Drought in Hawaii, September 8 to 30, 2020

Area Forecast Discussion
National Weather Service Honolulu HI
821 PM HST Mon Sep 7 2020

.SYNOPSIS...
A ridge of high pressure north of the state will keep light to
moderate trades in place through Tuesday night. A band of low
clouds and showers will bring a modest increase in rainfall
coverage to windward areas tonight and again Tuesday night, with
a few showers possibly reaching the parched leeward sections of
the islands. The trades should increase into the moderate to
locally breezy range Wednesday and Thursday, with a drier airmass
bringing a decrease in shower activity statewide during this time.
This drier airmass should persist through Friday, with the trades
easing back to moderate levels. The trades should ease further
over the weekend into early next week, with showers becoming a
bit more common in windward areas, and a few showers developing
each afternoon and early evening hours over leeward and interior
locales.

&&

.DISCUSSION...
Currently at the surface, a stationary front is located around 700
miles northwest of Kauai, with a weak trough of low pressure located
around 1000 miles northeast of Hilo. Meanwhile, a strong 1035 mb
high is centered around 2250 miles north-northeast of Honolulu
with ridging extending southwestward, between the previously
mentioned front and trough, to a location several hundred miles
northwest of Kauai. The resulting gradient is producing light to
moderate trade winds across the island chain this evening.
Infrared satellite imagery shows a band of low clouds moving into
windward areas, resulting in mostly cloudy conditions in most
locales, with partly cloudy skies in place in most leeward areas.
Radar imagery shows scattered to numerous showers moving into
windward areas, with a few of these showers reaching leeward
locales from time to time. Main focus the next few days revolves
around trade wind trends and rain chances.

The ridge of high pressure north of the islands will change very
little during the next 24 to 36 hours, keeping a generally light
to moderate trade wind flow in place, strongest during the
daylight hours. We should see the trades increase a notch
during the middle of the week as the ridge north of the islands
strengthens slightly and a weak trough of low pressure slides by
to the south of the state. This should be enough to boost trades
into the moderate to locally breezy range Wednesday through
Thursday. The ridge north of the islands appears to weaken and
shift closer to the islands Friday through early next week. This
should ease the trades to moderate levels by Friday, and into the
light to locally moderate range over the weekend into early next
week, with afternoon sea breezes possible in the more sheltered
leeward areas.

As for the rest of the forecast, the band of low clouds and
showers moving into windward areas, will keep showers a bit more
active tonight into Tuesday morning. Showers will favor windward
and mauka areas with a few showers reaching leeward areas at
times. We should see a similar increase in trade showers Tuesday
night into Wednesday morning, before a slightly drier airmass
moves in by Wednesday afternoon. This drier trade wind pattern
should then prevail through Friday, with scattered showers
affecting mainly affecting windward areas during the overnight
and early morning hours. A slight increase shower activity is
expected Friday night through early next week, as the airmass
moistens up a bit and a weak trough aloft moves over the state.
This should increase shower coverage over windward locales, and
allow for the development of a few afternoon/early evening showers
in leeward and interior areas.

&&

.AVIATION...
Light to moderate east northeast trades will persist across the
islands tonight with various pushes of low level clouds and
showers. Scattered shower activity will mainly affect windward
coasts and slopes, while isolated activity is expected elsewhere.
Brief periods of MVFR ceilings and visibility may accompany these
showers.

No AIRMETs are currently in effect.

&&

.MARINE...
A surface ridge far north of the state will maintain moderate to
fresh trades through most of the week. The trade winds may
briefly approach the Small Craft Advisory criteria across some of
the typically windier waters adjacent to the islands of Maui
County and the Big Island through mid-week. As we approach next
weekend, the surface ridge is expected to weaken and shift
southeast as a front passes far north of the area. This will
likely cause the pressure gradient to relax across the region,
which is expected to produce weaker trade winds by the weekend.

The current south-southwest swell will be trending down over the
next few days, with a small reinforcing south-southwest swell
expected during the second half of the week. In addition, small
southeast swell energy is expected to maintain small surf along
exposed shorelines through the weekend. Surf along most north and
west facing shores of the smaller islands is expected to increase
starting Tuesday due to the arrival of a small northwest swell.
The surf produced by this swell is expected to peak Wednesday,
then gradually subside from Thursday through Friday. Surf along
east facing shores is forecast to gradually subside later this
week as the trades weaken locally and upstream of the state.

&&

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

&&

DISCUSSION...Jelsema
AVIATION...Thomas
MARINE...Houston