Small Craft Advisory 409, NWS Juneau, AK

Southeast Alaska Forecast Discussion
National Weather Service Juneau AK
232 PM AKDT Thu Aug 24 2017

.SHORT TERM.../through Saturday night/ An occluded front over the
eastern gulf will move across SE AK tonight and Fri morning.
Another occluded front will move E into the eastern gulf Fri then
across SE AK Fri night. Parent low of both fronts is over the far
western gulf and will wobble around the western half of the gulf
through Sat, then head NE and weaken Sat night along the N gulf
coast. Blended in 12z GFS with previous forecast through 09z Sat
to increase winds a bit ahead of both fronts.

Precip will occur much of the time through Sat night. Rain with
first occluded front will reach the outer coast late this
afternoon, then spread inland this evening. After this front
moves through, precip will become showery. However, next front
will bring more organized rain to the area especially the S half
Fri afternoon and evening. While the rain with both fronts could
be locally heavy at times, not expecting any flooding problems
with streams or rivers as they have emptied out quite nicely from
the early week deluge. Precip should transition back to showers
after second front moves through late Fri night. Onshore flow will
keep showers going over much of the area Sat into Sat night.

Gale force winds are occurring ahead of the first front over the
NE gulf, with 25-30 kt winds over the SE gulf. As the front moves
onshore tonight, winds over the gulf coastal waters should drop to
15-20 kt. They will pick up again Fri afternoon to SCA levels as
second front moves in, then drop back to 15-20 kt later Fri night
and Sat after front moves onshore. Inner channel winds will mostly
remain below SCA levels, but Clarence Strait is expected to reach
25-30 kt tonight, then after a lull Fri morning, pick up to 25 kt
again late Fri afternoon and evening. Elsewhere, other than near
Cape Decision, winds should peak in the 15-20 kt range for the
inner channels. N Lynn Canal may be close to SCA levels at times
especially after the fronts pass through, and a more favorable
pressure gradient orientation develops.

.LONG TERM.../Sunday through Thursday as of 10 pm Wednesday/The
extended forecast remains wet and fall-like for southeast Alaska.
Showers diminish through Monday as a surface ridge of high
pressure builds over the Panhandle behind the front. The central
Panhandle will likely be the driest region especially later
Sunday, with a second wave of precipitation passing over the
southern Panhandle on Sunday. Between late Monday and Tuesday
another low pressure system and its associated weather begin to
affect the southeast Alaska. There is still a fair amount of
uncertainty with the track of the low and exact onset timing of
precipitation; however, once it begins, rainy conditions will
persist through Thursday. Small craft level winds over the Gulf
are expected with this system currently.

Most adjustments to the extended forecast were made between
Sunday and Monday, adding the possibility of some breaks in
precipitation. Sunday was handled with an ECMWF and GFS blend.
WPC was the primary input beyond that timeframe due to large
discrepancies with the track of the next low. The ECMWF is
currently keeping the low pressure center much further west, while
the GFS places the low center much further east. Forecast
confidence is lower beyond the weekend.

&&

.AJK Watches/Warnings/Advisories...
PUBLIC...None.
MARINE...Gale Warning for PKZ043-051-052.
     Small Craft Advisory for PKZ036-041-042.

&&

RWT/PRB

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