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Hawaiian Islands Synoptic Discussion and Guidance

086
FXHW60 PHFO 231937
AFDHFO

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

.SYNOPSIS...

Trades will strengthen today, becoming locally strong this evening
through tonight then gradually settling into the moderate to
locally breezy range during early to mid-week. Stable and dry
conditions are expected through the forecast period.

&&

.DISCUSSION...

Quiet and relatively dry weather is anticipated through the
forecast period. For today, trades will gradually strengthen in
response to low pressure passing southeast of the Big Island.
Although the islands will not be within the wind radius of the low
itself, the tightening pressure gradient will be enough to
support locally strong trades this evening through tonight,
especially over the eastern end of the state. During this time,
an increasingly dry airmass will make inroads into the forecast
area coincident with rapidly increasing stability beneath a
building mid-level ridge. Existing clouds, mainly over windward
areas, will decrease in coverage this afternoon into tonight as
inversion heights fall to 5kft or lower. Nothing more than a
passing isolated light shower is expected over any of the windward
zones during the next 30 hours or so. Leeward zones will be dry,
save for typical afternoon showers over upslope portions of
Leeward Big Island. Once the low transitions to more of an open
wave and departs to the south, trades will settle into the
moderate to locally breezy range for Tuesday and Wednesday. At
the same time, a slight increase in trade wind showers over the
windward zones will be possible as slightly deeper moisture
advances toward the islands from the east, but prevailing high
stability will continue to limit shower coverage and rainfall
amounts.




&&

.AVIATION...

A band of low clouds and showers remains anchored across Kauai,
which continues to generate lowered cigs and isolated reduced
vsby this morning. Otherwise, satellite also shows an area of
low/mid lvl mstr lingering north of the state, while trade wind
clouds develop and expand in areal coverage along windward side of
the island chain. The latest radar trends shows only isolated
weak returns, mainly confined between and along islands in low
level convergent flow.

Surface ridge will remain anchored over the islands to begin the
work week reinforcing easterly trades, which will focus showers
and cloud cover along favored windward slopes into Monday. Mainly
VFR conditions continue, however a brief period of MVFR cigs are
possible in developing trade wind showers.

AIRMET Sierra for Tempo Mountain Obscuration remains in effect
across Kauai, as remnant low cigs and brief periods of reduced
visibility linger in the area. Satellite shows some breaks in the
dense clouds, so adjustments may be needed later this afternoon.

&&

.MARINE...

Moderate to locally strong trade winds will persist into
Wednesday, then decline and shift out of the southeast Thursday
into next weekend. A surface ridge will remain about 250 nm north
of Kauai into tomorrow, and the pressure gradient over the
islands will be strong enough to drive winds at border line Small
Craft Advisory (SCA) strength over the typically windy waters
around the Big Island and Maui. A dissipating surface low dropping
southward just east of the offshore waters will help to maintain
the current gradient and wind strength, even as the surface ridge
erodes late Monday. Surface high pressure will pass far north of
the islands Tuesday and Wednesday and likely maintain border line
SCA strength winds over the same waters. As the high moves off to
the east Thursday and Friday, its trailing ridge will be pushed to
near Kauai, causing winds to ease and shift out of the southeast
over most waters.

After a peak well above guidance yesterday, a declining northwest
swell will maintain High Surf Advisory (HSA) level surf along
exposed north and west facing into tonight. A reinforcing pulse of
northwest swell is expected overnight and may maintain large surf
into Monday, though the HSA currently runs through tonight.
Northwest swell will drop well below seasonal average from Tuesday
through Thursday. Another northwest swell arriving Friday could
push surf near the HSA level through Saturday.

East shore surf will be at or above seasonal average for the next
few days. A rare and compact subtropical gale formed far
northeast of the state several days ago, and this feature has been
generating a swell that will fill in today, peak on Monday, and
decline on Tuesday. We will keep a close watch on the PacIOOS
buoys, but for now, HSA level surf is not expected for east facing
shores. By midweek, expect short period trade wind swell to
produce east shore surf below seasonal average.

&&

.HFO WATCHES/WARNINGS/ADVISORIES...
High Surf Advisory until 6 AM HST Monday for Niihau-Kauai
Leeward-Waianae Coast-Oahu North Shore-Maui Windward West-Kona-
Kohala-Kauai North-Molokai Windward-Molokai North-Molokai West-
Maui Central Valley North-Windward Haleakala.

Small Craft Advisory until 6 PM HST Monday for Maalaea Bay-
Pailolo Channel-Alenuihaha Channel-Big Island Leeward Waters-Big
Island Southeast Waters.

Small Craft Advisory until 6 PM HST this evening for Kauai
Northwest Waters-Kauai Windward Waters-Kauai Leeward Waters-
Kauai Channel-Oahu Windward Waters-Oahu Leeward Waters-Kaiwi
Channel-Maui County Windward Waters-Maui County Leeward Waters-
Big Island Windward Waters.


&&

$$


DISCUSSION...JVC
AVIATION...SWR
MARINE...Wroe

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



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