Small Craft Advisory 577, NWS Juneau, AK

SOUTHEAST ALASKA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE JUNEAU AK
207 PM AKDT WED SEP 18 2013

.SHORT TERM...CONDITIONS PROGRESSING AS FORECAST WITH REGARD TO
AN APPROACHING STORM FORCE LOW THAT WILL GENERATE HIGH WINDS OVER
THE SOUTHERN PANHANDLE AND PRODUCE HEAVY RAIN OVER MOST OF
SOUTHEAST ALASKA DURING THIS SHORT TERM FORECAST PERIOD. THESE
CONDITIONS WILL EXTEND INTO THE LONG RANGE FORECAST PERIODS
BEGINNING THURSDAY NIGHT.

 SATELLITE IMAGERY TODAY HAS BEEN SHOWING AN UPPER LEVEL
LOW/TROUGH DIGGING SOUTH FROM THE WESTERN GULF INTO THE NORTH
PACIFIC AND PRESSING UP AGAINST THE EXISTING FRONTAL BOUNDARY.
OVERALL AGREEMENT AMONGST THE MODELS IS VERY GOOD, WITH BOTH GEM
AND ECMWF DEVELOPING A SECONDARY LOW OUT OF THIS TROUGH WEST OF
THE PRIMARY LOW. WHETHER OR NOT THIS LOW FORMS, THE COLD UPPER
LEVEL AIR ASSOCIATED WITH THE TROUGH AND A DIGGING DRY SLOT IN
WATER VAPOR IMAGERY WILL TEND TO STRENGTHEN THE SYSTEM
SIGNIFICANTLY OVER THE NEXT 24 HOURS. FORECAST CENTRAL PRESSURE
BY THURSDAY AFTERNOON RANGING FROM 971 TO 977 MB APPROX. 300 NM
SOUTHWEST OF THE DIXON ENTRANCE WITH STORM FORCE WINDS OVER THE
EXTREME SOUTHEASTERN GULF.

 HIGH WIND WATCH HAS BEEN REPLACED BY A HIGH WIND WARNING FOR THE
SOUTHERN PANHANDLE, PUBLIC ZONES 27 AND 28, BEGINNING THURSDAY
MORNING. ALSO INCLUDED STRONG WIND HEADLINES FOR ZONES 23 AND 26.
THINK THE HIGHER GUSTS WILL BE SEEN PRIMARILY ALONG THE EASTERN
SHORE OF BARANOF ISLAND FOR ZONE 23. FOR ZONE 26, THINK THE
STRONGEST WINDS AND GUSTS TO BE SEEN OVER KI ISLAND AND
ELSEWHERE SOUTH OF SUMNER STRAIT. HAVE ALSO INCLUDED A STORM
WARNING FOR CLARENCE STRAIT, WHERE WINDS OFTEN TURN OUT TO BE
STRONGER THAN ORIGINALLY ANTICIPATED IN SUCH SITUATIONS AS THIS.

 WATER VAPOR IMAGERY IS ALSO REVEALING VERY HIGH PRECIPITABLE
WATER VALUES AND MODELS ARE ALL IN AGREEMENT ON A VERY LARGE AREA
OF HEAVY RAIN ASSOCIATED WITH THE OCCLUDED FRONT THAT WILL MOVE
NORTH OVER THE PANHANDLE BEGINNING LATE TONIGHT. NO HYDROLOGICAL
PRODUCTS ISSUED WITH THE AFTERNOON FORECAST, BUT THE SITUATION
WILL BE MONITORED CLOSELY.

 USED A BLEND OF ECMWF AND GEM TO CAPTURE THE LOW DEVELOPING
ALONG THE FRONTAL BOUNDARY. RESULTANT WIND DIRECTIONS OVER THE
GULF CHANGED SLIGHTLY, BUT USED WIND SPEEDS AS ISSUED BY PREVIOUS
SHIFT. INCREASED WINDS TO STORM FORCE OVER CLARENCE STRAIT AND TO
MEET HIGH WIND WARNING CRITERIA OVER PUBLIC ZONES IN RESPONSE TO
80 KT LOW LEVEL JET CORE OVER SOUTHERN PANHANDLE IN BOTH ECMWF
AND GFS. FORECAST CONFIDENCE IS ABOVE AVERAGE.

.LONG TERM...MOST ADJUSTMENTS TO THE FORECAST WERE FOR THU NIGHT
INTO FRI. GENERALLY KEPT PREVIOUS FORECAST OF LOW TRACK ACROSS
THE ERN GULF THU NIGHT INTO FRI. MODELS WERE STILL HAVING SOME
ISSUES ON EXACTLY HOW THE LOW WILL EVOLVE WITH SOME SHOWING
MULTIPLE LOW CENTERS WHILE OTHERS SHOWED ONE MAIN CENTER. STUCK
WITH THE ONE CENTER IDEA AT THIS POINT. DID MAKE SOME UPWARD
ADJUSTMENTS TO THE WINDS OVER THE SRN AREAS...AND ENDED UP
CONTINUING THE HIGH WIND WARNING TO ABOUT MIDDAY FRI FOR ZONES 27
AND 28. 925 MB WINDS ON THE GFS WERE IN THE 60-75 KT RANGE DURING
THIS TIME. EXTENDED THE TIME FRAME OF STORM FORCE WINDS FOR
CLARENCE STRAIT TO COVER THU NIGHT AS WELL. CONTINUED THE STRONG
WIND HEADLINES FOR ZONES 23 AND 26 THRU FRI EVENING. DEPENDING ON
HOW FAST THE LOW WEAKENS AS IT GETS INTO THE NE GULF...MAY NEED
STRONG WIND HEADLINES FOR THE N-CENTRAL AREA FOR LATER FRI INTO
FRI EVENING.

FOR THE WEEKEND AND BEYOND...STAYED THE COURSE FOR NOW. MODELS
STILL JUMPING AROUND ON TRACK OF WEEKEND LOW MOVING ACROSS THE
GULF...BUT SEEM TO BE SLOWLY CONVERGING ON A MORE SLY TRACK. THEY
ALSO HINT AT ANOTHER SYSTEM MOVING INTO THE AREA AROUND THE TUE-WED
PERIOD. OVERALL...PATTERN LOOKS TO REMAIN ACTIVE OVER THE NEXT
WEEK.

.AJK WATCHES/WARNINGS/ADVISORIES...
PUBLIC...STRONG WIND FROM THURSDAY MORNING THROUGH FRIDAY EVENING FOR
     AKZ023-026.
         HIGH WIND WARNING FROM 7 AM THURSDAY TO 1 PM AKDT FRIDAY FOR
     AKZ027-028.
MARINE...STORM WARNING FOR PKZ036-041.
         GALE WARNING FOR PKZ033-035-042-043.
         SMALL CRAFT ADVISORY FOR PKZ021-022-031-032-034-051-052.

&&

FRITSCH/RWT