Small Craft Advisory 558, NWS Juneau, AK

SOUTHEAST ALASKA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE JUNEAU AK
358 PM AKDT MON AUG 17 2015

.SHORT TERM...STRONG WINDS AND HEAVY RAIN FOR THE NORTHERN HALF OF
THE PANHANDLE THROUGH TUESDAY DAYTIME.

 THE SHORT TERM FORECAST PERIOD IS VERY ACTIVE FOR SOUTHEAST
ALASKA. AN INTENSIFYING LOW NEAR KODIAK ISLAND IS TRACKING
NORTHEASTWARD INTO PRINCE WILLIAM SOUND OVERNIGHT, THEN JUMPING
INLAND INTO SOUTHEAST MAINLAND ALASKA AND THEN INTO SOUTHERN
YUKON. MEANWHILE, A STRONG RIDGE OF HIGH PRESSURE IS MAINTAINING
ITS CONTROL OVER THE NORTH PACIFIC OCEAN. THE LOW IS EXPECTED TO
DROP DOWN TO 993 MB OVER YUKON, WHILE PRESSURE WILL BE AROUND
1020 MB OVER THE SOUTHERN END OF THE PANHANDLE. THE COMBINED
SYSTEM IS CREATING AN ANOMALOUSLY STRONG SOUTHERLY PRESSURE
GRADIENT OVER SOUTHEAST ALASKA. THIS WILL GENERATE SIGNIFICANT
WINDS ACROSS THE NORTHERN HALF OF THE PANHANDLE.

 STRONG WIND GUSTS EXCEEDING 40 MPH ARE EXPECTED IN AREAS
INCLUDING YAKUTAT, ELFIN COVE, GUSTAVUS, HOONAH, HAINES, SKAGWAY,
JUNEAU, AND SITKA OVERNIGHT TONIGHT INTO TUESDAY MORNING. FOR
SKAGWAY, DO EXPECT WIND GUSTS UP TO 65 MPH AND THUS CONTINUE TO
HAVE THE HIGH WIND WARNING FOR THEM. ALSO INTRODUCE 50 KT
SUSTAINED WINDS WITH 10 FEET WAVE HEIGHT FOR NORTHERN LYNN CANAL.
GALE FORCE WINDS WILL BE FOUND IN LYNN CANAL, CROSS SOUND, ICY
STRAIT, GLACIER BAY, STEPHENS PASSAGE, AND CHATHAM STRAIT TONIGHT
INTO TUESDAY. WINDS WILL START TO DIMINISH AT THE END OF THE SHORT
TERM FORECAST PERIOD TUESDAY AFTERNOON.

 HEAVY RAIN IS ANOTHER BIG STORY MAKER FOR THE SHORT TERM FORECAST
PERIOD. 2 TO 4 INCHES OF RAIN EXPECTED IN PARTS OF NORTHERN
PANHANDLE. 4 TO 6 INCHES ALONG THE COAST FROM NORTH OF SITKA TO
YAKUTAT...HIGHEST RAINFALL AMOUNTS OVER THE UPSLOPE AREA OF
MOUNTAINS. RAINFALL RATE AS HIGH AS 1 INCH PER HOUR WILL TAKE
PLACE OVERNIGHT TONIGHT. FOR AREAS SUCH AS YAKUTAT, THIS WILL BE A
2 TO 5 YEAR RAIN EVENT. KEEP THE FLOOD WATCH FROM YAKUTAT TO AREAS
AS FAR SOUTH AS SITKA AND ANGOON. THE FLOOD WATCH FOR CENTRAL
PANHANDLE (PETERSBURG, WRANGELL, AND KAKE) WAS CANCELLED AS QPF
AMOUNTS ARE NOT AS HIGH AS ANTICIPATED. PLEASE REFER TO FLOOD
WATCH STATEMENT FOR MORE INFORMATION. THE SITUATION ON HEAVY RAIN
WILL BE MONITORED CLOSELY AND THE STATEMENT WILL BE UPDATED THIS
EVENING.

CHANGES ARE MINOR TODAY. REFRESH THE INHERITED GRIDS WITH NAM
MODEL AS IT IS THE MOST SKILLFUL IN PREDICTING THE PRESSURE
GRADIENT OVER SOUTHEAST ALASKA. FOR RAINFALL AMOUNTS, UTILIZE
GUIDANCE FROM RIVER FORECAST CENTER. FORECAST CONFIDENCE ON THE
HEAVY RAIN AND STRONG WIND IS ABOVE AVERAGE.

.LONG TERM...THE RAIN EVENT FROM SHORT TERM WILL JUST BE STARTING
TO SETTLE DOWN AS WE GET INTO TUE NIGHT AND WED. THE ATMOSPHERIC
RIVER WILL HAVE WEAKENED NOTICEABLE BY TUE EVENING AND WILL BE
MOVING TO THE SE OUT OF THE PANHANDLE AND INTO COASTAL BRITISH
COLUMBIA. RAIN/SHOWERS WILL STILL BE PRESENT IN THE CONTINUED
WESTERLY FLOW BUT WITH THE MAIN MOISTURE PLUME MOVING OUT OF THE
AREA AMOUNTS WILL NOT BE AS GREAT. WINDS LIKEWISE WILL BE ON THE
DOWNWARD TREND AS PRESSURE GRADIENTS ACROSS THE GULF CONTINUE TO
WEAKEN IN THE WAKE OF THE MAIN PARENT LOW MOVING NE INTO CANADA.
20 TO 30 KT WINDS ACROSS THE GULF WILL BE THE RULE OF TUE EVENING
BUT WILL GRADUALLY DIMINISH TO 20 KT BY WED EVENING.

FOR THE REST OF THE LONG RANGE, UPPER LEVEL PATTERN REMAINS
RATHER PROGRESSIVE WITH A RATHER FLAT RIDGE OVER THE WESTERN GULF
THROUGH LATE WEEK. THIS RIDGE WILL HAVE ONE WEAK SHORT WAVE TROUGH
MOVE THROUGH IT ON THU BEFORE IT IS SHOVED OUT OF THE WAY BY A
STRONGER SHORT WAVE TROUGH FOR NEXT WEEKEND. FROM HERE THE PATTERN
TRENDS TOWARD A HIGHER AMPLITUDE PATTERN AS THE TROUGH SLOWS DOWN
OVER THE GULF WHILE A RIDGE BUILDS OVER THE EASTERN ALEUTIANS AND
ALASKA PENINSULA.

AT THE SURFACE THE TREND IS FOR CONTINUED WET WEATHER FOR MOST OF
THE LONG RANGE PERIOD. TUE NIGHT INTO WED FEATURES CONTINUED
ONSHORE FLOW WITH A WEAK UPPER TROUGH MOVING THROUGH THU BUT NO
ATMOSPHERIC RIVER SO RAIN WILL CONTINUE THROUGH AT LEAST THU BUT
ANY HEAVY RAINFALL IS NOT EXPECTED. THU NIGHT INTO FRI MIGHT BE
THE ONLY DRY PERIOD OUT OF THE WEEK AS THE WEAK RIDGE OVER THE
GULF BUILDS UP ENOUGH TO TURN FLOW MORE NW AND N. IT MIGHT BE
ENOUGH FOR SOME SUN TO PEAK THROUGH THE CLOUDS. AS SUCH HAVE PUT
SOME MOSTLY CLOUDY SKIES WITH SOME AREAS OF PARTLY CLOUDY HERE AND
THERE FOR THU NIGHT INTO FRI.

INTO THE WEEKEND, THE NEXT STRONGER TROUGH WILL BE ENTERING THE
GULF. MODELS ARE HAVING SOME DIFFICULTIES AS TO THE STRENGTH OF
THE SURFACE FEATURE AS WELL AS TIMING. THE GFS IS THE ON THE
WEAKER SIDE WITH A 1004 MB LOW IN THE CENTRAL GULF FRI NIGHT. THE
ECMWF AND CANADIAN MEANWHILE ARE SUGGESTING AROUND 991 MB AND 994
MB RESPECTIVELY WITH SMALL CRAFT WINDS ACROSS MOST OF THE SOUTHERN
HALF OF THE GULF. OF THE THREE THE ECMWF HAS SO FAR SEEN THE BEST
CONSISTENCY BETWEEN INDIVIDUAL RUNS SO DECIDED TO LEAN IN THAT
DIRECTION AS WELL AS THE WPC (FAVORED THE ECMWF WITH SOME EMPHASIS
ON ITS ENSEMBLE MEANS) FOR THE WEEKEND. IN ANY CASE, THE WEEKEND
IS LOOKING WET FOR A GOOD PORTION OF THE PANHANDLE WITH POSSIBLY
SOME GUSTY WINDS ALONG SOME OF THE INNER CHANNELS AND OUTER COAST.

&&

.AJK WATCHES/WARNINGS/ADVISORIES...
PUBLIC...FLOOD WATCH FROM 7 PM AKDT THIS EVENING THROUGH TUESDAY EVENING
     FOR AKZ017>025.
         STRONG WIND FROM 10 PM AKDT THIS EVENING THROUGH TUESDAY
     AFTERNOON FOR AKZ022-025.
         STRONG WIND FROM 1 AM AKDT TUESDAY THROUGH TUESDAY MORNING FOR
     AKZ020-021-023.
         STRONG WIND FROM 1 AM AKDT TUESDAY THROUGH TUESDAY EVENING FOR
     AKZ019.
         HIGH WIND WARNING FROM 4 AM TO 7 PM AKDT TUESDAY FOR AKZ018.
         STRONG WIND FROM 10 PM AKDT THIS EVENING THROUGH LATE TONIGHT
     FOR AKZ018.
MARINE...STORM WARNING FOR PKZ012.
         GALE WARNING FOR PKZ011-013-021-022-031-032-043-051.
         SMALL CRAFT ADVISORY FOR PKZ033>036-041-042-052-053.

&&

RCL/EAL

VISIT US AT HTTP://WWW.WEATHER.GOV/JUNEAU