Small Craft Advisory 565, NWS Juneau, AK

Southeast Alaska Forecast Discussion
National Weather Service Juneau AK
318 PM AKDT MON SEP 12 2016

.SHORT TERM...Previous forecast remains on track with period of
heavy rain and gusty winds tonight. Impressive rainfall totals in
Yakutat today with hourly rates reaching as high as 0.66 inches.
Between 10 am and 1 pm the Yakutat airport received 1.78 inches of
rain. According to precipitation frequency estimates that happens
once every five years. The atmospheric river that is responsible
for the heavy rain will shift south and east tonight into the
northern and central panhandle. As it does so these areas can
expect a 3-6 hour period of very heavy rainfall. A quick 1-2
inches of rain is expected. The stream of moisture will reach the
southern panhandle late Tuesday morning. Rain chances will remain
high over the northern panhandle on Tuesday with continued onshore
flow and a weak shortwave moving over the area during the
afternoon. However, rainfall will generally be light.

The other big story in the short term will be the wind. Strong low
level flow combined with a tightening pressure gradient will lead
to strong winds developing over the central and northern panhandle
tonight. Southerly gale force winds will also develop over the
inner channels. The strongest winds will be in the Skagway area as
strong 700 mb southwest flow will act to enhance lee side
troughing and the southerly pressure gradient. Additionally, two
shortwaves will move across the area which will provides further
support for high wind gusts up to 60 mph. The high wind watch was
upgraded to a high wind warning through early Tuesday. Gusts up
to 45 mph can be expected for the remainder of the central and
northern panhandle. Winds will gradually diminish Tuesday as the
pressure gradient slackens.

Used hi-res guidance for updates to the previous forecast.

.LONG TERM...Atmospheric river sliding southeast across the region
is forecast to dissipate over the far southern panhandle at the
start of the long term period (Tuesday night). In the wake of the
AR, the surface pressure gradient will remain sufficiently tight
for small craft southerlies over Northern Lynn Canal, with winds
forecast to weaken to 15-20 kt by Wednesday afternoon.

Deep-layer moisture returns to the entire panhandle Wednesday
night, resulting in a rainy period through Thursday night. At the
surface, large spread in MSLP is present in available
deterministic guidance Wednesday and Thursday. Thus, shortwave
surface features were smoothed out of the pressure grids, which
yields persistent southerlies over the gulf in the range of 15-25
kt during much of the long term. Otherwise, model guidance shows a
series of upper distrubances treking across the region from the
weekend through at least the middle of next week, which will
favor periods of rain for SERN AK.

&&

.HYDROLOGY...The burst of heavy rain will lead to steep rises in
area rivers and streams tonight and early Tuesday. A flood watch
has been issued for the Taiya River near Skagway from late tonight
through Tuesday afternoon. See the flood watch statement for
additional information. Other rivers and streams may approach
bankfull, but flooding is not expected at this time.

&&

.AJK Watches/Warnings/Advisories...
PUBLIC...STRONG WIND from 7 PM AKDT this evening through late tonight for
     AKZ025.
     STRONG WIND until 1 AM AKDT Tuesday for AKZ022.
     STRONG WIND from 7 PM this evening to 1 AM AKDT Tuesday for
     AKZ020-021.
     STRONG WIND through late tonight for AKZ019.
     High Wind Warning from 7 PM this evening to 7 AM AKDT Tuesday
     for AKZ018.
     Flood Watch from 10 PM AKDT this evening through Tuesday
     afternoon for AKZ018.
     STRONG WIND until 7 PM AKDT this evening for AKZ018.
     STRONG WIND from Tuesday morning through Tuesday afternoon for
     AKZ018.
     STRONG WIND until 4 PM AKDT this afternoon for AKZ017.
MARINE...Gale Warning for PKZ012-013-021-022-031>034-043-051.
     Small Craft Advisory for PKZ011-035-041-042-052-053.
&&

TPS/Garner

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