Gale Warning 402, NWS Anchorage, AK

134 
FZAK61 PAFC 041136
OFFAER

Offshore Waters Forecast
National Weather Service Anchorage AK
336 AM AKDT Mon Sep 4 2017

Offshore waters forecast for the Gulf of Alaska West of 144W

Wind forecasts reflect the predominant speed and direction
expected. Sea forecasts represent an average of the highest
one-third of the combined wind wave and swell height.

PKZ399-050130-
336 AM AKDT Mon Sep 4 2017
.SYNOPSIS FOR THE WESTERN GULF OF ALASKA...
A front will remain over the central Gulf through Tue afternoon. A
1001 mb low south of the central Gulf tonight will ride along the
front to 59N 147W at 995 mb by Tue afternoon, then move inland
near 60N 148W Tue evening at 993 mb. 

$$

PKZ351-050130-
Gulf of Alaska Offshore North of 57N and West of 144W-
336 AM AKDT Mon Sep 4 2017

.TODAY...SE wind 10 to 25 kt. Seas 14 ft.
.TONIGHT...SE wind 15 kt. Seas 11 ft.
.TUE...E wind 10 to 20 kt becoming N 15 to 30 kt in the afternoon.
Seas 7 to 11 ft. Rain.
.TUE NIGHT...S wind 15 to 25 kt. Seas 7 to 11 ft.
.WED THROUGH FRI...E wind up to 15 kt. Seas 3 to 8 ft.

$$

PKZ352-050130-
Gulf of Alaska Offshore South of 57N North of 55N and West of
144W-
336 AM AKDT Mon Sep 4 2017

.TODAY...SE wind 15 to 30 kt. Seas 10 to 16 ft. 
.TONIGHT...SE wind 10 to 25 kt. Seas 11 ft.
.TUE...E wind up to 20 kt becoming SW in the afternoon. 
Seas 6 to 9 ft. Rain.
.TUE NIGHT...S wind 10 to 20 kt. Seas 5 to 9 ft.
.WED THROUGH THU...S wind 10 to 20 kt. Seas 4 to 8 ft.
.FRI...W wind 10 kt. Seas 3 to 6 ft.

$$

Southcentral and Southwest Alaska Forecast Discussion
National Weather Service Anchorage AK
407 AM AKDT Sun Sep 3 2017

.ANALYSIS AND UPPER LEVELS...
The strong low south of the Alaska Peninsula around 50N 160W is
now reaching maximum depth in the upper 960s. An associated strong
frontal system is currently lifting north into the western Gulf.
To the east of the big low, ridging is building over the
Southeast Alaska Panhandle, British Columbia, the Yukon Territory
and into interior Alaska. To the west, northerly flow prevails
across the Bering and central Aleutians with clouds from the
leading edge of the next front system beginning to brush the
western Aleutians.

&&

.MODEL DISCUSSION...
The major upcoming forecast challenge continues to be the
possibility of an atmospheric river setting up across the
northern Gulf coast during the first half of the week. While large
scale upper level features such as a strong southerly jet,
support the possibility, models remain uncertain remain uncertain
regarding the surface features, where the heaviest rain will set
up and how long it might last. Currently the GFS and NAM support a
further east solution with a longer break in between the initial
frontal system and when the heavier rain migrates back west, while
the Canadian and European models support more prolonged wet
weather for the northern Gulf coast. Much will depend on the
strength and persistence of the ridge amplifying to the east.

&&

.AVIATION...
PANC...VFR conditions are expected through the next TAF package.
With the northerly gradient continuing to increase as the frontal
system approaches southeasterly Turnagain Arm winds should stay
bent to the south and remain clear of the airport.

&&

.SHORT TERM FORECAST SOUTHCENTRAL ALASKA (Days 1 through 3)...
The focus continues with the developing storm system south of the
Alaska Peninsula and its leading front which heads north across
the Gulf today. The low makes little headway north so the real
weather maker will be the frontal trough which moves well to the
north and east of the surface low. Two main impacts will be wind
and rain. Gale to storm force winds will spread north across the
Gulf today then should weaken tonight as the front makes landfall
along the Gulf coast. Brisk to strong gap flows will also develop
near channeled terrain, such as, Turnagain Arm, Portage Valley,
and the Matanuska Valley. The gap flows should weaken late
tonight/early Monday morning.

The second impact with this system will be rainfall. As the front
heads north it will bring periods of moderate to heavy rainfall to
coastal locals. First impacting Kodiak island today then heading
toward the eastern Kenai and northern Gulf tonight. Although no
flooding is expected for Kodiak there is potential for localized
mudslides along the road system as 2 to 3 inches of rain may fall
before the front passes this evening. Rainfall along the northern
Gulf tonight and Monday will be moderate to potentially heavy at
times. However, there is still uncertainty on the positioning of
upper jet support and accompanying rainfall totals.

&&

.SHORT TERM FORECAST SOUTHWEST ALASKA (Days 1 and 2)...
A mature low pressure system residing south of the Shumagin
Islands will slam a front across the Pacific side of the Alaska
Peninsula through Monday. Moderate to heavy rainfall will be
observed along upslope locations of the Alaska and Aleutian Ranges
while strong cross barrier flow should keep inland areas across
Bristol Bay like King Salmon and Igiugig rather dry. The same
winds that will downslope inland locations will be forced through
several gaps along the Aleutian Range (Lake Clark and Kamishak
Bay) where wind gusts in the 60 to 65 mph range will likely be
observed this afternoon. These winds are expected to diminish late
tonight and Monday as the front weakens and becomes less
favorably oriented. Gusty winds will also be observed across the
Alaska Peninsula where northerly winds coupled with cold air
advection could help squeeze the winds through channeled terrain.
Rainfall will taper off on Monday as the front slides eastward
into the Gulf of Alaska.

&&

.SHORT TERM FORECAST BERING SEA/ALEUTIANS (Days 1 and 2)...
Gale force winds will continue across the eastern Aleutians as a
mature low pressure system south of the Alaska Peninsula continues
to slide eastward. Some cold air advection is helping to squeeze
winds through channeled terrain to create gusty winds but these
are expected to diminish late Monday morning as the low slides
eastward. High pressure is building over the western Bering Sea in
the wake of the low pressure system with a few obs suggesting low
stratus and fog situating underneath the ridge axis. In the
meantime, Tropical Storm 17W (Sanvu) has begun it's extratropical
transition and will be moving near the tip of the Kamchatka
Peninsula early this afternoon. A frontal boundary developing with
the extratropical cyclone will enter the western Bering Sea
before midnight tonight and bring another round of gale force
winds to the Bering Sea. It doesn't appear as if this system will
strengthen as it moves into the Bering Sea with the lack of cold
air over Russia. Rainfall appears to be the biggest concern across
the Aleutians with this system due to the tropical nature of the
air mass.

&&

.LONG TERM FORECAST (Days 3 through 7)...
The low south of the Alaska Peninsula will continue to weaken,
while a secondary low tracks northward through the central Gulf
and into the northern Gulf coast and Prince William Sound area
Tuesday and Tuesday night. Models continue to agree on another
round of precipitation and gusty winds tracking into the northern
Gulf area on Tuesday. However, the models are still struggling
with some timing and strength differences between the GFS & ECMWF
solutions. The GFS, remaining the preferred solution for this
system and very similar to the WPC solution, brings the gusty
winds and rain to the Gulf Coast slightly faster on Tuesday. The
GFS and WPC solutions are also tracking the system further west,
which can result in bringing more rainfall to the interior
portions of Southcentral and the Cook Inlet region. The key
concern remains where the atmospheric river will setup Tuesday
into Wednesday, and which areas will be on the receiving end of a
fair amount of Pacific moisture. Our focus remains over the
southeast Prince William Sound and Cordova areas, where guidance
continues to show moisture streaming northward from the Pacific
and resulting in heavy rainfall over Cordova during the early
part of next week. Therefore, a Flood Watch remains in effect for
the Southeast Prince William Sound area from Monday morning
through late Tuesday night.

Meanwhile, the remnants of Typhoon Sanvu will quickly track
through the central Aleutians Wednesday, then cross into the
northern Pacific and track along the Pacific side of the Eastern
Aleutians and Alaska Peninsula through Thursday. This will bring
widespread gusty winds accompanied by stratus/rain, with the
Bering/Aleutians to be under the influence of strong gusty
northeasterly to northerly winds as it tracks eastward through the
midweek. High pressure will then build in over the western Bering
Thursday night through Saturday.

&&

.AFC WATCHES/WARNINGS/ADVISORIES...
PUBLIC...Flood Watch 135.
MARINE...Storm Warning 119 120 130 131 132 138 150 351 352.
         Gale Warning 125 136 137 139 141 155 160 165 170
                      172 173 174 178 180 414.
FIRE WEATHER...NONE.

&&

SYNOPSIS AND MODEL DISCUSSION...JER
SOUTHCENTRAL ALASKA...BC
SOUTHWEST ALASKA/BERING SEA/ALEUTIANS...MC
LONG TERM...TP