Small Craft Advisory 563, NWS Juneau, AK

SOUTHEAST ALASKA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE JUNEAU AK
434 PM AKDT THU SEP 22 2011

.SHORT TERM...A RAPIDLY DEVELOPING LOW JUST SOUTH OF THE EASTERN
GULF AS OF EARLY THIS AFTERNOON IS THE FOCUS OF THE SHORT TERM
FORECAST PERIOD. THIS LOW IS FORECAST TO CONTINUE TO RAPIDLY
DEEPEN AS IT APPROACHES THE OUTER COAST NEAR CAPE DECISION EARLY
FRIDAY MORNING. THE UPPER LEVEL CIRCULATION IS BEING WELL
SUPPORTED BY AN OPTIMALLY PLACED JET STREAK UP THROUGH LANDFALL.
BAROCLINIC CLOUD SHIELD WITH A PRONOUNCED COMMA HEAD IS ALREADY
OVER THE SOUTHERN PANHANDLE AND A DEVELOPING DRY SLOT SUPPORTS
CONTINUED DEVELOPMENT AND INTENSIFICATION AS WELL. MORNING MODELS
INDICATING A MINIMUM CENTRAL PRESSURE OF AROUND 965 MB. LOW LEVEL
WIND MAXIMA AT 850 MB ON THE EASTERN SIDE OF THIS LOW FORECAST TO
BE 70 TO 80 KT AND TRACKS OVER PUBLIC ZONES 26, 27, AND 28. FOR
THIS REASON, HAVE EXPANDED THE EXISTING HIGH WIND WARNING TO
INCLUDE ZONE 26, TO INCLUDE THE CITIES OF PETERSBURG, KAKE, AND
WRANGELL. AS THE STORM APPROACHES THE COAST, NORTHERLY WINDS WILL
INCREASE SIGNIFICANTLY OVER SOUTHERN CHATHAM STRAIT AND THE
EASTERN SHORE OF BARANOF ISLAND WILL FEEL THE BRUNT OF THESE
WINDS. HAVE THEREFORE ALSO INCLUDED ZONE 23 IN THE HIGH WIND
WARNING TO COVER THE COMMUNITIES ALONG THE SOUTHEAST COAST OF
BARANOF ISLAND, TO INCLUDE LITTLE PORT WALTER AND PORT ALEXANDER.
HAVE STORM WARNINGS OUT FOR SOUTHERN CHATHAM STRAIT, SUMNER
STRAIT, AND CLARENCE STRAIT. CAPPED WINDS AT A HIGH GALE FOR
STEPHENS PASSAGE AND FREDERICK SOUND, BUT GUSTS OUT OF INTERIOR
PASSES WILL BE EASILY AT STORM FORCE.

 FARTHER NORTH, A SOUTHERLY WIND STILL BLOWS OVER UPPER AND LOWER
LYNN CANAL, BUT THE PRESSURE GRADIENT IS FORECAST TO ABRUPTLY
SHIFT NORTHERLY LATER THIS EVENING WITH THE ZERO ISALLOBAR
BISECTING THE PANHANDLE FROM JUNEAU WEST TO ELFIN COVE AS OF
1 PM. FORECAST NORTHERLY PRESSURE GRADIENT OVER THE CANAL RUNNING
BETWEEN 4 AND 6 DEPENDING ON THE MODEL. GAVE UPPER LYNN CANAL A
MAX GALE FOR LATE TONIGHT INTO EARLY TOMORROW MORNING WITH A
SOLID GALE FOR LOWER LYNN FOR THE SAME TIME FRAME, BUT THIS MAY
BE CONSERVATIVE IF THE ACTUAL PRESSURE GRADIENT WINDS UP BEING
CLOSER TO 6.

 PRECIPITATION ASSOCIATED WITH THIS LOW WILL BE HEAVY AT TIMES,
ESPECIALLY AFTER THE LOW TO MID LEVEL WIND REGIME BECOMES
ONSHORE. CURRENT AMSU IMAGERY IS INDICATING AS MUCH AS
200 PERCENT OF THE NORMAL PRECIPITABLE WATER VALUES. HAVE HEAVY
RAIN OVER LARGE PORTIONS OF THE SOUTHERN HALF OF THE PANHANDLE
THROUGH FRIDAY AFTERNOON.

 MAIN FORECAST CONCERN AND AREA OF GREATEST UNCERTAINTY IN THE
SHORT TERM FORECAST IS THE TIMING OF THE WIND SHIFT AND
ASSOCIATED WIND SPEED INCREASES EXPECTED OVER LYNN CANAL. THE
OTHER AREA OF CONCERN IS THE RESULTING WIND PATTERNS ASSOCIATED
WITH THE LOW ITSELF. THE STORM IS QUITE COMPACT AND, WITH SUCH AN
INTENSE WIND FIELD, MINOR DEPARTURES FROM THE FORECAST TRACK MAY
HAVE SIGNIFICANT IMPACTS ON THE RESULTANT WIND DIRECTIONS. THE
ONE THING THAT SEEMS QUITE CERTAIN IS THAT IT WILL BE EXTREMELY
WINDY LATE TONIGHT AND INTO TOMORROW MORNING.

 USED A BLEND OF ECMWF AND GFS FOR PRESSURE AND WIND. BLENDED GFS
AND NAM FOR POP AND QPF. FORECAST CONFIDENCE IS ABOVE AVERAGE.

.LONG TERM...BY FRI EVENING THE STORM LOW PRESSURE WILL BE
FILLING INTO 980S AND LOSING ITS DEFINITION OVER NORTHERN HALF OF
INNER CHANNELS. SURFACE PRESSURE RISES WILL DRIVE SOUTH WIND ESP
EARLY FRI NIGHT BEFORE SUBSIDING BY SAT MORNING. MAY NEED TO WATCH
LYNN CANAL WIND TO POSSIBLY BECOME BRIEFLY STRONGER FRI NIGHT THAN
THE 25 KT CURRENTLY FCST.

SAT NIGHT AND SUN AN UPPER TROUGH AT 500 MB IS CENTERED OVER THE
EASTERN GULF. WIND ALOFT OVER SE AK WILL BE LIGHT SLY AND
DIFLUENT AS MAIN WIND ENERGY LOOPS AROUND BOTTOM OF TROUGH WELL TO
OUR SOUTH AND INTO PAC NW. ASSOCIATED COOLING ALOFT MAY KEEP
SHOWERS PERSISTING ESP OVER MOUNTAINS BUT GENERAL TREND WILL BE
DRYING OUT LATE SAT THROUGH MON. A BUBBLE SFC HIGH PRESSURE
CENTER IN NRN BC...MAYBE DUE IN PART TO COOLING TEMPS IN
CANADA...COULD BE STRONG ENOUGH FOR SOME EAST GAP WINDS ALONG
NORTHER OUTER COAST SUN TO MON. BY TUES ANOTHER DEEP SURFACE LOW
CENTER IS FCST TO SWING INTO THE SOUTHERN GULF AND UP THE OUTER
COAST WITH ANOTHER ROUND OF RAIN MID NEXT WEEK. MODELS SHOW THIS
AS A SLOW MOVER AND THE CENTER STAYS OFFSHORE. IF THAT IS HOW IT
ENDS UP THAN MORE WINDY CONDITIONS COULD DEVELOP IN DIXON ENTRANCE
AND SOUTHERN OUT COAST ABOUT TUES.

USED SREF MODEL TO BLEND INTO EXISTING FRI NIGHT THROUGH SAT NIGHT
FCST. AFTER THAT ADJUSTMENTS WERE MINOR AND INTERPOLATED TOWARD
NATIONAL CENTER GUIDANCE FOR AK. FORECAST CONFIDENCE OF OVERAL
TREND IS AT OR ABOVE AVERAGE. LOCALLY HIGHER WIND EFFECTS NEAR
TERRAIN IS WHAT BEARS WATCHING SAT THROUGH SUN PERIODS.

&&

.AJK WATCHES/WARNINGS/ADVISORIES...
PUBLIC...HIGH WIND WARNING FROM 1 AM TO 7 AM AKDT FRIDAY FOR AKZ023-026.
 	HIGH WIND WARNING FROM 10 PM THIS EVENING TO 7 AM AKDT FRIDAY
 	FOR AKZ027.
 	HIGH WIND WARNING FROM 1 AM TO 10 AM AKDT FRIDAY FOR AKZ028.
MARINE...STORM WARNING FOR PKZ033-035-036-041. GALE WARNING FOR
 	PKZ012-013-031-034-042. SMALL CRAFT ADVISORY FOR
	PKZ011-021-022-032-043-051-052.

&&

FRITSCH/TA

PRELIMINARY LOCAL STORM REPORT
NATIONAL WEATHER SERVICE JUNEAU AK
156 AM AKDT FRI SEP 23 2011

..TIME...   ...EVENT...      ...CITY LOCATION...     ...LAT.LON...
..DATE...   ....MAG....      ..COUNTY LOCATION..ST.. ...SOURCE....
            ..REMARKS..

0155 AM     NON-TSTM WND GST HYDABURG                55.21N 132.82W
09/23/2011  M64 MPH                             AK   ASOS

            64 MPH GUSTS AT 1256 AM AND 0116 AM. ALSO A 60 MPH JUST
            CAME IN AT 0136 AM.

&&

JBT

PRELIMINARY LOCAL STORM REPORT
NATIONAL WEATHER SERVICE JUNEAU AK
359 AM AKDT FRI SEP 23 2011

..TIME...   ...EVENT...      ...CITY LOCATION...     ...LAT.LON...
..DATE...   ....MAG....      ..COUNTY LOCATION..ST.. ...SOURCE....
            ..REMARKS..

0357 AM     NON-TSTM WND GST KETCHIKAN               55.34N 131.65W
09/23/2011  M64 MPH                             AK   ASOS

            GUST 64 MPH AT 3 AM. GUSTS 60 MPH AT 4 AM.

&&

JBT