100
FXHW60 PHFO 231302
AFDHFO

Area Forecast Discussion
National Weather Service Honolulu HI
302 AM HST Mon Sep 23 2024

.SYNOPSIS...
Moderate trade winds will prevail today as the surface ridge to
the north remains weak. Rainfall will favor windward and mauka
locations, but a few showers, some heavy, may develop across
leeward areas as a disturbance aloft moves overhead. Locally
breezy trades and more stable conditions will return Tuesday and
persist through the weekend.

&&

.DISCUSSION...
Currently at the surface, a ridge of high pressure is located
around 900 miles north of Honolulu, with broad but weak troughing
present between the ridge and the Hawaiian islands. Aloft a
closed upper low can be seen in water vapor imagery around 100 to
150 miles to the north of Oahu and Kauai. The broad surface
troughing has kept the pressure gradient a bit weaker than normal,
with generally moderate trade winds blowing across the island
chain early this morning. Infrared satellite imagery partly to
mostly cloudy conditions in windward areas, with partly cloudy
skies in most leeward locales. Radar imagery shows scattered
showers moving into windward slopes and coasts, with a few of
these showers reaching leeward communities at times. Main short
term focus is on rain chances and trade wind trends.

The broad trough of low pressure over and north of the state will
gradually dampen out and shift westward during the next couple
days. Moderate trades will prevail today with localized sea
breezes developing in some of the more sheltered leeward areas
this afternoon. The trades will increase a bit tonight and hold
at moderate to locally breezy levels Tuesday through Friday. The
trades may ease a bit this weekend as the ridge to the north
weakens.

As for the remaining weather details, the airmass will remain
unstable with the upper level low near the western islands today
and tonight. This will allow some more robust showers to move in
on the trades and produce brief downpours. Additionally, some
locally heavy showers could develop in leeward areas with the
assistance of sea breezes during the afternoon and early evening
hours, before fizzling out overnight. A mid-level ridge building
in from the east will bring a more stable airmass to the islands
Tuesday through Thursday. This should result in a return to
typical trade wind weather featuring mainly windward and mauka
showers. Another disturbance aloft could bring a slight increase
in trade wind showers Friday through the weekend.

&&

.AVIATION...
Moderate trades will usher in low clouds and showers to windward
and mauka areas, with a few showers occasionally spilling over to
leeward sides. Sea breezes will develop along some wind-protected
areas this afternoon, leading to low cloud and shower development
over those areas. Then trades will strengthen slightly heading
into tomorrow.

MVFR conditions can be expected in any showers. Otherwise, VFR
should prevail.

No AIRMETs are in effect. AIRMET Sierra for tempo mountain
obscuration may be needed tonight for the eastern end of the
state as a plume of moisture rides in on the trades.

&&

.MARINE...
High pressure generally north of the state will drive moderate to
locally fresh trades today. High pressure northwest of the islands
will strengthen through the middle of the week. This will produce
fresh to locally strong trades from Tuesday through the remainder
of the week. A Small Craft Advisory may be necessary for the windier
waters surrounding Maui County and Big Island Tuesday.

Surf along north and west-facing shores will remain very small
today. A small to moderate size, long to medium period northwest
swell (330 degrees) is timed to arrive Tuesday from a passing
North Pacific cold front. This swell will increase mid week north-
facing shore surf to well above head high along reefs and
shorelines where northwest energy is best focused. North shore
surf is expected to remain well under the High Surf Advisory
levels. South-facing shore surf will remain small as a mix of
small, medium period southwest swells pass through the next few
days. Eastern shore waves will remain small in response to recent
light trades. An upward trend in eastern chop will occur later
today and will persist through the week in response to
strengthened trades.

&&

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

&&

$$

DISCUSSION...Jelsema
AVIATION...Farris
MARINE...Blood