Small Craft Advisory 640, NWS Juneau, AK

Southeast Alaska Forecast Discussion
National Weather Service Juneau AK
549 AM AKDT TUE OCT 18 2016

.SHORT TERM...Tuesday and Tuesday night weather looking to be
exciting as showers moving northward across the panhandle with
localized training pattern for shower bands over Baranof and
Chichagof Islands. A trough aloft with moderate vorticity lobe
will spread into the northern panhandle and northeast gulf coast
to renew showers for the afternoon and early evening.

A strong low in the lower to mid 970 mb range south of Kodiak
Island will rotate west to be southeast of Cold Bay by late
Tuesday night. The associated weather front will move into the
southeastern Gulf of Alaska Tuesday night, and a developing wave
on the front will be moving northward along 140 west to the
northern gulf overnight. Expect 40 to 45 kt gale force winds along
and ahead of the front into outer coastal waters. Clarence Strait
will increase up to 35 to 40 kt late tuesday night. Small craft
winds should develop over much of the rest of the marine forecast
area.

.LONG TERM...The gale force front entering the southeast Gulf late
Tuesday night will likely spawn a closed triple point low riding
northward along it. Both ECMWF and the 06Z NAM are indicating
possibly two closed circulations along the front. While the
overall trend the last couple of days has been to edge this or
these waves westward, the fact that the NAM and ECMWF both
maintain some presence toward the east of a tighter circulation
causes enough concern for us to issue a high wind watch for
western Prince of Wales Island and southern Baranof Island for
Wednesday morning. Should winds rise to 50 to 60 miles per hour,
the event duration looks to be around a three to six hour event
and no more as the front and its waves will lift north and west
relatively quickly. Two things working in the event's favor are
the potential of instability with this system as well as a 65 kt
jet at 925 mb. Given this system's passage...moisture will lift
north across the Panhandle and we have raised certainty of rain to
one hundred percent.

The front will leave showers and plenty of instability in its
wake so showers and thunderstorm potential look good. Few changes
were made to the forecast beyond this time frame. Systems will
progress through the gulf into next week offering several bouts of
rain and wind. A cooling trend is possible by next weekend.

NAM initialized the wave development in the far southwest gulf
best on satellite, and we coordinated with ANC to track to the low
following its guidance. Forecast confidence good to average.
Confidence in high wind gusts actually occurring along our coast
is just enough to issue a watch, and given the timing, we felt it
a necessary call.

&&

.AVIATION...Showers moving through the northern half of the
panhandle early this morning are resulting in lower ceilings and
visibilities. There should be a break from 17z to 20z and then
another trough moving across the region this afternoon to early
evening which should impact flight conditions lowering some
locales to marginal levels.

Late tonight the strong weather front moving to the southern
panhandle will increase sustained winds and gusts. Low level wind
shear and turbulence should be expected near rough terrain.

&&

.HYDROLOGY...The overall rainfall numbers are not expected to be
significant in a general pattern like this. Satellite estimates of
the precipitable water is around 0.75" and is 100 to 150 percent
of normal. However, the showers have been organizing themselves
into narrow bands and then training across the same locations and
as a result some locales are getting an inch of rain or more.
Water levels in the streams are low and while they are responding
to the rainfall, flooding is not expected.

&&

.AJK Watches/Warnings/Advisories...
PUBLIC...High Wind Watch Wednesday morning for AKZ023-027.
     STRONG WIND late tonight for AKZ022-023-027.
MARINE...Gale Warning for PKZ036-041>043-051-052.
     Small Craft Advisory for PKZ011-013-021-022-031>035.
     Small Craft Advisory due to Seas for PKZ053.
&&

Bezenek/JWA

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