Gale Warning 531, NWS Anchorage, AK

Southcentral and Southwest Alaska Forecast Discussion
National Weather Service Anchorage AK
447 PM AKDT Sat Oct 12 2019

.ANALYSIS AND UPPER LEVELS...
Skies have cleared across much of the southern Mainland as broad
offshore flow develops in the wake of a southeast retreating low
over the eastern Gulf. Strongest gap flows to 35 kt were evident
across the northern and western Gulf. Satellite imagery shows a
developing low and associated front over the North Pacific heading
north toward the Alaska Peninsula. Satellite imagery also shows a
fairly disorganized surface low southwest of the Pribilof
islands.

&&

.MODEL DISCUSSION...
The Models overall have a similar broad synoptic handling of
surface features, particularity the remnants of Hagibis, through
Monday morning. The Canadian NH becomes a significant outlier as
it drops the remnants of Hagibis south of the Aleutians Tuesday,
while the remainder of the model suites move it north. Otherwise,
will lean toward the GFS with this feature (Hagibis) for
consistency.

&&

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

&&

.SHORT TERM FORECAST SOUTHCENTRAL ALASKA (Days 1 and 2)...

Northwest flow aloft and offshore flow at the low levels along the
coast is supporting the stunning fall afternoon that has enveloped
the region. Offshore flow weakens tonight as high pressure takes
over, thus expect much cooler temps tonight as inversions develop
with clear skies.

A front will move into the Southern Gulf of Alaska bringing gales
and rain to Kodiak by Sun night and Monday, but high pressure and
clear skies continue to dominate into early next week.

&&

.SHORT TERM FORECAST SOUTHWEST ALASKA (Days 1 and 2...Sun and Mon)...
A rather benign weather pattern will persist for the end of the
weekend and start of the week. A weak area of high pressure will
move through the area tonight into Sun keeping the area dry and
mostly clear. We can't rule out some patchy fog Sun AM, especially
along river valleys. During the day Sun, a North Pacific low will
slide closer to Kodiak Island as it strengthens. The net effect
for much of SW AK will be an increase in offshore/NE winds. These
winds will reinforce the dry conditions as they pull air from the
Interior portions of AK. The Alaska Peninsula will be clipped by
this system as it pivots through the area. Winds will reach into
the 20-30 mph range along the peninsula with the best chances for
rain on the southern side late Sun afternoon and evening.

A much stronger system will be pushing through the Bering on Mon.
It will start to brush up against the West coast by Mon afternoon
bringing a sharp switch to gusty south-southeast winds. Clouds
will be on the increase through the day as well with rain moving
in by the evening timeframe.

&&

.SHORT TERM FORECAST BERING SEA/ALEUTIANS (Days 1 and 2...Sun and
Mon)...
The remnants of Typhoon Hagibis continue to be the big story for
the Bering and Aleutians as we move into the early part of the
week. First, there is one weak low bringing some showers to the
Eastern Aleutians and the Pribilof Islands this evening. This
feature will merge with a developing North Pacific system heading
into Sun. This will keep light rain falling from Dutch Harbor to Sand
Point through most of Sun before the system pulls away into the
Gulf of AK Sun night.

The forecast envelope is starting to narrow for the track and
strength of Hagibis as we move into Sun night and Mon. The biggest
change to this forecast package is to shift the low slightly to
the north as the models continue to develop a consensus. As it
makes the extra-tropical transition, it will tap into some cold
air over Siberia on Mon. This will allow the surface pressure to
drop into the mid 950 mb range Mon morning. The surface pressure
gradient will tighten up during this time and allow for some
hurricane-force winds to wrap around the western side of the low.
These winds look to primarily impact the marine areas and hold to
the north of the Aleutian Chain. However, there will still be a
chance of some localized hurricane-force gusts for the Central
Aleutians to include Atka and Adak. There will be plenty of rain
associated with this storm as well. With strong upper level
support and some low level cold air advection, the system will be
able to maintain its intensity for quite some time. It will slowly
track to the north-northeast and allow for the waves to continue
to build into Tue. We have increased the peak wave heights by
about 5 ft early Tue morning with this forecast package. Please
see the Marine Weather Statement and the Coastal Waters Forecast
for more details on this storm.

&&

.MARINE (Days 3 through 5)...

Bering Sea/Aleutians: Post-tropical cyclone Hagibis will begin to
fill and exit to the northern Bering Tuesday. Thus, while storm
force winds will initially be widespread in the Bering (with a
broad swath of gales elsewhere), winds will diminish during the
day. While models have come into better agreement with the track
of former Hagibis, there is still a lot of uncertainty with what
comes after. The main theme is that either a short wave or a
closed low will develop near the western Aleutians late Tuesday.
This feature will track eastward across the Bering just north of
the Aleutians late Tuesday into Wednesday. Increased winds are
expected, but the strength will depend on whether a closed low
forms... so for now, the range of possibilities span from low end
gales to storm force winds. As the cold air mass behind the
associated front moves across the warmer SSTs of the Bering,
instability will increase, thus isolated thunderstorms look
possible over the southern Bering Sea Wednesday. Winds will
diminish Thursday and general cyclonic flow will prevail in the
Bering.

Gulf of Alaska: Easterly winds in the northern Gulf will diminish
Monday into Tuesday. The forecast in the Gulf becomes murky by
Wednesday. General low pressure is expected with winds mostly
below advisory level... however small craft advisory level swell-
driven seas will likely persist. Late Wednesday, an upper low
will cross the AKPEN then redevelop a surface low in the Gulf
early Thursday. High uncertainty continues with this setup, but
assuming this low comes to fruition, expect increased winds and
precipitation in the periphery of the low.

&&

.LONG TERM FORECAST (Days 3 through 7)...

The excitement in the long term continues to be focused in the
Bering Sea and Aleutians. As post-tropical cyclone Hagibis exits
to the northern Bering Tuesday, focus turns to what happens in its
wake. Model consistency remains poor, but the general theme is
that either a short wave or a deeper closed low will develop in
the baroclinic zone under a 160 to 170kt jet. It will traverse the
southern Bering (just north of the Aleutians) from west to east
and likely bring a brief return of gales to the Aleutians/
southern Bering. Isolated thunderstorms are possible behind the
associated front Wednesday as modified Arctic air flows over
relatively warm water.

Meanwhile, due to the track of the former typhoon, impacts over
the Southwest mainland look minimal. As the system shifts
northward, it will push a cold front across the Aleutians into the
west coast in the rough Tuesday to Wednesday time frame.
Precipitation will be possible along the west coast, and increased
southerly winds are expected. However, it's worth noting that the
front will have significantly weakened by the time it reaches the
mainland. Thus, while the Kuskokwim Delta Coast could see gusts
above 40kt, warning level winds are not expected. In the Wednesday
to Thursday timeframe, precipitation in the Bristol Bay area will
be possible as the other low/short wave moves into the coast...
but confidence is poor given the inconsistency in that feature.

Friday into Saturday, longwave troughing will set in from the
central Pacific into the Bering. Expect cloudier weather and
general southerly flow over Southwest. Models indicate shortwaves
will likely rotate around the low bringing periods of unsettled
weather, but it's way too soon to get into timing/location
specifics.

Over Southcentral, generally dry weather is expected through
midweek. High pressure will persist over northern Alaska, and
cold conditions inland with offshore winds will dominate through
midweek. With this scenario, increased winds are likely in the
usual gaps, including Thompson Pass and the Matanuska Valley. A
series of fronts will move from the Gulf northward. This will
potentially bring precipitation to the North Gulf Coast, but
generally expect precipitation to stay over the marine area.
During the later part of the week, the ridge will retrograde to
the north. A wetter, or at least cloudier pattern is possible and
overnight lows won't be quite as cold as earlier in the week.

&&

.AFC WATCHES/WARNINGS/ADVISORIES...
PUBLIC...NONE.
MARINE...Gales...131, 132, 138, 351, 352, 412, 150, 155, 173, 176.
		 Storms...411, 413, 175, 177, 178.
FIRE WEATHER...NONE.

&&

SYNOPSIS AND MODEL DISCUSSION...RMC
SOUTHCENTRAL ALASKA...JA
SOUTHWEST ALASKA/BERING SEA/ALEUTIANS...MSO
MARINE/LONG TERM...MM