Gale Warning 542, NWS Anchorage, AK

Southcentral and Southwest Alaska Forecast Discussion
National Weather Service Anchorage AK
527 AM AKDT Fri Sep 30 2022

.ANALYSIS AND UPPER LEVELS...

A hurricane force low, the remnants of Kulap, has pushed into the
western Bering Sea this morning and bottomed out at around 943 mb
north of Attu. Morning ASCAT passes revealed a large area of
storm force winds to the south and southwest of the center of the
low, extending into the Western Aleutians. Given the strength and
size of the low, hurricane force winds are likely embedded within
the wind field. However, there is a lack of meaningful
observations in that region and buoy 35 remains too far east of
the low's center. Shemya has reported a sustained wind of 57
knots, but also remains further south of the strongest winds. A
front extends from the center of Kulap, currently located 144 nm
north of Shemya, and extends southeastward into the Central
Aleutians. Gales with higher gusts are ongoing along the front.
The approach of the low into the Bering has induced ridging over
the eastern Bering Sea, which has resulted in widespread low
stratus and areas of fog to the Kuskokwim Delta coast and
southward across Cape Newenham and to just east of Nelson Lagoon.

Further east and across Southcentral, what remains of an occluded
front has slowed considerably just inland of the Gulf coast.
Numerous showers have been impacting Prince William Sound and much
of the Anchorage Bowl and Mat-Su Valleys through the overnight
hours. The Gulf has been experiencing relatively clear conditions
in the wake of the front and in advance of the next trough, which
is expected to track generally eastward through the southern Gulf
as an open wave through Saturday. A trough of low pressure is
lifting northward and will overspread the eastern Gulf throughout
the day. Otherwise, winds across Southcentral have been
surprisingly calm, which has prompted the development of fog and
low stratus over portions of Anchorage all the way up into
Talkeetna.

&&

.MODEL DISCUSSION...

Models are in good agreement today and tomorrow with the
progression of a strong low moving over the Pribilofs by Sunday
morning. Models begin to diverge thereafter. Previous
deterministic runs of the CMC and EC were mostly in line with each
other taking the low southeastward toward Bristol Bay Sunday
night while the GFS remained an outlier and took the low further
north and into Northwest Alaska. Latest deterministic runs have
come into somewhat better agreement this morning with the low
weakening into an open trough and pivoting northward across
interior Alaska through Sunday night. The GFS is still the
furthest north with this feature and somewhat stronger at 990 mb;
however, the EC and CMC have started to come on board with a more
northerly solution, albeit weaker, and pivoting the trough into
Southwest. Meanwhile, timing and strength of the next low behind
the remnants of Kulap all have slight variations on Sunday.

&&

.AVIATION...
PANC...LIFR conditions to start the morning hours will
occasionally increase to IFR conditions as passing showers scatter
out the lower clouds. Drier air will gradually work its way into
PANC with MVFR conditions expected this afternoon. SE'ly Turnagain
Arm winds are once again anticipated with potential gusts of just
over 15 knots during the mid to late afternoon hours.

&&

.SHORT TERM FORECAST SOUTHCENTRAL ALASKA (Days 1 through 3/Today
through Sunday night)...

An upper level low and high amplitude trough over the southern
Gulf and northeast Pacific will interact with a north-south
oriented stationary front at it continues eastward today. This
will lead to development of a surface low, which will track
northward across the eastern Gulf this afternoon/evening then
inland across the eastern Copper River Basin tonight. There
remains some uncertainty in the exact track of this low and
westward extent of precipitation. The latest forecast shifts
the low and precipitation a bit farther west in the Copper River
Basin, but just inland from Cordova/Valdez.

Meanwhile, short-waves to the north of the upper low center will
lift northward across Southcentral today, with continued showers
for much of the region. Showers will diminish this afternoon and
evening as a very weak short-wave ridge moves in and low level
flow shifts around to northerly in response to the low in the
eastern Gulf. Expect locally gusty winds along the coast tonight
through early Saturday in response to passage of the low, namely
for Seward/Resurrection Bay, Whittier/Passage Canal, and western
Prince William Sound.

As one trough exits into Canada on Saturday, the next one will
quickly move in from the Bering Sea along with the leading
front ahead of what is currently a hurricane force storm system
in the western Bering Sea. The occluded front will be quite weak
as it reaches Kodiak Island and the western Gulf, but the upper
trough will head right for Southcentral, with rain overspreading
most of the region Saturday night. A series of short-waves will
move through in quick succession, resulting in periods of rain
all the way through Sunday night.

&&

.SHORT TERM FORECAST SOUTHWEST ALASKA (Days 1 through 3: Today
through Sunday night)...

A cool, calm start to the day is underway across Southwest.
Temperatures overnight have fallen well into the 30s across
portions of Bristol Bay where clear skies and calm winds overnight
have allowed healthy radiational cooling of the surface. Nuisance
fog and low stratus has formed in patches where temperatures have
cooled enough for air near ground level to reach saturation, but
it should steadily erode as the day progresses and as temperatures
warm with pockets of sunshine.

Looking towards tonight, a frontal boundary associated with the
massive low associated with the post-tropical remnants of Typhoon
Kulap will reach the coast, pushing a band of rain into the coast
and then farther inland across Bristol Bay and the Kuskokwim Delta
later on Saturday. Fortunately, this front will be rapidly
weakening as it arrives, and southeast winds ahead of the front
will struggle to make it higher than 25 mph for a brief period as
the front reaches the Kuskokwim Delta Coast early on Saturday.
Periods of rain will continue after the front moves inland and
weakens as the large Bering low makes progress towards Bristol Bay
as it fills and weakens.

There is some remaining uncertainty regarding the track of the
Bering low by the time we get into Sunday, as a new system moves
along the Aleutians out west and begins to impact the trajectory
of the original system moving across the eastern Bering. If the
low takes a more north track, there is some potential for higher
than normal water levels with high tides between Sunday and Sunday
night as onshore flow potentially picks up near Bristol Bay and
the Kuskokwim Delta Coast. However, this scenario appears less
likely at this time, and a weaker system with a more south track
towards Bristol Bay is still anticipated. In any case, wet and
rainy conditions will persist near the low through Sunday night,
particularly over Bristol Bay.

&&

.SHORT TERM FORECAST BERING SEA/ALEUTIANS (Days 1 through 3:
Today through Sunday night)...

The Hurricane force remnant low associated with former Typhoon
Kulap is roaring into the southwest corner of the Bering Sea this
morning. Estimated surface wind gusts near 80 mph have recently
been reported at the surface south of the low from Shemya this
morning. A recent and well-positioned scatterometer pass supports
a swath of at least 65 knot sustained winds just to the north,
encompassed by an enormous storm force wind field beginning to
push into the western Bering and along the far western Aleutian
Chain. The good news is this low is reaching it's maturing phase
based on satellite observations, and the entire wind field and
associated high seas will slowly but steadily come down as the low
weakens and as the center drifts east into the Bering during the
course of the next couple of days. Hurricane force winds north of
Shemya should diminish to storm force by this afternoon, and the
storm force winds south of the center should drop down to all
gales on Saturday as the low shifts closer to the Pribilofs. In
addition, the low's occluded front will push very quickly east
across the central/eastern Aleutian Chain and Pribilofs through
this evening, sending across a quick-hitting round of gale force
winds and rain as it moves past. A High Wind Warning also remains
in effect for the western Aleutians through this afternoon, with
gusts up to 90 mph remaining possible before the low pulls far
enough away for winds to diminish below warning levels later
today.

Looking into Sunday, uncertainty increases somewhat for the
eventual fate of Kulap's remnants, as another more compact low
begins to track west along the western Aleutians with gusty south
to southwest winds up to gale force and rain showers. This low
should eventually absorb what's left of the remnant low as the
original center pivots towards the northern Alaska Peninsula and
Bristol Bay area. Despite some differences in terms of how this
interaction plays out, the result for the Aleutians will probably
be about the same through Sunday night, with gusty 25 to 35 kt
winds likely persisting out of the west through Sunday night.

&&

.LONG TERM FORECAST (Days 4 through 7: Monday through Thursday)...

A ridge of high pressure provides a brief break of drier weather
and seasonable temperatures over Southcentral Alaska early next
week. Beyond Wednesday, a steady stream of moisture ahead of a
Gulf low pushes northward with a return of cool, cloudy, rainy
conditions for the north Gulf coasts. Out west, a storm system,
albeit weaker, moves into the central Bering Sea on Monday. A
large portion of the Bering Sea and Aleutians could see gusty
winds and rain with this system. The low will then move into the
North Pacific by Tuesday and continues to weaken as it does so. A
stronger low moves through extreme eastern Russia late next week.
Unsettled weather continues as the low and front enters the
Bering/Chukchi Sea. However, models diverge significantly in the
specific details towards the end of the period, but high winds are
a potential for areas along western Alaska.

&&
.AFC WATCHES/WARNINGS/ADVISORIES...
PUBLIC...High Wind Warning: 191.
MARINE...Hurricane Force: 178 411.
         Storm: 177 185 412 413.
         Gale: 170 173-176 179 414.
FIRE WEATHER...NONE.

&&

SYNOPSIS AND MODEL DISCUSSION...BL
SOUTHCENTRAL ALASKA...SB
SOUTHWEST ALASKA/BERING SEA/ALEUTIANS...AS
LONG TERM...MF

SPECIAL WEATHER STATEMENT
National Weather Service ANCHORAGE AK
240 PM AKDT Fri Sep 30 2022

AKZ155-011300-
Kuskokwim Delta-
Including the cities of Bethel and Nunivak Island
240 PM AKDT Fri Sep 30 2022

The remnants of former Typhoon Kulap are pushing across the Bering
and weakening quickly as they move towards Southwest Alaska. This
low will bring high surf conditions to the mouth of the Kuskokwim
and areas northwest Saturday night through Sunday night. The
biggest impact will be at high tide when water levels could reach
2 to 3 feet above the normal high tide line with high surf on top
of that. There is the potential for coastal erosion due to the
high surf.