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Temp2.5 C
RH20 %
WindNNE 41 mph
RoadOpen (4x4)
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Hawaiian Islands Synoptic Discussion and Guidance

172
FXHW60 PHFO 241322
AFDHFO

Area Forecast Discussion
National Weather Service Honolulu HI
322 AM HST Mon Jan 24 2022

.SYNOPSIS...
A rather dry and stable airmass will prevail over the islands
through much of the week, with a few showers affecting mainly
windward slopes and coasts. Moderate to locally breezy trades
will prevail through Wednesday, before easing Thursday and Friday
allowing for daytime sea breezes and overnight land breezes
across most of the state. An approaching front could bring an
increase in south to southeast winds and potentially some wet
weather to the islands by the end of the weekend.

&&

.DISCUSSION...
Currently at the surface, a 1007 mb low is located around 650
miles east-southeast of Hilo, while a 1023 mb high is centered
around 950 miles northeast of Honolulu. The resulting gradient is
producing moderate trade winds, strongest over the eastern end of
the state. Infrared satellite imagery shows clear to partly
cloudy skies in most areas, with a bit more cloud cover in some
windward locales. Radar imagery shows a few light showers over
windward Kauai, with very little rainfall elsewhere. Main short
term focus revolves around rainfall and trade wind trends during
the next several days.

The low east-southeast of the state will gradually weaken as it
slides southwestward during the next couple days, before opening
up into a trough Tuesday night and Wednesday as it slides by well
to the south of the island chain. At the same time ridging will
hold in place to the north of the area, keeping moderate trade
winds in place, which may be locally breezy over the eastern end
of the state at times. A front approaching and eventually
stalling out a couple hundred miles northwest of the islands
Thursday and Friday, will push the ridge southward and closer to
the state. This is expected to shift boundary layer winds east-
southeasterly, resulting in a light and variable wind pattern
featuring daytime sea breezes and overnight land breezes across
the western islands, while light to moderate trades hold over the
Big Island and Maui. A new front approaching from the northwest
could bring an increase in southeast to south winds over the
weekend.

As for the remaining weather details, a very dry and stable
airmass has overspread most of the state early this morning, with
precipitable water values below 1 inch and inversion heights
settling around 5 kft. There remains some lingering moisture
associated with and old front over Kauai where a few showers
continue to affect windward slopes and coasts, but drier air is
moving in quickly and should encompass the Garden Isle by
daybreak. After daybreak, very little if any shower activity is
expected statewide. We should see a slight increase in trade wind
showers focused mainly over windward terrain and coasts tonight
through Wednesday night as PW values tick up ever so slightly and
inversion heights get a very slight boost. Overall however, the
pattern will remain stable and much drier than normal. The rather
dry conditions should then continue Thursday through Saturday,
with east-southeasterly flow favoring a few windward showers
mainly during nights and mornings and perhaps a shower or two
developing over the island interiors each afternoon. Deeper
moisture may advect into the state from the south and west late
in the weekend into early next week, potentially bringing some wet
weather back to the island chain.

&&

.AVIATION...
Early morning surface analysis reveals high pressure northeast of
the state and a surface low southeast of the Big Island. The
pressure gradient between these two features will support moderate
to locally breezy easterly trade winds throughout the next 24
hours, particularly across the eastern end of the island chain.
Relatively stable, dry air will limit clouds and shower activity
today, though any showers that do form will favor north through
east facing slopes and coasts. VFR flight conditions are expected
to prevail at most locations, though brief periods of MVFR cigs
will be possible in developing trade wind showers.

AIRMET Tango remains in effect for moderate low-level turbulence
downwind of the mountains of the Big Island, Maui, and Molokai.
This AIRMET will likely remain in effect through at least tonight.

&&

.MARINE...
A high pressure ridge north of the region will continue to produce
moderate to locally strong trade winds over the Hawaii region into
Wednesday, and then winds will veer out of the southeast
direction from Thursday into the weekend. Trade winds will remain
strong enough with elevated seas for continued Small Craft
Advisories (SCA) over most waters and channels today. A
dissipating surface low southeast of the Big Island will continue
to drift south and help maintain the trade wind strength between
the high pressure ridge and the low center. A surface high
pressure system will pass far north of the islands Tuesday and
Wednesday and likely maintain border line SCA strength winds over
the same waters. The high moves off to the east on Thursday and
Friday, causing winds to ease and shift out of the southeast over
most waters.

As one northwest swell continues to fade, an overlapping new
northwest swell builds into the region maintaining High Surf
Advisory (HSA) conditions along exposed north and west facing
shores through this afternoon. The current HSA was extended for
exposed north and west facing shores through this afternoon. Swell
heights remain 1 to 2 feet above wave model guidance. Northwest
swell heights will then decline from Tuesday through Thursday.
Another northwest swell arriving Friday could push surf heights
back near HSA levels through Saturday.

East shore surf will be at or above seasonal average today. 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 peak today, and then decline later tonight
through Tuesday. By midweek, expect short period trade wind swell
to produce east shore surf below seasonal averages. Surf heights
along south facing shores will remain small through the week.

&&

.HFO WATCHES/WARNINGS/ADVISORIES...
High Surf Advisory until 6 PM HST this evening 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 this evening for Kauai
Northwest Waters-Kauai Windward Waters-Kauai Leeward Waters-
Kauai Channel-Oahu Windward Waters-Kaiwi Channel-Maui County
Windward Waters-Maalaea Bay-Pailolo Channel-Alenuihaha Channel-
Big Island Windward Waters-Big Island Leeward Waters-Big Island
Southeast Waters.

&&

$$

DISCUSSION...Jelsema
AVIATION...Vaughan
MARINE...Bohlin

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