Gale Warning 516, NWS Anchorage, AK

Southcentral and Southwest Alaska Forecast Discussion
National Weather Service Anchorage AK
454 AM AKDT Wed Sep 14 2022

.ANALYSIS AND UPPER LEVELS...

On satellite imagery there is a low over mainland Alaska with a
remnant frontal boundary and a low over the Western Bering. The
longwave pattern features a deep trough axis over Southcentral and
the Gulf Of Alaska. There is a jet core of 80 knots east of Cold
Bay and a second jet core north of Attu Island with an estimated
magnitude of 100 knots. On radar there is light precipitation
over portions of Southwest Alaska, Southcentral Alaska and the
Gulf Of Alaska. Also on satellite imagery although distant this
morning, there are multiple tropical systems in the West Pacific
Basin. The one of concern is Typhoon Merbok. Merbok will impact
the Aleutians and other parts of Alaska later this week.

&&

.MODEL DISCUSSION...

Models are in decent agreement through the next 24 hrs. Then model
divergence emerges in the Northwest Pacific regarding the
intensity and the timing of Merbok's extra-tropical transition.
The global models all have a major low pushing across the Bering
followed by Merbok becoming extratropical later this week and
moving into the Bering. As newer model data becomes available
anticipate updates to the forecast.

&&

.AVIATION...
PANC...The Kenai Radar (PAHG) continues to ping onto light
precipitation over northern Cook Inlet and Knik Arm this morning.
Cigs will dip below 5,000 feet at times and light showers are
possible at times. The potential for fog near or at PANC are
actively being monitored and amendments will be made as needed.

&&

.SHORT TERM FORECAST SOUTHCENTRAL ALASKA (Days 1 through
2: Today through Fri morning)...

The longwave trough will continue to sit over the region today.
An upper level low has formed near the northern Alaskan Range.
While a weak shortwave extends across the Susitna valley. These
two features will produce showers today from the Susitna valley
southward toward the Mat valley and Anchorage area as well as the
western Kenai Peninsula. Tonight into Thursday a transitory ridge
will move across the area. This will allow for some sunny breaks
this afternoon and sunshine through at least mid-day Thursday. By
Thursday afternoon and evening a shortwave will bring more rain
from the Susitna valley and southwards towards Anchorage extending
into the Kenai Peninsula. The shortwave will move across
Southcentral Wednesday night and Thursday morning spreading the
rain eastward. Winds along Turnagain Arm and the Copper River
Basin will increase Thursday as the pressure gradient tightens up.
The Knik valley winds will also increase on Thursday.

&&

.SHORT TERM FORECAST SOUTHWEST ALASKA (Days 1 through 3: Today
through Saturday morning)...

The last remnants of low that was nearly stationary over
Southwest for the past two days is moving south over over the
Aleutian Range and into the Western Gulf. A few remnant showers
exist over Southern Bristol Bay and the northwest slopes of the
Kilbuck Mountains, but otherwise most of the region is clear of
precipitation. However, fog and low stratus blanket most of the
region and will continue to do so for the rest of the day today.

Rain will return as a rapidly strengthening storm moves east along
~61N latitude today and tomorrow. The system's front will reach
the coast this evening, bringing another round of rain and
southerly to southwesterly winds through the night. A few
shortwaves streaming east with the jet stream, to the south of
the low, will also help to enhance rainfall rates over Bristol
Bay through Thursday evening, while the rest of the region returns
to a more showery regime. The influence from this system will
wane overnight Thursday, but the next storm will be right on it's
tail.

A very strong low pressure system, which will become the extra-
tropical remnants of Typhoon Merbok, will send it's front into
Southwest Alaska Friday morning. The rain will be heavy, but
overall not long lasting as the front moves through. The main
impact to the region, particularly the Kuskokwim Delta, will be
strong winds and elevated surf/storm surge. The current forecast
is for winds of 50 to 65 mph along the coast with gusts to 75 mph
possible. Farther inland areas like Bethel could also receive
winds in the 45 to 60 mph range. Winds will peak in the overnight
hours and slowly subside through the day on Saturday. Storm surge
guidance indicates some areas could receive surge between 3 and 6
ft above normal highest tide line. Stay tuned as we dial in the
details over the coming days.

&&

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

A weak and elongated area of low pressure will move east along the
Aleutian Chain today, bringing small craft westerlies and rain. To
the north, a rapidly intensifying low is forming quickly over
Russian waters, which will move east towards St. Matthew Island as
a storm force low through today. Focus then shifts to what will be
the extra-tropical remnants of Typhoon Merbok, which will cross
the Aleutian Chain as a Hurricane Force low between Shemya and
Amchitka. For now the core of the strongest winds appears to be
over the widely uninhabited Rat Islands, however there still
remains some uncertainty in the exact low track and how it will
interact with a shortwave moving west out of Kamchatka.
Regardless, gusts upwards of 75 mph are still possible/expected
over the populated islands as well. As the low moves north over
the Chain it will continue to deepen, bottoming out somewhere
between 935 and 945 mb Friday morning. It will then deviate it's
northerly track to the east, which will bring the Pribilof
Islands into the southern edge of the strong wind corridor to the
southeast of the low center. A High Wind Watch is now in effect
for the Pribilof Islands from Friday morning through Friday night
for southwest winds 50 to 65 mph with gusts up to 85 mph possible.
As the storm continues its northeasterly trajectory towards St.
Lawrence Island on Saturday, winds will slowly diminish over the
central Bering.

&&

.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 195 187-191.
MARINE...Storm 411 412 177 178 185. Gale 413 414 175 176 181.

&&

SYNOPSIS AND MODEL DISCUSSION...PJS
SOUTHCENTRAL ALASKA...RLC
SOUTHWEST ALASKA/BERING SEA/ALEUTIANS...CJ
MARINE/LONG TERM...CL