697
FXHW60 PHFO 081951
AFDHFO

Area Forecast Discussion
National Weather Service Honolulu HI
951 AM HST Sun Sep 8 2024

.SYNOPSIS...
Light to moderate trade winds will bring a few brief showers,
mainly to windward areas this morning, before gradually diminishing
through tonight. Light and variable winds thereafter will result
in mostly clear nights and mornings, and warm and muggy afternoons
and evenings with minimal rainfall through Wednesday. Trade winds
will return by Thursday, and remain breezy into next weekend.

&&

.DISCUSSION...
Two areas of high pressure, one to the far NE of the islands and
one to the far NW, will continue to support light to moderate
trade wind flow through this afternoon. The upper air sounding at
Hilo earlier this morning showed a strong temperature inversion
around 5700 feet with substantial dry and warm air aloft. Current
satellite and radar imagery shows only scattered low clouds with
isolated light showers across the islands, indicative of the
stable conditions aloft.

A strong shortwave trough aloft to the far NNE of the islands is
digging sharply southward along 152W today. This feature is expected
to develop into a strong cutoff low as it stalls about 900 miles
NNE of the state. As this low moves slowly west and eventually SW
tonight through Tuesday night, the local pressure gradient will
become quite weak, resulting in light and variable winds over the
islands. As the low slowly dissipates and begins to move N later
in the week, high pressure building in to replace it will promote
a light SE flow on Wednesday, followed by strengthening easterly
trade wind flow by Thursday.

Rainfall-wise, a strong mid-level ridge will provide anomalously
warm 500 mb temperatures and a relatively dry environment (with
near to below normal precipitable water values). Therefore, the
airmass over the islands is expected to be quite stable and any
rainfall that does occur during the first half of this week will
be minimal. As winds become light and variable over the next couple
of days, overnight land breezes and daytime sea breezes will develop.
This will result in mostly clear nights and mornings with warm, muggy
afternoons and chances for interior and mauka clouds and isolated
light showers. The one caveat to this forecast is that models do
show a dissipating frontal boundary nearing Kauai around Tuesday.
This could result in a few more clouds and slightly better shower
coverage for the Garden Isle than the rest of the state. A more
typical trade wind shower regime will return for the latter portion
of the week.

&&

.AVIATION...
Trade winds will weaken to light and variable by tonight and continue
for the next several days. Afternoon low clouds with isolated showers
expected across most islands as onshore flow begins to take over
for the trade winds. Brief MVFR ceilings/mountain obscurations will
be possible through the afternoon. Clearing skies with offshore flow
at night. No AIRMETs posted this morning.

&&

.MARINE...
Expect trade winds to gradually decrease as a front drifts southward
into the area and stalls just north of Kauai late Monday. Winds will
become light and variable on Monday and continue through Tuesday. As
the front dissipates, high pressure will gradually build north of the
area and we should see breezy trades return by the end of the week.

Surf along north-facing shores will steadily lower through Monday
as a north swell that peaked early Friday fades. A moderate, short
to medium-period north to north-northeast swell will arrive Monday
night, then peak Tuesday night and gradually decline through the rest
of the week. Surf along select east-facing shores should see some
moderate surf from the north-northeast swell aforementioned above.
Otherwise, the lack of fresh to strong breezes upstream of the state
will continue to produce minimal windswell through the middle of next
week. Fresh to locally strong trades returning towards the end of the
week should bring the return of rough and choppy waves along east facing
shores. A small south-southeast swell should continue to produce some
small surf along south facing shores through today. Mainly background
swells are expected for the upcoming week with mainly a combination
of short-period southeast and background medium to long-period south-
southwest swells. We should see a small, long- period south-southwest
swell this weekend.

&&

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

&&

$$

DISCUSSION...TS
AVIATION...Foster
MARINE...Powell