 inches by Wednesday. At the same time, an upper-level shortwave trough is forecast to dig southward over the region, eventually cutting off and retrograding westward across the area through the middle part of the week. The approach of this upper disturbance will lower mid- and upper-level heights while helping to weaken and elevate the inversion. The combination of slightly deeper moisture, reduced stability, and enhanced large-scale lift associated with the upper low will support increasing shower coverage and rainfall potential from Tuesday through Thursday, particularly over windward and mauka areas, though some showers may periodically spread into leeward locations.
By late week into the weekend, both the surface trough and upper- level disturbance are expected to shift west of the state. In their wake, a strengthening subtropical ridge north of the islands will support a return to a more typical breezy trade wind pattern. Upper heights will gradually rise, the trade wind inversion will strengthen and lower, and precipitable water values are expected to decrease back toward climatological levels. As a result, shower activity should trend downward, with rainfall becoming focused over windward and mauka areas.
Vfr conditions will prevail with limited showers through tonight. Trade winds increase in strength over the next few days, decreasing the sea breeze coverage area. A passing strong low level trough will drift from east to west across the island chain, from Tuesday afternoon through Wednesday, increasing MVFR low level cloud cover and shower trends.
AIRMET Sierra in effect for mountain obscuration above 020 along the north and east slopes of the Big Island this morning. These low clouds will likely diminish later this morning.
A weak high pressure ridge will remain nearly stationary north of the waters maintaining gentle to locally fresh trade winds through Tuesday night. High pressure to the far north northeast will strengthen by midweek as easterly trade winds gradually strengthen to moderate to locally strong levels. A Small Craft Advisory (SCA) may need to be issued for the windier waters and channels around Maui County and the Big Island on Wednesday through the end of the week. A low level trough moving in from the east Tuesday through Wednesday will bring an increase in shower activity.
A series of small to moderate medium to long period south swells will keep surf along south facing shores elevated through the forecast period. Another boost in south swell is expected Wednesday night into Thursday below High Surf Advisory levels. Surf along east facing shores will remain small due to the lack of trade winds energy upstream of the islands through Tuesday. Easterly wind wave looks to increase Wednesday into the end of the week to moderate levels as trade winds increase. Surf along north facing shores will remain flat to tiny through the forecast period with potentially tiny background energy midweek into Thursday.
None.
