Small Craft Advisory 638, NWS Juneau, AK

Southeast Alaska Forecast Discussion
National Weather Service Juneau AK
420 PM AKDT MON OCT 17 2016

.SHORT TERM...A low pressure trof over the eastern gulf will
drift onshore tonight. Another trof will move into the eastern
gulf Tue. A developing low will move NE into the SW gulf by late
Tue. Models were in general agreement on the main features and
close to previous forecast, so did not make any significant
changes to the pressures/winds especially over the gulf.

Main forecast concerns will be precip potential, TSTM potential,
and winds. A fairly organized band of showers is over the far eastern
gulf and much of the panhandle this afternoon, and will continue
moving NE across the area tonight. The southern area has only a
few showers right now, but they will see more showers move in late
tonight as second trof approaches the area. The NE gulf coast will
see shower activity diminish overnight tonight as shortwave
ridging moves in aloft...and Tue will likely see scattered showers
at most in that area. The far N panhandle should see any snow
change to rain by late this afternoon in the lower elevations as
S-SE low level flow increases, so will allow the winter weather
advy for zones 18 and 19 to expire at 4 pm.

Best threat for TSTMS will be along the trofs moving in and mainly
over the water. Think bulk of TSTMS will be done with first trof
by time evening forecast goes out so will not mention in new
forecast for this evening. Late tonight and Tue though, second
trof will have some TSTM potential over the far SE gulf along axis
of greatest instability. Some of these may reach the far southern
coast before they dissipate by late Tue afternoon with trof moving
onshore.

Strongest winds tonight will be over the inner channels with 15-25
KT S-SE winds ahead of the first trof. These winds will diminish
slowly tonight. They may pick up some on Tue with second trof but
think they will remain below SCA levels. Will have generally
15-25 KT winds over the E gulf with strongest winds along and
ahead of the trofs. Over the far SW outer waters, 25-30 KT SE
winds will move in late Tue afternoon in response to approaching
low and occluded front. Marine zone 52 will also see winds pick up
to around 25 KT late in the day.

.LONG TERM...A gale force front will move across the eastern gulf
Tuesday night. Expect E-SE winds along the outer coast to
increase through the night with gusts of 35-45mph continuing
through Wednesday morning. Most inner channels will increase to
small craft level with this front and some, like Cross Sound and
Clarence Strait to gale force. Rain will be moderate as it moves
through on Wednesday then transition to showers behind the main
front. Have continued with a slight chance of thunderstorms over
the gulf.

Main change to the forecast was adjusting position of a low
center that develops along the Tue night/Wed front. 12z models
came into better agreement on this feature today, so used a blend
of the NAM/ECMWF/GFS. Models differ more and more with each day
of the extended forecast on the timing/placement of troughs moving
through, but they all agree that it will be an active weather
week, especially compared to the first half of the month.

&&

.AJK Watches/Warnings/Advisories...
PUBLIC...None.
MARINE...Small Craft Advisory for PKZ031-033-034-036-052.
     Small Craft Advisory due to Seas for PKZ022-041>043-051.
&&

RWT/Ferrin

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