Drought in Hawaii, September 1 to 30, 2021

Area Forecast Discussion
National Weather Service Honolulu HI
823 PM HST Tue Aug 31 2021

.SYNOPSIS...
Light winds and humid conditions will continue into Wednesday,
with clouds and showers favoring interior and leeward areas
through the afternoon hours. Breezy trade wind conditions will
return Wednesday night through the second half of the week,
shifting clouds and showers back to the typical windward and mauka
locations. Trades may ease late in the weekend and into early
next week as another trough moves into the area.

&&

.DISCUSSION...
The land and sea breeze regime with a light east to southeast
background flow in place will continue into Wednesday as an upper
low and surface trough continue westward and away from the
region. This combined with a slug of moisture clipping the
islands from east to west will support humid conditions
continuing, along with another round of afternoon showers
Wednesday where sea breezes develop. Recent satellite-derived
precipitable water (PW) data reflected this area of higher
moisture (2" PWs) lurking south of the Big Island this evening.

Near-term guidance remains consistent and depicts a drying trend
through the second half of the week as upper heights rise and
the surface ridge builds to the north. Breezy trades combined with
lowering dewpoints will be the result. Clouds and showers will
shift back to the typical windward and mauka locations, with the
best coverage overnight though the morning periods as pockets of
moisture move through.

The long-term guidance depicts the pressure gradient loosening
once again late in the weekend and into early next week as an
upper low moves in and a weakness forms in the subtropical ridge
to the north. If this materializes, trades will become disrupted
with another land and sea breeze pattern setting up.

&&

.AVIATION...
Trade winds will return later tomorrow with localized sea breezes
lingering along western terrain sheltered slopes. Convergence
boundaries between the trade winds and daytime sea breezes will
produce day time showers over leeward areas. Otherwise the
returning trade wind regime will shift cloud and shower activity
back to windward and mountain areas favoring the overnight to
early morning hours. Brief MVFR is possible with shower activity.

No AIRMETs in effect and none are expected.

&&

.MARINE...
The weak trough near the islands that has recently disrupted
trade flow and introduced several days of light winds will be
moving west of the area through Wednesday. This will allow high
pressure centered far northeast of the state to assert more of an
influence through late week. The tighter pressure gradient
produced from this high will reawaken more areawide moderate to
locally strong trade winds from Wednesday evening into the Labor
Day Weekend. Trades will likely be strong enough over the
typically windier areas surrounding Maui County and south of Big
Island Thursday to warrant a Small Craft Advisory (SCA). Trades
are expected to further strengthen on Friday which could support
expanding the SCA to most, if not all, of the local coastal
waters.

No significant swells are expected through the weekend. A series
of small, long period south and southeast swells will maintain
seasonal south facing shore surf through the remainder of the
week. Strengthened trades over and upstream of the chain will
bring in a higher wind wave swell. This will build east facing
shore surf to near normal levels from Thursday through the
weekend.

&&

.HFO WATCHES/WARNINGS/ADVISORIES...
None.

&&

DISCUSSION...Gibbs
AVIATION...Bohlin
MARINE...Blood