Small Craft Advisory 556, NWS Juneau, AK

SOUTHEAST ALASKA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE JUNEAU AK
515 AM AKDT TUE SEP 20 2011

.SHORT TERM...MATURE VERTICALLY STACKED LOW SE OF KODIAK 967 MB
AT 12Z TODAY HAS STARTED TO FILL. THIS SYSTEM HAS CAPTURED
SIGNIFICANT TROPICAL MOISTURE AND THE COLD AIR SUPPORT IS NOT VERY
STRONG...-26C AT 500 HPA AS PER 12Z KODIAK RAOB. SYSTEM STILL IS
IN UPPER LEFT QUAD OF A TRANSPACIFIC JET FROM THE HIMALAYAS AND
HAS DEVELOPED ITS OWN SOUTHERLY BRANCH ALONG 140W OR SO. THE
ASSOCIATED FRONT NOW MOVING ONTO THE SE AK COAST AS OF 12Z WAS
STRONG AND HAD DRIVEN STORM FORCE WINDS PLUS HUGE SEAS. BOTH RADAR
AND SATELLITE IMAGERY SHOW A BACK EDGE TO THIS FRONT BUT WITH SO
MUCH MOISTURE BEHIND THE FRONT EXPECTING LITTLE OR NO RESPITE FROM
RAIN IN THE NEXT 24 HOURS.

 MOST INTERESTING IS A RAPID DEVELOPMENT ON THE S SIDE OF THIS
MONSTER-SIZED SYSTEM. A CLOSED CENTER HAS FORMED NEAR 45N 152W OR
SO AS PER SATELLITE IMAGERY AT 13Z. AGAIN THE JET IS IN GOOD
SUPPORT AND ALL 20/00Z MODELS AGREE THAT THIS SYSTEM WILL BOMB
BUT BY HOW MUCH? INDICATED GALES TO HIT SOUTHERN OUTSIDE WATERS
WED NIGHT AS PER LOCAL WRF MODEL AND 20/12Z AK-GFS-40 MODEL SFC
WIND. CONCERNED THAT STORMS ARE IN ORDER IF BOUNDARY LAYER WINDS
USED AS PER MODELS NOW ARRIVING. WILL NEED SOME WIND HEADLINES
FOR SOUTHERN AND COASTAL ZONES. CONFIDENCE MODERATE. MAYBE MORE
WIND NEEDED.

&&

.LONG TERM...MODELS ARE IN FAIR AGREEMENT THROUGH THURSDAY NIGHT
WITH THE STORM FORCE LOW IN THE EASTERN GULF WEDNESDAY MORNING
WEAKENS AND TRACKS NORTH TO NEAR YAKUTAT BAY BY WEDNESDAY
EVENING...THEN FARTHER NORTH TO ALASKA INTERIOR AS AN OPEN WAVE. A
WEAK RIDGE OF HIGH PRESSURE BUILDS ACROSS THE FORECAST DOMAIN ON
THURSDAY WITH ANOTHER DEVELOPING STORM FORCE LOW ENTERING THE
EASTERN GULF BY THURSDAY NIGHT. THE GFS SHOWS A BETTER CONSISTENCY
THAN OTHER MODELS AND WAS USED TO REFRESH THE INHERITED GRIDS
THROUGH THURSDAY NIGHT.

 STORM FORCE WINDS WILL EXPAND FROM SOUTH TO NORTH ACROSS THE
OUTER COASTAL WATERS WEDNESDAY...EASE TO GALE LATE WEDNESDAY THEN
BACK TO STORM FORCE WITH THE NEXT SYSTEM THURSDAY AND FRIDAY.
MODERATE TO HEAVY RAINFALL WILL ACCOMPANY THE STRONG GUSTY WINDS.
KEPT THE STRONG WINDS HEADLINE FOR PANHANDLE COASTAL SECTIONS FROM
ELFIN COVE SOUTH TO THE SOUTHERN AREAS THROUGH LATE WEDNESDAY. THE
SECOND STORM FORCE LOW WILL ONCE AGAIN BRING THE STRONG GUSTY
WINDS AND MODERATE TO HEAVY RAINFALL TO THE PANHANDLE COAST ON
THURSDAY AND THURSDAY NIGHT. IN RESPONSE TO THE CONTINUED ABOVE
NORMAL RAINFALL...LOCAL STREAMS AND RIVERS WILL STEADILY RISE
THROUGH LATE THURSDAY THEN THE WATER LEVELS WILL RETURN TO AVERAGE
NORMAL FLOW TOWARDS THE WEEKEND.

 FROM FRIDAY ONWARD...MODELS REMAIN IN GENERAL AGREEMENT WITH
HIGH PRESSURE BUILDING OVER BRITISH COLUMBIA WITH RELATIVELY DRY
WEATHER OVER THE WEEKEND. WITH GROWING UNCERTAINTY FOR A
DEVELOPING STORM IN THE NORTH PACIFIC IMPOSING ITS TRACK TO FAR
SOUTHERN GULF THROUGH EARLY NEXT WEEK...USED THE HPC GUIDANCE FOR
THE PRESSURE FIELD FROM FRIDAY THROUGH THE END. THE POP FIELD WERE
BLENDED WITH THE GFS AND ECMWF.

&&

.AJK WATCHES/WARNINGS/ADVISORIES...
PUBLIC...NONE.
MARINE...GALE WARNING FOR PKZ033-035-036-041>043-051-052.
         SMALL CRAFT ADVISORY FOR PKZ011>013-021-022-031-032-034-053.

&&

JC/AHN