FXAK68 PAFC 291331
Southcentral and Southwest Alaska Forecast Discussion
National Weather Service Anchorage AK
531 AM AKDT Thu Sep 29 2022
.ANALYSIS AND UPPER LEVELS...
An upper trough, which spans from the Bering Sea into
Southcentral, is becoming stretched meridionally this morning. An
embedded low over the eastern Bering and located on the upstream side of
the upper trough is digging southward along the Southwest coast.
Meanwhile, a smaller trough located over Kodiak Island and on the
downstream side of the upper trough is beginning to lift northward
into Southcentral. The smaller trough is following in the wake of
an occluded front, which moved inland of the Gulf coast during
the overnight hours. Scattered showers over Prince William Sound
and the Kenai Peninsula are getting shunted northward with the
front`s northward progress while, offshore, strong easterly winds
have been noted with a lingering barrier jet. Buoy 61 has observed
winds gusting to near 60 mph while buoy 82`s observed winds have
been slightly milder with gusts to only 45 mph. These winds should
steadily diminish through the morning hours with the departure of
the front to the north. This will be true for down-inlet flow
through Cook Inlet into the Shelikof Strait. Otherwise, clouds and
low stratus blanket much of the coast, as well as Kodiak Island,
while clearer conditions are noted further offshore.
Strong cold air advection and an enhanced pressure gradient over
the eastern Bering Sea are maintaining small craft to gale force
northerly winds. The axis of stronger winds stretches from east of
Saint Matthew Island, southward, to east of the Pribilofs, and into
Bristol Bay. These winds should gradually relax throughout the
rest of the day as the upper trough shifts further east. A hurricane
force low is quickly approaching the Western Aleutians. Increasing
southeasterly winds to hurricane force will precede the low
followed by southwesterly hurricane force winds later tonight. The
threat for seas ranging from 35 to 45 feet will exist by tonight
as a result.
Models continue to come into better agreement with a hurricane
force low entering the Bering over the next few days. All guidance
takes the low immediately west of the Aleutians while also
showing the low peaking in intensity later this evening. From
there models depict the low undergoing a weakening trend while
also decelerating in forward speed, which puts the low near or
over the Pribilof Islands early Sunday morning as much weaker
system. A new Kamchatka low is forecast to emerge into the western
Bering Sea Saturday night. Models are in poor agreement with the
timing and strength of the low at this time.
PANC...VFR conditions and light winds are forecast through the
period though showery conditions could potentially bring ceilings
to MVFR levels at times. There is some uncertainty with Turnagain
Arm winds bending into PANC later this afternoon, though these
winds should remain below 10 knots.
.SHORT TERM FORECAST SOUTHCENTRAL ALASKA (Days 1 through 3/Today
through Saturday night)...
A steady supply of upper level short-waves will track northward
across Southcentral through tonight, resulting in fairly widespread
rain showers. An upper level low and short-wave digging down the
back side of the long-wave trough will interact with a front over
the eastern Gulf and Pacific Friday-Friday night, leading to a
rapidly moving low across the eastern Gulf/Southeast Alaska and
into Canada. Rain with this system will clip at least the eastern
half of the the Copper River Basin, and perhaps as far west as the
eastern Prince William Sound, while showers diminish across the
remainder of Southcentral. Zonal flow behind the exiting upper
low/short-wave means the next long-wave trough will move in quickly,
with rain spreading to Kodiak Island Saturday then Southcentral
.SHORT TERM FORECAST SOUTHWEST ALASKA (Days 1 through 3: Today
through Saturday night)...
A weakening low stretched out along the Southwest coast will
begin to make southeastward progress today, eventually exiting
into the western Gulf later tonight. In the meantime, areas of
showers will continue to drift across much of the region as
smaller waves continue to pivot around the main upper low as it
drifts south. Most of this activity should diminish by tonight,
with even some areas of clearing possible over Bristol Bay.
However, it will likely be quite a chilly start for areas that are
able to radiate out efficiently with calming winds and the
decreasing cloud coverage, and lows could dip down to the low 30s
for spots like King Salmon early on Friday. Benign conditions will
persist into Friday as a transient ridge moves into place between
the departing Gulf low and the next item of interest soon
expected to impact much of the Bering out west.
By Friday evening, a very large, slow moving low drifting out
over the Bering will push its occluded front into the Southwest
coast and northern Alaska Peninsula (AKPen). This low will be a
remnant of current tropical storm Kulap, but neither the low nor
the front reaching the coast are expected to have notable impacts
beyond slightly increasing southerly winds and bands of rain
moving ashore. Kulap`s remnant low and weakening front will
continue to push areas of rain across Southwest through Saturday
evening as the storm`s center drifts very slowly east and
likewise becomes much weaker with time.
.SHORT TERM FORECAST BERING SEA/ALEUTIANS (Days 1 through 3:
Today through Saturday night)...
Relatively quiet conditions will persist this morning compared to
what will soon be affecting a large portion of the Bering Sea
starting later this afternoon. A corridor of northwest gales
pushing into the southern Alaska Peninsula (AKPen) and eastern
Aleutians will weaken through this evening as the supporting
pressure gradient relaxes and as cold air advection associated
with a cool air mass pushing south into the Pacific ceases.
Showers moving into the southern AKPen and eastern Aleutians will
begin to subside this evening as well as a shortwave ridge moves
into place ahead of the much more impactful feature of interest
moving into place to the west.
Looking back to the west, tropical storm Kulap is already visible
on Himawari satellite this morning as it barrels straight towards
the far southwest corner of the Bering. This system is expected to
undergo a transition to a post-tropical low just before it enters
the Bering near Shemya later this evening, but the powerful wind
field associated with this low will not lose much of its punch
once it gets here. Impacts to the far western Aleutians still look
very similar compared to previous assessments. A corridor of
Hurricane force southeast wind will first move in along the
system`s developing front, pushing past Shemya and Attu into the
western Bering this afternoon. This will be followed soon after
by a core of even stronger Hurricane force winds wrapping into the
south side of the low as the center continues northeast into the
western Bering. Winds in the Shemya and Attu area with the second
batch of winds should peak in the 60 to 80 mph range, with gusts
up around 100 mph still possible at the peak intensity late
tonight or very early Friday. A High Wind Warning remains in
effect starting Noon today through Friday for the western
From there on, the low should begin to weaken and slow down as it
becomes stacked and occluded, but it will take some quite some
time for the wind field to diminish. The low`s front will weaken
below gale force shortly after pushing past the Pribilofs and
Central Aleutians on Friday, with a quick period of rain also
moving past with the front. Persistent westerly winds will very
slowly weaken along the rest of the Aleutian Chain to the west,
but probably will not come down below gale force until sometime
late on Saturday night as the low begins to drift more east to
southeast and slowly spins down.
.LONG TERM FORECAST (Days 4 through 7: Sunday through Wednesday)...
An area of low pressure that was formerly Kulap moves across
western parts of the Alaska Peninsula and then weakens further as
it settles in the Gulf of Alaska on Sunday. As the low progresses
into the the Gulf, additional moisture brings a return of cool,
cloudy, and rainy conditions over Southcentral heading into early
next week. Widespread rain over Kodiak Island will push northward
from the Kenai Peninsula to Prince William Sound. Isolated to
scattered showers are possible further inland, but will be drier
due to downslope easterly flow. Meanwhile, a transient ridge of
high pressure provides a brief break of drier weather over
interior Alaska between Monday and Wednesday. Another storm
system, albeit weaker, crosses the Aleutians with the next round
of wind and rain and then enters the North Pacific midweek.
Unsettled weather continues into Tuesday as the next low and front
moves southeastward from the Kamchatka Peninsula. However, models
diverge significantly in the specific details towards the end of
PUBLIC...High Wind Warning: 191.
MARINE...Hurricane Force: 178, 411
Storm: 175, 177, 185, 412, 413
Gale: 155-170, 172-174, 176, 179-181, 414.
SYNOPSIS AND MODEL DISCUSSION...BL
SOUTHWEST ALASKA/BERING SEA/ALEUTIANS...AS