Area Forecast Discussion
Issued by NWS Honolulu, HI

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FXHW60 PHFO 232023
AFDHFO

Area Forecast Discussion
National Weather Service Honolulu HI
1023 AM HST Mon Jan 23 2017

.SYNOPSIS...
High pressure northeast of the state will keep a light to moderate
trade wind flow in place through Thursday. The trades will
diminish Friday as a cold front approaches from the northwest. The
cold front will then sweep through the island chain over the
weekend, with breezy north to northeast winds expected Sunday
through early next week. Showers will favor windward and mauka
areas through the work week, with showers most prevalent today
through Tuesday as an upper level disturbance moves overhead. A
drier and more stable airmass will then limit shower activity
Wednesday through Saturday. Showers will then increase in
coverage over the weekend as the cold front moves through the
state, with a drier trade wind shower regime returning for early
next week.

&&

.DISCUSSION...
Currently at the surface, a 1031 mb high is centered around 900
miles northeast of Honolulu, with light to moderate trades in
place across Kauai and Oahu, and moderate to locally breezy trades
over Maui County and the Big Island. Aloft, a broad southwest to
northeast oriented upper level trough is evident in water vapor
imagery, with the axis running through the western end of the
island chain. Visible satellite imagery shows mostly cloudy skies
in place across windward areas, with partly cloudy or mostly clear
conditions in leeward locales. Meanwhile, radar imagery and rain
gauge observations show frequent showers moving into windward and
mauka areas, with isolated showers reaching leeward sections of
the smaller islands from time to time. Main short term concern for
the rest of the day revolves around rainfall trends.

Rest of today,
High pressure northeast of the state will weaken and shift
eastward, allowing the trade wind flow to ease a bit through the
afternoon hours. Remnant moisture associated with the front which
moved through the islands this past weekend, is already beginning
to lift northward into the Big Island and Maui County. Meanwhile,
precipitable water values are also rising over the western
islands due to persistent east-northeasterly trades. The increase
in moisture along with the upper level trough elevating inversion
heights should keep showery weather in place across windward and
mauka areas through the day, with isolated showers reaching
leeward areas as well. The most frequent shower activity is
expected over the eastern end of the island chain this afternoon,
in the region of best forcing for ascent ahead of the upper level
trough axis.

Tonight and Tuesday,
Light to moderate trade winds will continue across the state
through the period as high pressure remains nearly stationary
northeast of the island chain. The upper level trough axis will
remain over the eastern end of the state tonight, then shift
slowly eastward and away from the Big Island on Tuesday. Showers
are expected to favor windward and mauka areas through the period,
with showers most prevalent over the eastern end of the state in
closest proximity to the upper level trough.

Tuesday night through Friday night,
High pressure northeast of the islands will keep light to moderate
trade winds in place through Thursday. The trades will then
diminish Thursday night through Friday night as a cold front
approaches from the northwest, with land and sea breezes expected
in many areas. Aloft, mid and upper level ridging will build
eastward over the state Tuesday night and remain over the islands
through Friday night. As a result, we should see a decrease in
trade wind showers beginning Tuesday night, with a drier and more
stable airmass expected to overspread the state Wednesday through
Friday night. Showers are expected to be limited primarily to
windward and mauka areas through the period.

Saturday through next Monday,
The GFS and ECMWF are in good agreement showing a cold front
approaching Kauai from the northwest late Saturday afternoon,
then pushing southward down the island chain Saturday night and
Sunday. High pressure is then expected to build northwest of the
state Sunday night through early next week. A fairly dry and
stable pattern is expected to remain in place on Saturday, with
showers then increasing in association with the front Saturday
night and Sunday as it moves through the area. A drier trade wind
shower regime is then expected to return for early next week.

&&

.AVIATION...
An upper level trough over the Hawaiian Islands will enhance
clouds and shower activity in east to east-southeast flow today.
Expect tempo MVFR cigs with showers with mountain obscurations
over northern and eastern sections of most islands. Isolated MVFR
cigs are expected elsewhere.

AIRMET SIERRA for tempo mountain obscuration over northern and
eastern sections of Oahu, Molokai, Maui and the Big Island remains
in effect.

&&

.MARINE...
A strong high northeast of the area is maintaining strong
easterly trade winds across some areas of the Hawaiian waters.
Also, in some areas seas remain above 10 feet. Please see the
latest Marine Weather Message, MWWHFO, for further details. The
Small Craft Advisory may need to be extended for some areas
overnight.

The strong trade winds and a short-period north swell continue to
produce surf above the High Surf Advisory (HSA) level on east
facing shores of most islands. The HSA will likely stay up
through this evening.

A large northwest swell will likely produce surf well above the
advisory threshold along north and west facing shores of the smaller
islands from Tuesday through Thursday morning. Another large
northwest swell may produce advisory-level surf along north and west
facing shores of the smaller islands starting Friday night and
continuing into next weekend.

&&

.HFO WATCHES/WARNINGS/ADVISORIES...
High Surf Advisory until 6 PM HST this evening for Kauai
Windward-Oahu Koolau-Olomana-Molokai Windward-Maui Windward West-
Windward Haleakala-Big Island North and East.

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

&&

$$

DISCUSSION...Jelsema
AVIATION...Bohlin
MARINE...Evans


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