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Hawaiian Islands Synoptic Discussion and Guidance

445
FXHW60 PHFO 191535 CCA
AFDHFO

Area Forecast Discussion...CORRECTED
National Weather Service Honolulu HI
535 AM HST Wed Jan 19 2022

.SYNOPSIS...
The light background winds with dry and stable atmospheric
conditions will allow an afternoon sea breeze and nighttime land
breeze weather pattern to persist through early Friday. Expect
some cloud cover with a few showers over the islands each
afternoon, followed by clearing skies at night. As we head into
the weekend, it appears that a front moving down into the area
late Friday may increase low cloud cover and showers along
windward and mauka sections as northeasterly trade winds fill in
across the area through this weekend. Drier trade wind weather is
expected by early next week.

&&

.DISCUSSION...
A weak northeast to southwest oriented surface ridge is near the
western end of the island chain. Elsewhere, the tail end of a
dissipating frontal system appears to be about 340 miles north-
northwest of Lihue early this morning. The close proximity of the
surface ridge to the islands is producing light southeast to
south winds over the western end of the state, with relatively
weak east to southeast flow elsewhere. These gentle winds allowed
local land breeze circulations to set up over each of the
individual islands last evening. This cleared out most of the low
cloud cover from Oahu to the Big Island overnight. However, an
area of low clouds with some higher layered clouds has crept over
Niihau and Kauai early this morning. There are also some showers
embedded within some of these clouds.

Water vapor imagery shows a mid-tropospheric ridge over the
islands. This ridge aloft along with dry atmospheric conditions
will keep the stable weather pattern in place through early
Friday. There is slightly higher low-level moisture near Kauai,
but the other islands remain relatively dry. With the surface
ridge staying close to the state, the light background flow will
persist. This will allow alternating local afternoon sea breezes
and nighttime land breezes to become established over each of the
individual islands. The sea breezes will produce some low clouds
and a few showers each afternoon over the islands, followed by
clearing skies at night.

The forecast guidance continues to show that a new cold front
will approach the state from the northwest later this week. This
front is forecast to reach Kauai Friday night. After that the
guidance appears to indicate this feature may weaken rapidly
as it moves from Oahu to Maui County on Saturday. A new surface
high pressure system will build in behind the front, which will
cause locally moderate northeasterly trade winds to fill in across
the state this weekend. Expect low clouds and showers to increase
ahead of and along the front as long as it remains a viable
feature. Otherwise, the low-level trade wind flow will likely
bring increasing low clouds and brief trade showers over windward
facing sections of the state this weekend. Looking ahead, it
appears that a drier trade wind weather regime will become
established over most of the island chain by early next week.

&&

.AVIATION...
Light synoptic flow in the lower levels will allow local wind
effects to drive the weather. Land breezes and inland clearing
will give way to sea breeze development this afternoon. This will
drive cloud buildup and a few light showers over island interiors.
An increasingly stable air mass will limit most shower
development, though brief MVFR conditions are possible if any
develop. Otherwise, VFR will prevail.

No AIRMETs are in effect, nor expected through the forecast
period.

&&

.MARINE...
A surface ridge currently near Kauai and Oahu continues to
support light to locally moderate winds, favoring an E-SE
direction near the Big Island, and SE-S near Kauai. Little change
is expected through Thursday, but weak convergence associated
with a retreating front will support a few showers near Kauai
today. A different front, approaching Thursday night and Friday,
will cause the ridge to move S and weaken, resulting in light and
variable winds. High pressure passing N of the area over the
weekend will support moderate to locally fresh NE winds into early
next week. The high will likely push fragments of the front over
the area, leading to a brief increase in showers, mainly over
windward waters Friday and Saturday.

Winds are likely to remain below Small Craft Advisory (SCA)
thresholds through the forecast period, but combined seas larger
than 10 feet late in the week will require its issuance for most
zones. A building WNW swell will bring High Surf to exposed N and
W shores as it peaks today, including W facing shores of the Big
Island, and a High Surf Advisory is posted. This swell will
gradually diminish tonight into Thursday. A powerful long-period
WNW swell is expected to build Friday, peak Friday night/Saturday,
then gradually diminish Sunday/Monday. A High Surf Warning will
likely be necessary for exposed N and W facing shores, including
the W facing shores of the Big Island. A moderate ENE swell is
also possible over the weekend, generated by a developing gale-
force low that will be about 1000-1300 miles E of the islands the
next couple of days.

&&

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

&&

$$

DISCUSSION...Houston
AVIATION...TS
MARINE...Birchard

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



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