Gale Warning 515, NWS Anchorage, AK

Southcentral and Southwest Alaska Forecast Discussion...CORRECTED
National Weather Service Anchorage AK
728 PM AKDT Tue Sep 13 2022

.ANALYSIS AND UPPER LEVELS...

The parent low of the system over Mainland Alaska this afternoon
is vertically stacked near Bethel. There is not much punch left
with this system but just enough moisture and lift due to cold air
aloft to keep showers peppered across Southwest Alaska. A more
significant upper level low developed in the northern Gulf and
can be seen on satellite tracking from Prince William Sound into
the Copper River Basin this afternoon. The heaviest rainfall in
Southern Alaska is associated with this upper low. The next upper
level low is digging southward dover the Kamchatka Peninsula and
interacting with the jet stream. This is rapidly intensifying a
low just east of Kamchatka and should spin it up to a storm force
low by tomorrow. The rising star of the weather show is Typhoon
Merbok which is close to 30N 160E this afternoon. It will become
the big weather system impacting the region for the second half of
this week.

&&

.MODEL DISCUSSION...

Models in reasonable agreement through the week. In the short
term, there is just a few differences in the weak waves moving
from south to north over Southcentral Alaska but nothing that will
really change the forecast. The low tacking across the northern Bering
Sea tonight through Thursday is handled well by the models though
the ECMWF is a bit of an outlier by Thursday where it has the low
tracking farther to the southeast than any other model.
The real issue is with the remnants of Typhoon Merbok as it heads
into the Bering Sea for the second half of the week. With this
deep tropical system, the models are having some difficulty with
the track and strength. They are in usable condition, but the
differences are not trivial. What is knows in that there will be
very strong winds and very high seas across the entire Bering Sea
alter this week. It is just the details of exactly where and how
high.

&&

.AVIATION...

PANC...A south-southeast wind is expected to move into the
airfield early this evening and persist through Wednesday
afternoon. Showers should diminish overall overnight with just
some occasional ones moving over the area. Some of those pesky
MVFR ceilings may occur occasionally through the night, but
conditions should remain generally VFR.

&&

.SHORT TERM FORECAST SOUTHCENTRAL ALASKA (Days 1 through 3)...

A fairly unsettled weather pattern will continue across
Southcentral Alaska over the next few days as a series of upper
level waves move across the area. These upper level waves will
continue to bring rain and showers across the area. The rain will
be intermittent across the area and some pokes of sunshine are
also possible, especially in the lee of the Chugach Mountains. A
15-20 kt Turnagain Arm wind will develop this evening, peak early
Wednesday morning and then ease Wednesday afternoon. These winds
may intermittently bend into Anchorage due to up-inlet flow
expected during this period. Patchy fog is also likely in Prince
William Sound Wednesday night into early morning due to light
winds and favorable conditions for fog development.

&&

.SHORT TERM FORECAST SOUTHWEST ALASKA (Days 1 through 3: Tonight
through Friday)...

A vertically stacked low currently positioned near Quinhagak is
weakening as it shifts southward. The shower activity rotating
around the low will slowly taper off overnight from north to
south. By early Wednesday, we will see a brief break of drier
weather as a transient ridge of high pressure builds overhead. The
next weather maker will be an upper trough and surface low
pressure setting up over the northern Bering Sea, advancing a
front eastward toward western Alaska. Along and ahead of the
front, steadier widespread rain with southerly winds arrives
Wednesday afternoon and continues through the day Thursday.
Daytime highs will mostly be in the mid 50s and overnight lows in
the low 40s under cloudy skies. The front exits the area by late
Thursday night with decreasing rain coverage and diminishing
winds. For Friday and into the weekend, another front pushing
ahead of a new Bering Sea low brings the next round of rain and
gusty south-southwesterly winds.

&&

.SHORT TERM FORECAST BERING SEA/ALEUTIANS (Days 1 through 3:
Tonight through Friday...)

A weakening low pressure system over the Kuskokwim Delta is
slowly moving southward. Areas of small craft winds wrapping
around the backside of the low over the eastern Bering Sea
continues to track eastward with the low. The winds are expected
to subside by tonight along with rain tapering off as a transient
ridge of high pressure builds overhead. Meanwhile, an upper trough
and surface low pressure sets up over the northern Bering Sea,
advancing a front eastward toward western Alaska. Between tonight
and Wednesday, rain with small craft winds will occur along the
leading edge of the front as it crosses the western Bering Sea and
Aleutians Islands. As the front pushes east Wednesday evening,
storm force to gale force winds wraps around the backside of the
low as it approaches Saint Matthew Island.

Attention then turns to Typhoon Merbok, transitioning to an
extra- tropical low pressure system as it moves from the West
Pacific Ocean into the Bering Sea from Thursday to Saturday.
Initially, winds will be south to southwest out ahead of the low,
then switching to the west as the low passes to the north. Some
uncertainty remains regarding the exact track and intensity, which
could affect where the strongest winds occur. The current
forecast shows the core of strongest winds in an area from Attu
Island to Adak with the winds peaking early Friday morning.
Therefore, a High Wind Watch has been issued from Thursday evening
through Friday morning for the Western and Central Aleutians. The
winds should begin to slowly diminish through the day Friday for
the regions as the surface low lifts northward.

For Friday through the weekend, the heaviest rain and strongest
winds will be over the entire Bering Sea, including the potential
for the Pribilof Islands to experience storm to hurricane force
winds. Any shift in the track or change in the intensity could
alter the trajectory of the core of strongest winds. Nonetheless,
this is a significant storm that will be closely monitored, so
stay tuned for updates.

&&

.MARINE...

The big marine issue for the second half of this week will be
Typhoon Merbok.It will weaken under typhoon force before it gets
to the Bering Sea, but will rapidly re-intensify and go through
the extra-tropical transition as it ingests cold air from eastern
Russia Wednesday night. There is still some uncertainty as to
the exact track and strength of this storm as it moves through
the Bering, but the center of the low should pass between Adak and
Attu sometime Thursday, though it is looking like closer to Attu
at this time. Regardless, it will then track from the Western
Bering Sea to the vicinity of Norton Sound on Saturday. Expect
widespread storm force winds across the Bering with areas of
hurricane-force winds. The hurricane-force winds are most likely
from the Western Aleutians to the Central Bering Sea between
Thursday night and Friday night. Seas are also expected to build
rapidly with widespread 30 to 40 ft seas across the Bering with 40
to 50 ft seas associated with the strongest winds. This will be a
major Bering Sea Storm and mariners are encouraged begin
preparing for it now.

&&

.LONG TERM FORECAST (Days 4 through 7: Saturday through Tuesday)...

Fall has arrived and with it comes unsettled conditions across
Southern Alaska through the extended period, with brief reprieves
provided by weak transient ridging. Several bouts of intense
winds and rainfall expected for both Southwestern Alaska and
Southcentral.

By Friday evening, the remnants of Typhoon Merbok will have made
its way across the Aleutians and be bearing down on Southwest
Alaska. Heavy winds and rainfall associated with this low will be
of concern across the Bering with heightened focus on the Central
Aleutians, Pribilofs, Nunivak Island, and Southwest Alaska through
Sunday afternoon. Southwesterly gales, storm-force, and areas of
hurricane-force winds possible Saturday morning expected to
slowly ease into Sunday evening. Model discrepancies aggravate
forecasting the core of highest winds. Tuesday 12Z Canadian model
advances the storm into the Y-K Delta early Saturday morning, while
GFS and Euro solutions pull the storm motion more to the north,
focusing the winds over Nunivak Island. Either solution still
represent favorable conditions for high surf and coastal flooding
along the Southwest coast for the early weekend. Precipitation and
winds associated with the remnants of Merbok expected to slowly
diminish Sunday.

From Sunday morning, a respite in precipitation for Southcentral
is expected to persist through Monday afternoon. With some
discrepancies, guidance then suggests the introduction and
intensification of a North Pacific low south of the Alaska
Peninsula, to move northeastward towards Southcentral. This system
will provide strong precipitation across the Southcentral
coastline pushing inland. Precipitation associated with this
system expected to persist through Tuesday. As the system
approaches Kodiak Island, southeasterly flow promotes the
development of Barrier jet winds from Yakutat to the Prince
William Sound Tuesday morning.

&&

.AFC WATCHES/WARNINGS/ADVISORIES...
PUBLIC...High Wind Watch 187 191.
MARINE...Storm Warning 185 411 412.
 		 Gale Warning 181 413.
FIRE WEATHER...NONE.

&&

SYNOPSIS AND MODEL DISCUSSION...EZ
SOUTHCENTRAL ALASKA...ED
SOUTHWEST ALASKA/BERING SEA/ALEUTIANS...MF
MARINE/LONG TERM...CL