Small Craft Advisory 616, NWS Anchorage, AK

Southcentral and Southwest Alaska Forecast Discussion
National Weather Service Anchorage AK
423 AM AKDT Sat Aug 11 2018

.ANALYSIS AND UPPER LEVELS...
The pattern over the region is an active one with multiple
features moving through. One is a fast moving wave that is pushing
through Southcentral Alaska bringing rain to the area. Behind this
system is a deepening low south of the central Aleutians that is
developing from the remnants of Typhoon Shanshan. It is
intensifying as it has gained jet support and is being ushered
toward the Bering. A weaker upper level low is further west over
the western Aleutians bringing light rain to the islands.

&&

.MODEL DISCUSSION...
Overall the models are handling the synoptic features well through
the mid term. There are some discrepancies with the low tracking
into the Bering Saturday night with the EC being slightly faster
than the other solutions, but this would result in minimal
differences in impacts. The bigger struggle for the models are the
weak waves in the upper level flow between the low over
Southcentral Alaska and the low south of the central Aleutians.
These differences cause a challenge with timing of rain in between
the two main features over southern Alaska today.

&&

.AVIATION...
PANC...Winds will diminish through the morning then remain light
through the remainder of the TAF period. However, there will be
Turnagain Arm winds out of a southeast direction around 35 kt
this morning. The Turnagain Arm winds will diminish through the
day and at this time do not look to bend in over the airport. VFR
conditions will persist through the day before deteriorating this
evening as a front moves in from the south. MVFR conditions will
then last through the night.

&&

.SHORT TERM FORECAST SOUTHCENTRAL ALASKA (Days 1 and 2)...
One upper level short-wave over Southcentral will exit to the
east this morning bringing a brief break in rain to some areas
later this morning through the afternoon hours. An atmospheric
river will transport a series of upper waves embedded in a
tropical-like environment, with very warm and moist air spreading
northward toward Southcentral. Rain will spread back across Kodiak
Island this morning, the Kenai Peninsula and Prince William Sound
this afternoon, and the remainder of Southcentral this evening
through the overnight hours.

Meanwhile, amplification of the upstream pattern will lead to
rapid intensification of a low over the north central Pacific
today. This low will bottom out over the eastern Bering before
beginning to weaken as it continues to Southwest Alaska on Sunday.
A north-south oriented front extending from this low will march
eastward across the Gulf Sunday through Sunday night, bringing
strong winds and heavy rain to much of the region. The heaviest
rain will fall along the Gulf coast and western Susitna Valley,
while strong low level southeasterly flow will keep the Western
Kenai Peninsula, Anchorage, and the Matanuska Valley drier. While
winds will be strong and widespread, do not think this will be a
case of damaging winds. Both the low center and surface front will
be in a weakening state as they impact Southcentral. Also, a look
at forecast soundings indicates a weakly unstable boundary layer,
conducive to vertical mixing of winds, but not mountain wave
activity. Still, with wet soils and fully-leaved trees, winds
could be strong enough in the Anchorage area to produce some
isolated downed branches or trees.

&&

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

A low centered southwest of Nunivak Island continues to weaken
this morning as its associated occluded front decays over
southwest Alaska. Southwest flow aloft will keep clouds and
showers across the southwest mainland through Saturday evening. A
second, much stronger system will begin to impact the area
Saturday night, as a rapidly deepening low moves into the eastern
Bering from the north Pacific. Winds and precipitation will
increase Saturday night into Sunday morning as the low moves
toward the southwest coast Sunday afternoon. The front will
quickly traverse the area during the day Sunday with the low
moving onshore by Sunday evening. A slight risk of thunderstorms
is possible ahead of the front Sunday afternoon in the middle
Kuskokwim basin. Gusty southerly winds ranging from 40 to 55 mph
ahead of the low will shift to the northwest Sunday evening and
persist through Monday evening. Areas of coastal erosion and minor
coastal flooding are possible, especially from Cape Newenham to
Goodnews Bay and from Port Heiden to Pilot Point, Sunday evening
and Monday evening as water levels peak at one to three feet above
high astronomical tide.

&&

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

The main focus through the forecast period is the development and
rapid deepening of a strong low moving northeast into the area
Saturday and Sunday. The first band of precipitation out ahead of
the low will continue to move across the eastern Aleutians and
Alaska Peninsula this morning. Additional precipitation will
advance toward the eastern Aleutians later today as a warm front
tracks north. Gale and storm-force winds will develop tonight both
ahead of the low and behind the low as it rapidly intensifies and
moves into the Bering west of Dutch Harbor. Colder air advecting
in from the north behind the low will produce gusts of 55 to 65
mph from the central Bering and Pribilofs south through the
central and eastern Aleutians. These winds will continue through
Sunday before slowly diminishing from west to east as the low
moves onshore late Sunday. Gusty northerly winds will continue
across the the eastern Bering and portions of the eastern
Aleutians and Alaska Peninsula through Monday. Farther west, high
pressure will settle over the western Bering and Aleutians. This
will keep winds light, but low clouds and areas of fog should
remain in place through Monday as a result of the stable airmass.

&&

.LONG TERM FORECAST (Days 3 through 7: Sunday night through
Friday)...
The extended forecast beginning Sunday night remains in an active
wet pattern across the southern mainland and eastern Bering as low
pressure centers over the Kuskokwim. A cloudy pattern with drier
conditions is expected to the west across much of the central and
western Bering as a ridge builds from the North Pacific. Low pressure
over the Southwest fills as it takes a slow southeasterly track
to the Gulf Monday through Thursday. Rain should be considerably
less organized by Tuesday afternoon across the southern mainland
with the low center moving to the northeast Gulf waters.

For Wednesday through Friday, isolated to scattered chances for
rain remain across the region as short waves move about a broad
trough along the mainland. During this timeframe for the Bering,
another storm system is expected to track from west to east. Model
uncertainty increases considerably for the second part of the
week, especially in regards to this next storm system. The main
struggle for models is that a strong short wave dives south across
the eastern Bering on Wednesday and they differ in how they handle
this energy with the approaching storm from the west. A blend of
the operational models and their ensembles brings increasing chances
of rain from west to east across the Bering.

&&

.AFC WATCHES/WARNINGS/ADVISORIES...
PUBLIC...None.
MARINE...Gales...130 131 132 136 137 138 139 150 160 165 170 171
				 173 174 175 176 179 180 181 185 352 412 413 414.
		 Storms...155 172.

&&

SYNOPSIS AND MODEL DISCUSSION...DK
SOUTHCENTRAL ALASKA...SEB
SOUTHWEST ALASKA/BERING SEA/ALEUTIANS...TM
LONG TERM...KH

SPECIAL WEATHER STATEMENT
National Weather Service ANCHORAGE AK
1219 PM AKDT Sat Aug 11 2018

AKZ101-111-121-125-131-135-141-145-171-121230-
Anchorage-Matanuska Valley-Western Kenai Peninsula-
Western Prince William Sound-Northeast Prince William Sound-
Southeast Prince William Sound-Copper River Basin-Susitna Valley-
Kodiak Island-
Including the cities of Anchorage, Eagle River, Indian, Eklutna,
Palmer, Wasilla, Sutton, Chickaloon, Kenai, Soldotna, Homer,
Cooper Landing, Whittier, Seward, Girdwood, Moose Pass, Valdez,
Thompson Pass, Cordova, Glennallen, Eureka, McCarthy, Paxson,
Slana, Talkeetna, Willow, Cantwell, and Kodiak City
1219 PM AKDT Sat Aug 11 2018

...Rain and Strong Winds in store for Southcentral Alaska Sunday
into Monday...

Areas of strong winds and heavy rain will move through Southcentral
Alaska Sunday through Monday as the remnants of former-typhoon
Shanshan move into the region.

The system will impact Kodiak Island early Sunday morning first
and move up Cook Inlet and into the inland areas by Sunday
afternoon. The Cook Inlet and Susitna Valley areas will likely see
both rain and gusty winds Sunday afternoon into early Monday
morning as the pattern is favorable for both to occur
simultaneously.

The strongest winds are expected to be in Turnagain Arm and along
the Copper River with gusts of 50 mph or greater likely in these
areas. However, gusty winds around 40 mph are also possible in
parts of the Anchorage area and near the Knik River Valley.

The rain will also bring rises to the rivers and streams across
the region. The area of greatest concern is in the Susitna Valley
with the streams coming out of the Talkeetna Mountains such as
Willow Creek and Montana Creek. These area streams will likely
approach bankfull conditions by Sunday night and continue into
Monday or Tuesday.

In addition, an unnamed lake restricted by Bear Glacier in Kenai
Fjords National Park near Seward AK continues to release water.
Water levels in Bear Glacier Lagoon are high and expected to
remain high through Sunday morning. Iceberg production and
movement is also expected. Persons traveling or recreating in the
area are urged to remain alert for rising water levels, potential
flooding, and iceberg movement over the next few days.

Keep up with the latest weather forecasts and information on
flooding potential at: www.weather.gov/afc

SPECIAL WEATHER STATEMENT
National Weather Service ANCHORAGE AK
1223 PM AKDT Sat Aug 11 2018

AKZ155-161-121230-
Kuskokwim Delta-Bristol Bay-
Including the cities of Bethel, Hooper Bay, Nunivak Island,
King Salmon, Dillingham, Naknek, and Pilot Point
1223 PM AKDT Sat Aug 11 2018

...HIGH SURF AND COASTAL EROSION POSSIBLE ALONG KUSKOKWIM BAY AND
BRISTOL BAY COASTS SUNDAY NIGHT THROUGH MONDAY NIGHT...

High surf and coastal erosion is possible along the Kuskokwim Bay
and Bristol Bay coastlines starting Sunday night through Monday
night.

A strong storm system from the remnants of former-typhoon Shanshan
is currently moving over the eastern Aleutians and will track
into Southwest mainland Alaska Sunday evening. As the system
tracks inland, High-end gale-force winds are expected to develop
along the back end of the system which will bring high surf and a
small storm surge to Kuskokwim and Bristol Bays beginning Sunday
night and persisting into Monday night.

The storm surge is expected to reach up to 2 ft above the
grassline and high surf will break on top of this surge. This
brings the potential for erosion on some beaches.

Persons with property near the shore should take precautions to
move it farther away from the water if possible.

Keep up with the latest weather forecasts at: www.weather.gov/afc