High Surf in Alaska, October 24 to 27, 2016

Northern Alaska Forecast Discussion
National Weather Service Fairbanks AK
210 PM AKDT SUN OCT 23 2016

Aloft...
The current long wave pattern consists of a ridge over mainland
Alaska with deep trough over the Sea of Okhotsk and the NW
Pacific. Several strong short wave troughs will move northeast
through this flow causing the long wave trough deepen and move
east into the Bering Sea on Mon and Tue creating a very high
amplitude pattern with very strong dynamics centered over the
Bering sea from Mon through next weekend.

The first strong short wave that now lies from the NW Bering to
the SE Bering will move to Anadyr to the Se Bering to the Yukon
Delta by 4am Mon and the over NW Alaska Mon where it will weaken.
This is supporting a strong surface frontal system with rain, snow
and strong winds which will be mentioned below in the surface
features.

A second trailing short wave over the southern Bering Sea will to
Cape Navarin to the southeast Bering by 4am Mon...and then merge
with the first short wave along a Point Hope to Anvik line by 4pm
Mon. There will be scattered rain and snow showers between the
first short wave and this trailing short wave which will taper off
late Mon as the short waves move into the ridge and weaken.

A third and much stronger short wave which now extends south from
Kamchatka will move to lie north south across the western Bering
Sea by 4pm Mon...to Cape Navarin to the central Aleutians by 4am
Tue...to Provideniya to the Yukon Delta by 4pm Tue...to Wrangel
Island to Kotzebue to McGrath by 4am Wed...and then move NE and
weaken. This will support a strong rapidly deepening surface low
on Mon and a strong occluded front which will contain very strong
winds and rain. The surface systems will be addressed below.

Surface...
A 1030 mb high over the Eastern Interior of Alaska will retreat
east in the Yukon Territory Mon and then weaken slowly. This will
keep conditions generally clear and cooler than normal over
the Eastern Interior into Tue with east winds developing in areas
prone to easterly drainage widns such as Delta Junction.

A 974 mb low in the NW Bering Sea will move nw and weaken by Mon.
An occluded front associated with this low that lies from Cape
Navarin to the SE Bering Sea will move to Provideniya to Nunivak
Island by 4am Mon...to Cape Lisburne to Kotzebue to Anvik and
weakening by 4pm Mon...and then moving NE and dissipating.
Expect mainly rain with this front diminishing Mon as the front
moves NE and weakens. expect SE winds 20-30kt along and just ahead
of this front. The precipitations could start as snow along the
coast and inland. Will see scattered to isolated rain showers
southwest of the front over the water.

A low developing in the southwest Bering Sea will be a 970 mb low
by 4am Mon...a 952 mb low in the far western Bering by 4pm Mon...a
949 mb 300 nm southwest of Cape Navarin by 4am Tue...a 951 mb low
150 nm west of Anadyr at 4pm Tue...then weakening slowly through
Wed. An occluded front extending southeast from this low will move
to 100 nm west of Cape Navarin to the western Aleutians by 4pm
Tue...to Anadyr to the Pribilofs by 4am Tue...to Wrangel Island to
the Bering Strait to the Yukon Delta by 4pm Tue...and then
weakening along a Cape Lisburne to McGrath line by 4am Wed. Expect
southerly Storm force winds with this front Mon and Mon night
decreasing to Gales Tue. Winds of 50 mph gusting to 70 mph are
expected from Late Mon through early Tue over zone 213...while
south winds of 40 mph gusting to 50 mph for about 8 hours are
expected Tue in Zones 214 and 211. Also expect widespread rain
with the front.

These winds will likely cause coastal flooding in zone 213
starting late Mon.

&&

.DISCUSSION...
Models initialize well and in fair agreement on both large and
small scale features through 4pm Tue. GFS deepens the next low
moving north over the western Bering Sea more rapidly and keeps it
a bit further West on Tue than the other models. At this time
prefer the GFS solution as by Monday there is an extremely dynamic
environment devloping in the western Bering and most of dynamic
energy is moving north and probably more quickly than forecast due
to the high energy present.

Start to see more difference on timing and strength of short
waves by Wed, and from Thu on see significant differences on the
timing, location and strength of short waves and other details,
although the highly dynamic long wave pattern is similar on all
models through next weekend. For this reason will still use GFS
for Wed and then lean more more towards ensembles for location
and timing of features from Thu on...but will keep very strong
strength of features as associated strong winds as shown by
individual model solutions.

Coastal Hazard Potential Days 3 and 4...
Expect storm surge 3 to 4 ft Mon night through Tue over St
Lawrence Island and the Bering Strait. This will cause high surf
and minor coastal flooding Mon night through Tue night.

Expect storm surge of 3-4 feet Tue over the Yukon Delta and the
Seward Peninsula from Nome west. This is expected to cause high
surf and may cause minor coastal flooding Tue. Flooding impacts
should not be major as the duration of 30kt or greater winds is
less than 12 hrs for these areas. We will issue a Coastal Flood
Watch for zones 214 and 211 for Tue. This may be downgraded to a
high surf advisory as we get closer to the time of occurrence.

There is the potential for another strong storm causing coastal
flooding in these same areas Thu and Fri but still too much
uncertainty in model location of the storm centers and wind
directions at this point in time to assess probability of it
occuring.

&&

.AFG WATCHES/WARNINGS/ADVISORIES...
High Wind Watch for AKZ213.

Coastal Flood Watch for AKZ211-AKZ213-AKZ214.

Small Craft Advisory for PKZ200-PKZ215-PKZ220-PKZ230.

Gale Warning for PKZ210-PKZ225.
&&

JB OCT 16