Small Craft Advisory 552, NWS Juneau, AK

Southeast Alaska Forecast Discussion
National Weather Service Juneau AK
339 PM AKDT THU SEP 8 2016

.SHORT TERM...WV imagery showed a midlevel shortwave impulse/120+
kt jetstreak located south of the Aleutians Friday afternoon, and
a closed upper low positioned over southwestern interior AK. Both
of these features are forecast to phase over the gulf tonight,
which will contribute to strong surface cyclogenesis. Intense low-
level WAA will subsequently spread NEWD across the panhandle late
tonight, yielding a zone of heavy stratiform rainfall. This WAA
wing will also be accompanied by rapidly strengthening surface
winds, with gusts to 40 mph developing from AKZ022/023 SSE to
AKZ027-028. Model guidance shows the environment becoming
increasingly convective in the wake of the WAA zone, with showers
becoming probable over the gulf and southern/central coastal
areas. A few elevated offshore thunderstorms will also be possible.

By midday Friday, the bulk of 12Z and 18Z deterministic model
guidance shows a 985 mb surface low approaching Cross
Sound...which then moves east-northeast toward a location
immediately north of Juneau by late Friday afternoon. As the low
ejects east, a sting jet is forecast to develop along the southern
periphery of the cyclone over the east-central gulf. This will aid
in the development of storm force westerlies over the central
outer waters during Friday afternoon, and possibly high wind
gusts to 60 mph in Sitka. There is still uncertainty regarding
wind strength at Gustavus and Juneau during Friday afternoon and
evening. The expected track of the surface low could yield
westerly winds gusting to 40 mph...will need to monitor forecast
trends closely during the next 12-24 hours.

Short term forecast updates were generally based off of ECMWF,
NAM, and hi-res NMM guidance. Most changes were local in nature.

.LONG TERM.../ Saturday to Thursday / Weather continues to wind
down after the storm remains have jumped inland to Northern
British Columbia. The ridge is still expected to build over the
gulf later Saturday into Sunday. The ridge axis will then become
positively tilted on Sunday as a short wave and surface feature
starts to move across the northern gulf. This looks to be a
developing atmospheric river that will move east across the
coastal regions passing the Yakutat area Monday, the northern
panhandle Monday night and the southern panhandle Tuesday. Thus
the panhandle only gets about 1 day of drier weather before the
rains return.

Model agreements were fairly solid into the early part of the
week with a minor issue on when the atmospheric river will pass
over the northern gulf. Confidence is above average for the
weekend and first portion of next week. Amount of rains may lead
to some hydro issue Monday to Tuesday for northeast gulf coast
region.

&&

.AVIATION...Heavy rain and gusts to 40 mph will develop over the
central and southern panhandle tonight through Friday...as well as
southerly wind shear from 35-45 kt. Significant westerly wind
gusts to 50 kt are possible at Sitka during mid to late Friday
afternoon.

&&

.MARINE...A strong low pressure system will move across the
central and eastern gulf Thursday night into Friday morning, and
then move inland across the central panhandle Friday afternoon
through Friday evening. Westerly storm force winds are forecast to
develop along the southern portion of the low over the east
central gulf Friday afternoon. Elsewhere, small craft to gale
force winds will be widespread across the remainder of the gulf
and central/southern inner channels. Seas to 20 feet are also
probable over the southern half of the gulf during Friday
afternoon and night.

&&

.HYDROLOGY...Heavy rain is forecast to spread north and east
across the panhandle Thursday night. Storm total rainfall
accumulations from 2 to 5 inches is expected by Friday evening.
This will cause area creeks, streams, and rivers to experience
rising water levels...some possibly to bankful.

&&

.AJK Watches/Warnings/Advisories...
PUBLIC...STRONG WIND from Friday morning through Friday afternoon for
     Akz022.
     STRONG WIND from 1 AM AKDT Friday through Friday afternoon for
     AKZ027.
     STRONG WIND from late tonight through Friday afternoon for
     AKZ022-023.
     High Wind Watch Friday afternoon for AKZ023.
     Areal Flood Advisory from 7 PM this evening to 2 PM AKDT
     Saturday for AKZ018.
     STRONG WIND from late tonight through Friday afternoon for
     AKZ028.
MARINE...Storm Warning for PKZ042-043.
     Gale Warning for PKZ021-022-033>036-041-051-052.
     Small Craft Advisory for PKZ011-013-031-032.
&&

Garner/Bezenek

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