Small Craft Advisory 640, NWS Anchorage, AK

637 
FZAK52 PAFC 152231
CWFALU

Coastal Waters Forecast
National Weather Service Anchorage Alaska
231 PM AKDT Sun Aug 15 2021

Coastal Waters Forecast for Southwest Alaska+Bristol Bay+The
Alaska Peninsula Waters and the Aleutian Islands up to 100 nm out.

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.

PKZ199-161130-
231 PM AKDT Sun Aug 15 2021
.SYNOPSIS FOR SOUTHWEST ALASKA+BRISTOL BAY+THE ALASKA
PENINSULA WATERS AND THE ALEUTIAN ISLANDS...

A 999 mb low 330 nm south of Adak strengthens to 995 mb 85 nm 
south of Seguam Island Mon morning. The low shifts to 50 nm east of 
Chignik and weakens to 1005 mb Tues afternoon. Its front crosses the 
Aleutian Islands and spreads into Bristol Bay through Tues 
afternoon. A series of weak lows cross the northern Bering through 
Tues afternoon.

$$

PKZ150-161130-
South of the AK Peninsula Sitkinak to Castle Cape-
231 PM AKDT Sun Aug 15 2021

...SMALL CRAFT ADVISORY MONDAY AND MONDAY NIGHT...

.TONIGHT...W wind 20 kt. Seas 6 ft.
.MON...SW wind 20 kt becoming S 30 kt in the afternoon. Seas 8 ft.
Rain.
.MON NIGHT...S wind 30 kt becoming W 25 kt after midnight. Seas 11 
ft.
.TUE...W wind 25 kt. Seas 9 ft.
.TUE NIGHT...W wind 15 kt. Seas 8 ft.
.WED THROUGH FRI...W wind 15 kt. Seas 7 ft.

$$

PKZ155-161130-
South of the AK Peninsula Castle Cape to Cape Sarichef-
231 PM AKDT Sun Aug 15 2021

...SMALL CRAFT ADVISORY MONDAY AND MONDAY NIGHT...

.TONIGHT...W wind 15 kt becoming S 20 kt after midnight. Seas 5 ft.
.MON...SE wind 30 kt. Seas 9 ft. Rain.
.MON NIGHT...SW wind 25 kt. Seas 9 ft.
.TUE...SW wind 20 kt. Seas 9 ft.
.TUE NIGHT...Variable wind 10 kt. Seas 9 ft.
.WED THROUGH THU...SW wind 15 kt. Seas 7 ft.
.FRI...NW wind 15 kt. Seas 5 ft.

$$

PKZ160-161130-
Bristol Bay-
231 PM AKDT Sun Aug 15 2021

.TONIGHT...W wind 20 kt. Seas 4 ft.
.MON...SW wind 10 kt becoming SE in the afternoon. Seas 3 ft.
.MON NIGHT...E wind 15 kt becoming NE after midnight. Seas 3 ft.
.TUE...N wind 10 kt. Seas 2 ft.
.TUE NIGHT...W wind 15 kt. Seas 2 ft.
.WED...SW wind 10 kt. Seas 2 ft.
.THU...SW wind 15 kt. Seas 3 ft.
.FRI...NW wind 15 kt. Seas 3 ft.

$$

PKZ165-161130-
Port Heiden to Cape Sarichef-
231 PM AKDT Sun Aug 15 2021

...SMALL CRAFT ADVISORY MONDAY...

.TONIGHT...W wind 15 kt becoming S 20 kt after midnight. Seas 5 ft.
.MON...SE wind 25 kt. Seas 5 ft. Rain.
.MON NIGHT...E wind 15 kt. Seas 4 ft.
.TUE AND TUE NIGHT...Variable wind 10 kt. Seas 3 ft.
.WED...SW wind 15 kt. Seas 2 ft.
.THU...SW wind 20 kt. Seas 4 ft.
.FRI...NW wind 15 kt. Seas 4 ft.

$$

PKZ170-161130-
Cape Sarichef to Nikolski Bering Side-
231 PM AKDT Sun Aug 15 2021

...SMALL CRAFT ADVISORY THROUGH MONDAY...

.TONIGHT...SE wind 25 kt. Seas 5 ft.
.MON...SE wind 30 kt. Seas 6 ft. Rain.
.MON NIGHT...E wind 15 kt. Seas 5 ft.
.TUE...N wind 15 kt. Seas 5 ft.
.TUE NIGHT...Variable wind 10 kt. Seas 3 ft.
.WED THROUGH THU...W wind 15 kt. Seas 4 ft.
.FRI...N wind 15 kt. Seas 4 ft.

$$

PKZ171-161130-
Unalaska Bay-
231 PM AKDT Sun Aug 15 2021

...SMALL CRAFT ADVISORY MONDAY...

.TONIGHT...SE wind 20 kt. Seas 3 ft. Rain.
.MON...SE wind 25 kt. Seas 3 ft. Rain.
.MON NIGHT...Variable wind less than 10 kt. Seas 2 ft. Rain.
.TUE AND TUE NIGHT...N wind 10 kt. Seas 2 ft.
.WED...N wind 10 kt. Seas 2 ft.
.THU...SW wind 10 kt. Seas 3 ft.
.FRI...N wind 10 kt. Seas 3 ft.

$$

PKZ172-161130-
Cape Sarichef to Nikolski Pacific Side-
231 PM AKDT Sun Aug 15 2021

...SMALL CRAFT ADVISORY THROUGH MONDAY NIGHT...

.TONIGHT...SE wind 25 kt. Seas 7 ft. Rain.
.MON...SE wind 25 kt becoming S in the afternoon. Seas 9 ft.
.MON NIGHT...S wind 20 kt. Seas 10 ft.
.TUE...NW wind 15 kt. Seas 10 ft.
.TUE NIGHT...Variable wind 10 kt. Seas 8 ft.
.WED...NW wind 15 kt. Seas 6 ft.
.THU...W wind 15 kt. Seas 6 ft.
.FRI...Variable wind 10 kt. Seas 5 ft.

$$

PKZ173-161130-
Nikolski to Seguam Island Bering Side-
231 PM AKDT Sun Aug 15 2021

...SMALL CRAFT ADVISORY THROUGH MONDAY NIGHT...

.TONIGHT...SE wind 25 kt. Seas 6 ft. Rain.
.MON...E wind 25 kt. Seas 7 ft. Rain.
.MON NIGHT...NE wind 20 kt. Seas 8 ft.
.TUE...N wind 15 kt. Seas 7 ft.
.TUE NIGHT...Variable wind 10 kt. Seas 5 ft.
.WED THROUGH THU...W wind 15 kt. Seas 4 ft.
.FRI...Variable wind 10 kt. Seas 4 ft.

$$

PKZ174-161130-
Nikolski to Seguam Island Pacific Side-
231 PM AKDT Sun Aug 15 2021

...SMALL CRAFT ADVISORY THROUGH MONDAY NIGHT...

.TONIGHT...SE wind 20 kt in the evening becoming E 25 kt. Seas 8 ft.
Rain.
.MON...SE wind 25 kt becoming S in the afternoon. Seas 11 ft.
.MON NIGHT...S wind 20 kt in the evening becoming variable 10 kt.
Seas 11 ft.
.TUE...N wind 15 kt. Seas 9 ft.
.TUE NIGHT...Variable wind 10 kt. Seas 6 ft.
.WED...N wind 15 kt. Seas 6 ft.
.THU...W wind 15 kt. Seas 6 ft.
.FRI...NW wind 15 kt. Seas 5 ft.

$$

PKZ175-161130-
Seguam Island to Adak Bering Side-
231 PM AKDT Sun Aug 15 2021

...SMALL CRAFT ADVISORY MONDAY AND MONDAY NIGHT...

.TONIGHT...E wind 20 kt. Seas 5 ft.
.MON...NE wind 25 kt. Seas 7 ft.
.MON NIGHT...N wind 25 kt. Seas 8 ft.
.TUE...N wind 15 kt. Seas 6 ft.
.TUE NIGHT...Variable wind 10 kt. Seas 3 ft.
.WED THROUGH THU...W wind 15 kt. Seas 4 ft.
.FRI...SW wind 15 kt. Seas 4 ft.

$$

PKZ176-161130-
Seguam Island to Adak Pacific Side-
231 PM AKDT Sun Aug 15 2021

...SMALL CRAFT ADVISORY THROUGH MONDAY NIGHT...

.TONIGHT...SE wind 15 kt becoming NE 25 kt after midnight. Seas 7 
ft. Rain.
.MON...NE wind 25 kt. Seas 10 ft.
.MON NIGHT...NW wind 25 kt. Seas 10 ft.
.TUE...N wind 20 kt. Seas 7 ft.
.TUE NIGHT...Variable wind 10 kt. Seas 6 ft.
.WED THROUGH FRI...W wind 15 kt. Seas 6 ft.

$$

PKZ177-161130-
Adak to Kiska-
231 PM AKDT Sun Aug 15 2021

...SMALL CRAFT ADVISORY THROUGH MONDAY NIGHT...

.TONIGHT...NE wind 25 kt. Seas 6 ft.
.MON...N wind 30 kt. Seas 7 ft.
.MON NIGHT...N wind 25 kt. Seas 7 ft.
.TUE AND TUE NIGHT...W wind 15 kt. Seas 5 ft.
.WED THROUGH THU...W wind 15 kt. Seas 5 ft.
.FRI...SW wind 20 kt. Seas 5 ft.

$$

PKZ178-161130-
Kiska to Attu-
231 PM AKDT Sun Aug 15 2021

...SMALL CRAFT ADVISORY TONIGHT...

.TONIGHT...N wind 25 kt. Seas 6 ft.
.MON...NW wind 20 kt. Seas 5 ft.
.MON NIGHT...NW wind 15 kt. Seas 4 ft.
.TUE...W wind 15 kt. Seas 5 ft.
.TUE NIGHT...W wind 20 kt. Seas 5 ft.
.WED...SW wind 15 kt. Seas 5 ft.
.THU THROUGH FRI...S wind 20 kt. Seas 6 ft.

$$

PKZ179-161130-
Pribilof Islands Near Shore Waters-
231 PM AKDT Sun Aug 15 2021

.TONIGHT...SW wind 20 kt becoming S 15 kt after midnight. Seas 6 ft.
.MON...E wind 15 kt. Seas 5 ft.
.MON NIGHT...NE wind 10 kt. Seas 4 ft.
.TUE...Variable wind 10 kt. Seas 5 ft.
.TUE NIGHT...SW wind 15 kt. Seas 4 ft.
.WED...SW wind 20 kt. Seas 4 ft.
.THU...NW wind 15 kt. Seas 5 ft.
.FRI...Variable wind 10 kt. Seas 4 ft.

$$

PKZ180-161130-
Kuskokwim Delta and Etolin Strait-
231 PM AKDT Sun Aug 15 2021

...SMALL CRAFT ADVISORY TONIGHT...

.TONIGHT...SW wind 25 kt. Seas 7 ft.
.MON...S wind 20 kt. Seas 6 ft.
.MON NIGHT...SE wind 15 kt becoming NE after midnight. Seas 4 ft.
.TUE...NW wind 10 kt. Seas 3 ft.
.TUE NIGHT...W wind 10 kt. Seas 2 ft.
.WED...SW wind 25 kt. Seas 4 ft.
.THU...W wind 20 kt. Seas 4 ft.
.FRI...NW wind 15 kt. Seas 4 ft.

$$

PKZ181-161130-
North and West of Nunivak Island-
231 PM AKDT Sun Aug 15 2021

...SMALL CRAFT ADVISORY THROUGH MONDAY...

.TONIGHT...SW wind 25 kt. Seas 8 ft.
.MON...SW wind 25 kt diminishing to 15 kt in the afternoon. Seas 7 
ft.
.MON NIGHT...SW wind 15 kt in the evening becoming NW. Seas 4 ft.
.TUE...NE wind 15 kt. Seas 4 ft.
.TUE NIGHT...E wind 15 kt. Seas 3 ft.
.WED...S wind 25 kt. Seas 7 ft.
.THU THROUGH FRI...W wind 20 kt. Seas 4 ft.

$$

PKZ185-161130-
Saint Matthew Island Waters-
231 PM AKDT Sun Aug 15 2021

...SMALL CRAFT ADVISORY TONIGHT...

.TONIGHT...SW wind 25 kt. Seas 8 ft.
.MON...E of St Matthew island, SW wind 20 kt. W of St Matthew Island,
N wind 15 kt. Seas 6 ft.
.MON NIGHT...NE wind 15 kt. Seas 5 ft.
.TUE...E wind 20 kt. Seas 4 ft.
.TUE NIGHT...S wind 25 kt. Seas 6 ft.
.WED...NW wind 25 kt. Seas 8 ft.
.THU...W wind 20 kt. Seas 6 ft.
.FRI...S wind 20 kt. Seas 5 ft.

$$

Southcentral and Southwest Alaska Forecast Discussion
National Weather Service Anchorage AK
448 PM AKDT Sat Aug 14 2021

.ANALYSIS AND UPPER LEVELS...
There is split flow over Alaska this morning, with the subtropical
jet nearly zonal across the North Pacific and a weak polar jet
driving short-waves out of the Russian Arctic and toward mainland
Alaska. A short-wave trough over Southcentral Alaska is tracking
slowly eastward, with weak low level instability in place (as per
the 12Z Anchorage sounding). This is leading to showers from
Anchorage, the Matanuska Valley, and interior Kenai Peninsula
eastward across Prince William Sound and the Copper River Basin.
A weak vertically stacked low has formed over the northern Gulf
and is beginning to re-focus a lot of the vertical motion southward
over the Gulf, with weakening forcing over Southcentral as we
head through the day.

Upstream, a weaker and disorganized short-wave is pushing onshore
along the Kuskokwim Delta. There is an extensive cloud shield
covering the northern Bering Sea and headed inland across
Southwest Alaska. However, rainfall with the short-wave is light
and focused across the Kuskokwim Delta.

In the southern stream, a weak vertically stacked low is spinning
south of the Aleutian chain. A new low is just beginning to form
to the south along the subtropical jet. This will ultimately
become the next storm system of interest for the Aleutians and
into the Gulf/Southcentral. For the moment, weak ridging across
the southern Bering Sea, Aleutians, and Alaska Peninsula is
leading to benign conditions. In fact, satellite imagery shows
quite a bit of sunshine out there with some localized areas of
low clouds and fog.

&&

.MODEL DISCUSSION...
Model guidance is in general agreement with large scale features
and the evolution of the pattern over the next few days. There are
minor differences in individual short-waves transiting both the
northern and southern stream flow as well as potential interaction
of energy from the two streams Monday night/Tuesday. This will
affect the details of timing of rain/wind, especially with the
triple point low forming and moving across the northern Gulf on
Tuesday. However, overall confidence in the trends within the
forecast is high.

&&

.AVIATION...
PANC...VFR conditions and light winds will persist.

&&

.SHORT TERM FORECAST SOUTHCENTRAL ALASKA (Days 1 through 3:
Saturday night through Tuesday)...

An upper level trough currently over Southcentral AK is providing
enough instability to keep cloud cover and rain showers forming
over the region today. This trough will shift east overnight and
exit our forecast area. Behind it, weak ridging moves in tomorrow
which will briefly provide a break in the weather. However,
abundant moisture in the area from recent rains means plenty of
cloud cover will still develop even with ridging in place.

This ridge is just transient in nature and is already on its way
out Monday night. Behind it, another weak shortwave dropping down
from the Interior will move into Southcentral late Monday into
Tuesday. There is some question in model guidance with how far
south this trough digs, so some adjustment may be needed in the
forecast the next couple of days. We do know that it will provide
another round of rain shower for Southcentral. It's just a
question of how many showers we'll get and where. Stay tuned.

&&

.SHORT TERM FORECAST SOUTHWEST ALASKA (Days 1 to 3: Tonight
through Tuesday)...

Westerly flow on the southern periphery of a longwave trough
centered over northern Alaska and the Chukchi Sea will continue
over the next several days. A series of shortwave perturbations
will track across the Y-K Delta and Kuskokwim Valley area within
this corridor of nearly steady west to southwest winds, each
bringing some potential for rain showers as they move inland. The
first of these waves will continue to track across from the Y-K
Delta to interior Bristol Bay this evening, with a band of showers
moving with it from northwest to southeast. A few areas of fog
may form as the line of showers clears out with the added low
level moisture, mainly over the Y-K Delta and up against the
Alaska Range through tomorrow morning.

The next more pronounced shortwave in the series will move inland
near Norton Sound by Monday morning, with an associated surface
low moving inland over the Seward Peninsula by around the same
time. A slow moving front will trail behind the low into northern
portions of the Y-K Delta, but it appears increasingly likely it
will stall out north of the forecast area prior to shearing out by
Monday night. Thus, rainfall chances have been kept low for this
forecast package, except for where upslope enhancement will be
strongest near the Kuskokwim Mountains and western Alaska Range.
Yet another round of moderate rainfall will work up along the
AKPen into Bristol Bay on Tuesday as a front and developing
triple point low move towards the Gulf.

&&

.SHORT TERM FORECAST BERING SEA/ALEUTIANS (Days 1 to 3: tonight
through Tuesday)...

The pattern over particularly southern portions of the outlook
area will become somewhat more active at the start of the new week
as a low and front progress across the Aleutians and AKPen through
Tuesday. A broad zone of mainly westerly winds up to small craft
strength will continue for much of this period farther north
across the northern Bering. These winds will die off behind
another front that will move inland over the Y-K Delta by Monday
morning, with a new low moving off of Kamchatka then bringing
increasing southeast winds and rain west of St Matthew Island by
Tuesday.

The weather story will be more active and complex along the
Aleutians and southern Bering, especially between Monday and
Tuesday. A nearly stacked low will continue to spread easterly
winds and a few showers along mainly the Western Aleutians through
Sunday, gradually spreading into the southern Bering through
Sunday night. Meanwhile, a separate low and shortwave aloft moving
out of the North Pacific will begin to merge with the
aforementioned low sitting to the northwest near the Western
Aleutians. The associated phasing and merge of the two features
aloft will help the resulting single surface low to deepen to
around 995 mb by Monday morning.

A front will then track swiftly northeast from Monday to early
Tuesday along the Eastern Aleutians and AKPen ahead of the low,
bringing a brief period of southeast winds and moderate rainfall
as it moves across. The strongest winds will be likely through
gaps and passes on Monday, with gusts likely peaking in the gale
force range before the front and a developing triple point low
race quickly into the Gulf by Tuesday morning. Things will begin
to settle down by Tuesday as the then occluded in weakening low
slowly fills over the Eastern Aleutians.

&&

.MARINE (Days 3 through 5: Wednesday through Friday)...

A low over the AKPen will cross into the Gulf on Tuesday. A gale force
barrier jet will likely set up along the north Gulf Coast Tuesday
afternoon before weakening Tuesday night. Otherwise, winds will
remain less the gale force through the period.

&&

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

Ensemble and deterministic model agreement is moderate to high in
the long term. A stout ridge over the northeastern Pacific will
nudge north into the Gulf Wednesday while a broad, longwave trough
remains over the Bering Sea. Mostly zonal flow will exist over
the interior. This pattern will place the AOR in a fairly
progressive weather pattern that begins with widespread light rain
Wednesday through Friday, before drying out slightly over the
weekend. A series of shortwaves are expected to follow the primary
upper level low track from the Gulf of Anadyr, over the southern
Mainland, and into Southeast Alaska. As the waves interact with
the north Pacific ridge they will pick up moisture, warm air, and
upper level energy to bring rain throughout the region. Thursday
looks to be the wettest day in the long term as two shortwaves
merge over Southwest Alaska, placing the southern mainland in a
broad region of southwest flow with strong upper level dynamics.
As the low complex moves east Friday, a shortwave ridge should
bring drier, and clearer weather to the region for the start of
the weekend.

&&

.AFC WATCHES/WARNINGS/ADVISORIES...
PUBLIC...NONE.
MARINE...NONE.
FIRE WEATHER...NONE.

&&

SYNOPSIS AND MODEL DISCUSSION...SB/CQ
SOUTHCENTRAL ALASKA...BB
SOUTHWEST ALASKA/BERING SEA/ALEUTIANS...AS
MARINE/LONG TERM...CJ