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000
FXHW60 PHFO 201335
AFDHFO

Area Forecast Discussion
National Weather Service Honolulu HI
335 AM HST Sat Apr 20 2024

.SYNOPSIS...
Moderate trade winds are forecast through the weekend with
enhanced showers decreasing from west to east through this
afternoon. Dry trade wind weather will continue on Sunday with
wind speeds starting to pick up slightly by Sunday night as a high
pressure system builds north of the islands. Brief periods of
showers will pass through the islands through early next week in a
moderate to breezy trade wind pattern. The middle of next week
will be on the wet side for most islands, especially in the
overnight to early morning hours, as a band of unstable clouds
moves in from the northeast.

&&

.DISCUSSION...
Satellite imagery this morning shows a sharp upper trough moving
into the northwest islands and a band of low clouds from an old
frontal boundary at the surface level. This upper trough will help
to enhance trade wind showers through the morning hours. An upper
ridge will build in behind this trough as it passes from west to
east across the state today, increasing stability and decreasing
shower coverage. Sunday will be the most favorable weather day of
the weekend for outdoor activities.

Strong winds aloft enhanced by this passing upper level trough
will continue to support High Wind Warning conditions for the
highest Big Island summits of Mauna Kea and Mauna Loa until this
evening. Winds at summit level will decrease quickly by around
Sunset as the upper trough passes east of the Big Island.

From Sunday night into Tuesday, a weak high pressure system will
build just north of the Hawaiian islands. Fair weather remains in
the forecast for most areas with a slight increase in our trade
winds from moderate into the moderate to breezy range should be
expected. One wrinkle in this forecast, no surprise to most locals,
is the Hilo side of the Big Island and portions of East Maui will
continue to see periods of enhanced showers.

From Tuesday night into Thursday morning, a band of unstable
clouds will move from northeast to southwest across all islands.
Expect increasing shower trends, favoring windward and mountain
areas especially in the overnight to early morning hours. Rainfall
coverage was increased for this time period in the morning
forecast grid package.

From Thursday onward, typical trade wind weather will continue
for the rest of the week with brief windward and mountain showers
possible.

&&

.AVIATION...
Light to moderate trade winds will persist through forty-eight
hours and beyond. Bands of low clouds and light showers off the
Pacific will impact mainly windward slopes and coasts. Isolated
spillover showers over leeward slopes of the smaller islands will
taper off later this morning. Partial clearing expected over
island interior`s in the afternoon.

AIRMET Sierra for mountain obscuration is currently in effect for
windward portions of all islands. Conditions are expected to
improve towards noon.

&&

.MARINE...
High pressure building in from the north-northwest will drift east
and keep trade winds moderate to fresh through the weekend. The
ridge of high pressure should rebuild early next week, which
should produce fresh to locally strong trade winds once again.

The current south swell will hold today than steadily decline
Sunday. A series of small, medium period swells will persist
through the weekend keeping south facing shores from going flat.
Small, short- period north swell will continue into the weekend.
A larger moderate medium period north swell reinforcement will
arrive late tonight. A rise in surf overnight is expected but the
north swell looks to peak Sunday well below High Surf Advisory
levels. Surf along east facing shores will remain small but can
expect a slight increase early next week as the trades strengthen.

&&

.HFO WATCHES/WARNINGS/ADVISORIES...
High Wind Warning until 6 PM HST this evening for Big Island
Summits.

&&

$$

DISCUSSION...Bohlin
AVIATION...Bedal
MARINE...Shigesato