Small Craft Advisory 588, NWS Juneau, AK

Southeast Alaska Forecast Discussion
National Weather Service Juneau AK
343 PM AKDT THU SEP 22 2016

.SHORT TERM...Wet and windy day across the panhandle as a strong
fall front moves through. As of 1 pm the front stretched from Cape
Fairweather SSE just off the outer coast to the western edge of
Haida Gwaii. Winds at Yakutat and buoys 46084 and 46083 flipped to
the W around noon indicating frontal passage at those points. The
front also shows up very well on Biorka Island radar velocity
data as a distinct wind shift. Eastward movement of the front
slowed up a little with the development of a minor wave just west
of Prince of Wales this morning so forecast time of frontal
passage through the panhandle has been pushed back a few hours as
a result. With its current rate of movement the surface front
should reach the Cross Sound and Sitka area by around 4 pm and
progress through the rest of the inner channels through this
evening. Front should exit the panhandle by midnight.

Winds have been gusty today with gusts reaching 35 to 50 mph at
many land areas. Highest gusts as of 1 pm was recorded at Yakutat
with 48 mph this morning. A lot of the wind for the inner channels
stayed aloft as the atmosphere is rather stable so wind gusts did
not reach as high as what could have happened if the atmosphere
was a little more unstable. Marine areas have been even windier
with widespread gales and storm force winds across the gulf before
frontal passage and small craft winds for the northern inner
channels to up to storm force in Clarance Strait. Gusty winds will
continue for the next few hours in the inner channels until
frontal passage. Highest winds will be mainly in the southern
inner channels where strong wind headlines for 40 mph gusts remain
up for the early evening. Post-frontal winds will switch around
to the W in the late evening and diminish to around 10 to 20 mph
and will remain that way through Fri.

Rainfall has been somewhat notable. The northern gulf coast saw
around 2 inches total from the front as some barrier jet effects
reduced rainfall in that area for a few hours. Meanwhile the
northern inner channels have seen a rather steady .15 to .25 inch
per hour rainfall rate since around 10 am. Precip frequency for
that rate is only a 2 year event for most of these areas over a 3
hour period so it is a good wetting rain but it is not something
that would cause flooding. Especially since rivers are low from
the dry weather we had the last few days. The southern panhandle
is just starting to get into the rain and should be raining for
most of the evening. With the front moving through this evening
total rainfall should only amount to 1 to 2 inches for most areas
of the panhandle through tonight. Post- frontal showers will be
the rule for late tonight into Fri. Some rather cool air is
working in behind the front with 500 mb temp reaching -25 C or
colder over the gulf late tonight into tomorrow. This is causing
model LI to reach -2 or less and cape values to reach 200 J/kg
over the gulf. Kept a slight chance of thunder in those areas as a
result.

Short range models were a little fast in bringing the front
through as they did not have the minor wave that formed along it.
Otherwise guidance was rather good. Mainly used some hi-res models
for detail updates today.

.LONG TERM...A showery/convective regime will persist over the
gulf and panhandle through Saturday. The pattern will then change
during Sunday over the SERN gulf/SRN panhandle as an upper ridge
and strong low-level baroclinic zone build NWD. The presence of
the low-level front will provide the antecedent conditions
favorable for surface cyclogenesis. At this time, the strongest
model signal for an intense cyclogenetic event is Sunday night and
Monday as a coupled upper jet structure/upper divergence becomes
collocated with the surface front. However, model spread is large
with regard to the magnitude, track, and speed of the low. Thus,
this part of the forecast will continue to be refined.

After early next week, the primary storm track will generally
emanate from interior AK, which will favor a shower precip mode
mixed with periods of cool/dry continental intrusions. As a
result, a few sea level locations...particularly from Yakutat to
Juneau northward, could experience freezing nighttime lows during
the middle of next week.

&&

.AJK Watches/Warnings/Advisories...
PUBLIC...STRONG WIND until 7 PM AKDT this evening for AKZ026-028.
     STRONG WIND until 4 PM AKDT this afternoon for AKZ024-025-027.
MARINE...Storm Warning for PKZ036.
     Gale Warning for PKZ031-034-035-041.
     Small Craft Advisory for PKZ011>013-021-022-032-033.
     Small Craft Advisory due to Seas for PKZ042-043-051>053.
&&

EAL/Garner

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