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RH7 %
WindNNE 12 mph
RoadOpen (4x4)
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Hawaiian Islands Synoptic Discussion and Guidance

320
FXHW60 PHFO 231337
AFDHFO

Area Forecast Discussion
National Weather Service Honolulu HI
337 AM HST Sun Jan 23 2022

.SYNOPSIS...
A high pressure system passing from west to east just north of the
region will keep moderate to locally breezy trade winds in the
forecast this weekend. An upper level ridge over the state will
keep fairly stable weather conditions in the forecast for most
areas through Monday. A low level trough moving in from the east
will increase shower trends for the windward Big Island and Maui
on Tuesday. Another high pressure system passing by north of the
islands on Wednesday and Thursday will keep moderate trade winds
blowing with brief showers possible, favoring windward and
mountain areas in a fairly stable trade wind regime.

&&

.DISCUSSION...The satellite imagery this morning shows cloud
bands associated with an old frontal boundary drifting into the
northwestern islands on the moderate to locally breezy trade
winds. A high pressure system is passing by just north of the
region. A cold front currently located far northwest of the state
will stall north of the island chain on Wednesday with no weather
impacts expected with this system.

In the short term forecast, the lingering clouds north of the
state from an old dissipated cold front will produce brief
showers drifting in on the trade winds over Kauai and Oahu today.
These showers will mainly affect windward and mountain areas of
both islands.

Otherwise fairly stable weather trends are expected through the
week in a continued moderate to locally breezy trade wind weather
pattern. An upper level ridge over the islands will keep trade
wind inversion heights on the low side around 4000 to 7000 feet
through Monday. This inversion will tend to cap vertical cloud
heights and decrease shower activity.

A low level trough will drift into the eastern islands on Tuesday
and Wednesday, increasing inversion heights and shower activity
across the state, with highest shower coverage forecast along the
windward slopes of the Big Island and east Maui.

The extended range forecast guidance from Thursday onward continues
to show a weak upper low developing just east of the Big Island.
This upper low may increase trade wind shower trends on Thursday
and Friday across the region. These increasing cloud and shower
trends would favor the typical windward and mountain areas.

&&

.AVIATION...
Moderate trade winds will dominate through the forecast period.
Patchy broken to overcast low clouds upwind from the state will
affect windward portions of the islands today. AIRMET Sierra for
Tempo Mountain Obscuration remains in effect across Kauai, and may
need to be expanded later today as more areas become affected by
the low cloud area.

&&

.MARINE...
Moderate to locally strong trades have returned and will hang
around through much of the week. These winds combined with large
seas associated with a west-northwest swell moving through have
led to Small Craft Advisory conditions for all Hawaiian waters,
which will continue through much of the day today before dipping
below as the swell moves out. Trades will shift to a more
northeast direction tonight through Tuesday as the islands become
positioned between a gale passing to the southeast and the ridge
to the north.

Surf along exposed north and west facing shores will gradually
lower through the day as the west-northwest swell that peaked
Saturday begins to move out. Offshore buoy observations this
morning extrapolated to the islands support the transition from a
warning to an advisory. Expect the advisory-level surf to hold
into Monday as a new, long-period west-northwest pulse arrives
tonight. Heights will then dip below advisory levels for north
and west facing shores Tuesday through midweek.

For the extended, guidance shows a powerful system lifting
northeast from Japan to the western Aleutians Monday through
Wednesday, with a decent sized area of gale- to hurricane-force
winds focused at the islands. Given the distance away from the
islands and the quick northeast track, confidence remains low at
this time. If it does materialize, a long-period, west-northwest
swell will be expected by or come Friday, that will linger into
next weekend.

Surf along east facing shores will rise today in response to an
easterly swell arriving from a gale positioned around 650 NM east
of Hilo. Morning observations at the Hilo buoy reflect this and
have picked up within the 8-12 second bands. Guidance has this
easterly swell lingering through Monday before easing into
midweek.

&&

.HFO WATCHES/WARNINGS/ADVISORIES...
High Surf Advisory until 6 AM HST Monday for north and west facing
shores of Niihau, Kauai, Oahu and Molokai, including north facing
shores of Maui and west facing shores of the Big Island.

Small Craft Advisory until 6 PM HST this evening for all Hawaiian
waters.

Small Craft Advisory until 6 PM HST Monday for windier waters and
channels around Maui and the Big Island.

&&

$$

DISCUSSION...Bohlin
AVIATION...Powell
MARINE...Gibbs

Bulletins, Forecasts and Observations are courtesy of Honolulu National Weather Service Forecast Office