Small Craft Advisory 761, NWS Anchorage, AK

Southcentral and Southwest Alaska Forecast Discussion
National Weather Service Anchorage AK
526 AM AKDT Wed Sep 28 2022

.ANALYSIS AND UPPER LEVELS...

The Rossby Wave pattern remains amplified. An upper level low over
Bristol Bay continues to move northeastward. Upper level ridging
currently extends across Southeast Alaska through the Copper
Basin.

Closer to the surface, radar imagery shows rain and showers moving
northward across the Gulf of Alaska to over Cook Inlet, the Kenai
Peninsula and Prince William Sound. Another area of rain continues
to move northward across Bristol Bay to over Southwest Alaska.

&&

.MODEL DISCUSSION...

Models are in fair agreement with respect to the placement and
intensity of synoptic scale features. There are some slight
differences in position with respect to the next Bering Sea low.
However, there is high confidence the track of this next system
will remain much farther south of the track Merbok took. This
southerly track of this next system will allow for offshore wind
flow across Southwest Alaska which will minimize the risk for
coastal flooding. Models have also trended towards a deeper low
comparing the 12z runs with the 00z runs.

&&

.AVIATION...
PANC...VFR conditions will persist for this TAF period with
temporary MVFR conditions inside areas of light rain before 16z.
Low-level wind shear is expected through 29th/12z as winds will be
significantly stronger aloft than near the surface.

&&

.SHORT TERM FORECAST SOUTHCENTRAL ALASKA (Days 1 through 3...Wed
through Fri)...The well-advertised frontal system will move
through the area today. This will bring rain and winds to just
about all locations through the end of the week. Rain has already
started from Kodiak up through Seward. It will continue to track
northeast through the day reaching the Prince William Sound and
Cordova by this afternoon. The heaviest rain will certainly be
focused along the coast with steady onshore flow. The highest
totals will target the Whittier and Portage areas with 3-4" likely
by Thu evening. Seward will also see an extended period of wet
weather. However, easterly flow at the mountain top level near
the coast will limit their overall totals. We still expect around
2.5" for Seward by Thu evening. For many inland population centers
(Anchorage, Palmer, Kenai), cross barrier flow will lead to
mostly dry conditions until Thu.

Winds will be the other impactful part of this storm. The gradient
will tighten through the day allowing for a steady increase of
southeast winds. This gradient will favor places like the
Turnagain and Knik Arms, as well as the Copper River Basin. Some
of the strongest winds of the season thus far are also expected
this evening along the Anchorage Hillside. The upper levels will
become more favorable for gusty winds later today as a weak upper
level jet moves right over the Chugach mountains. Gusts to 55 mph
will be possible this evening. Please see the Special Weather
Statement for more details. Marine areas will see winds reach
storm force through the Barren Islands. As the front lifts north
tonight, it will compress in the barrier jet region along the
north Gulf coast. Gusts to at least 50 kt are expected in this
area as well.

By Thu, winds will subside significantly. As the upper level
energy from the low center itself starts to work through Cook
Inlet, expect chances for rain to increase for inland areas. While
the rainfall amounts do not look particularly heavy, it will
continue the pattern of cloudy and wet as we head towards the end
of September.

&&

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

The most inclement conditions associated with a front working
across the Alaska Peninsula (AKPen) should peak early this
morning, at least when it comes to the very gusty gap winds
ongoing over Bristol Bay in particular. Winds currently gusting
upwards of 40 mph between Iliamna and Koliganek should gradually
subside through this evening as the front falls apart and the
parent low begins to shift inland near the Kuskokwim Mountains
this evening. Unfortunately, the reprieve from drenching rainfall
will not come so early. The entire low will essentially stall out
as it elongates along the Southwest coast, keeping overcast and
showery conditions in play through at least Thursday evening. At
the same time, northwest winds supported by persistent cold air
advection and a tight southwest to northeast pressure gradient
will begin to creep up towards the coast and along the northern
AKPen on Thursday morning. Northwesterly gusts of 20 to 30 mph
(and perhaps a bit higher for southern Bristol Bay) will be
possible with these winds along the coast Thursday morning, but
should diminish as the day progresses. In addition, expect shower
activity to decrease in coverage by Thursday night as the low
finally pulls away and into the western Gulf.

Looking towards Friday, the limited impacts from what's currently
Typhoon Kulap should begin to be felt over Southwest. The (by
then fully extratropical) low's weakening, occluded frontal
system will approach the Southwest coast with modestly increasing
southeast winds and rain beginning by late Friday night.
Fortunately, the massive low over the Bering itself is still not
expected to reach Southwest, and the recovery efforts in the wake
of Merbok are not expected to be especially disrupted by this
second storm system.

&&

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

In the near term, the immediate attention across the region will
initially be focused on the corridor of gusty, gale force winds
currently pushing across the central Aleutians and Bering. These
winds are occurring west of a large upper low lumbering slowing
northeast near Bristol Bay. A finger of seasonably cool low level
temperatures continues to push into the Bering west of the low,
and this cold air advection is helping to support the gusts into
or near gale force along central and eastern portions of the
Aleutian Chain, as well as up over the Pribilofs. These gusty
northwest winds should persist along the southern Alaska Peninsula
(AKPen) and eastern Aleutians for the next day or so as the low
nearly stalls out over Southwest. However, winds should diminish
late in the day Thursday as the low continues to fill and
eventually drift towards the Gulf.

Attention shifts quickly from there to an extremely intense storm
system expected to take shape over the western Bering and
Aleutians between Thursday and Friday. By Thursday morning, the
current tropical cyclone moving over the Northwest Pacific,
Typhoon Kulap, will complete its transition into an intensely
powerful extratropical low. This low is expected to interact
favorably with a separate upper trough moving west out of
Kamchatka, with the core of the then non-tropical low is expected
to phase strongly with this second upper feature during the
morning on Thursday. At the surface, this dynamic interaction
should foster rapid deepening of the system's surface low, perhaps
reaching peak intensity between 940 and 950 mb early Thursday
morning as it enters the southwestern Bering. Southeast winds
along the low's leading frontal structure will increase to high
end storm force across the western Aleutians by midday Thursday,
with gusts well into Hurricane force expected. Winds will flip to
westerly after a short lull as descending, cool air wraps into the
south side of the low as is continues past Shemya. Peak gusts
with this second blast of winds could approach 80 to 90 kts (or
around 100 mph) over Shemya and Attu late Thursday night into
early Friday morning. The High Wind Watch for the western
Aleutians has been upgraded to a High Wind Warning with this
package now that confidence for the very strong winds has greatly
increased.

Looking into Friday, the entire low will begin to stall out and
weaken as it's occluded front wraps around the center multiple
times and as the system becomes vertically stacked. What will
briefly be a Hurricane force low should weaken back to storm force
as it slows to a crawl west of the Pribilofs. This should
thankfully keep most of the wind field out over water for most of
the day on Friday, with the strongest winds in gale force range
mainly continuing to impact the central/western Aleutian Chain
through Friday evening.

&&

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

Looking ahead in the extended forecast, the latest operational
model runs are in a decent agreement, but begin to diverge in the
specific details towards the end of the period. The main feature
heading into the weekend will be a deep area of low pressure
moving through Bering Sea from remnants of Kulap. This system
continues to bring strong winds and moderate to heavy rain along
and ahead of the front across the Aleutian Chain, Pribilof
Islands, and Southwest Alaska. By Sunday, the low turns southeast
and weakens as it tracks towards the Alaska Peninsula. Another
storm system, albeit weaker, approaches the central and western
Aleutians with the next round of wind and rain for early next
week. Unsettled weather continues into Tuesday as a North Pacific
low lifts toward the Kamchatka Peninsula. However, models diverge
significantly in the low placement and strength. Meanwhile, a
transient ridge of high pressure provides a brief break of drier
weather early Saturday over Southcentral. The aforementioned
Bering front will then shift into the northern gulf and then into
the southern mainland for a return of cool, cloudy, and rainy
conditions.

&&
.AFC WATCHES/WARNINGS/ADVISORIES...
PUBLIC...High Wind Warning 191.
MARINE...Storm Warning 130 177 178.
Gale Warning 119 120 125 131 132 136 137 138 141 155 160
165 170 171 172 179 180 181 185 351 352 414.
FIRE WEATHER...NONE.

&&

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