Small Craft Advisory 555, NWS Juneau, AK

SOUTHEAST ALASKA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE JUNEAU AK
333 PM AKDT MON SEP 19 2011

.SHORT TERM... A STRONG LOW PRESSURE SYSTEM WILL MOVE INTO THE
WESTERN GULF TONIGHT. THIS SYSTEM IS ALREADY CAUSING GUSTS TO
STORM FORCE OVER THE NORTHERN GULF OUTSIDE WATERS AND ARE
EXPECTED TO INCREASE FOR THE REMAINING OUTSIDE WATERS THIS
EVENING AND INTO THE COASTAL LAND AREAS. FURTHER INLAND SITES
HAVE ALREADY BEEN GUSTING 25-30KT OUT OF THE SE. THESE WINDS WILL
CONTINUE TO INCREASE THROUGH THE EVENING WITH THE HIGHEST WINDS
EXPECTED AROUND MIDNIGHT AS THE FRONT ASSOC WITH THE LOW MOVES
INLAND. AREAS ALONG THE COAST SUCH AS SITKA AND CRAIG WILL SEE
WINDS REACHING 30-40MPH WITH HIGHER GUSTS. RAIN WILL ARRIVE WITH
THESE WINDS. LIGHT RAIN HAS ALREADY STARTED AT MOST SITES AND
WILL CONTINUE TO SPREAD INLAND...BECOMING HEAVY AT TIMES
OVERNIGHT. RAINFALL AMOUNTS OF UP TO 0.5-1IN IN 6HRS CAN BE
EXPECTED...WITH GREATEST RAINFALL AMOUNTS OVER AREAS WITH SW
FACING SLOPES AND ALONG THE COAST. THESE RAINFALL AMOUNTS
COMBINED WITH STRONG WINDS WILL LEAD TO THE RISK OF MUDSLIDES.
SMALL STREAMS WILL RISE IN AREAS WITH HEAVY RAINFALL BUT NOT
EXPECTED TO GO OUT OF THEIR BANKS. HOWEVER...LOCALIZED FLOODING
MAY BECOME AN ISSUE WITH LEAVES STARTING TO FALL OF TREES AND
PLUGGING DRAINS.

 OVERCAST SKIES AND RAIN WILL LIMIT THE DIURNAL TEMPERATURE
VARIATION TO JUST A FEW DEGREES...WITH LOWS RANGING IN THE UPPER
40S TO AROUND 50F AND HIGHS ON TUESDAY IN THE LOWER 50S.

 MODELS HAVE BEEN IN VERY GOOD AGREEMENT WITH THIS SYSTEM OVER
THE PAST SEVERAL DAYS KEEPING FORECASTER CONFIDENCE ABOVE
AVERAGE. UPDATED THE THE FORECAST WITH THE LATEST NAM12 AND GFS
AS THEY INITIALIZED THE BEST.

&&

.LONG TERM...REMNANTS OF 973 MB LOW OVER KODIAK AT THE START OF
THE LONG TERM ON TUE NIGHT WITH A SECOND GALE FORCE LOW DEVELOPING
IN THE NORTH PACIFIC AND TRACKING INTO THE AK GULF BY WED. THIS
LOW WILL DEEPEN TO AROUND 966 MB WITH GALE FORCE WINDS DEVELOPING
FROM SOUTH TO NORTH. IN ADDITION TO THE STRONG WINDS LONG FETCH OF
MOISTURE CONNECTED TO THE LOW WILL BRING HEAVY RAINS TO THE REGION
AGAIN. MODELS WERE IN GOOD AGREEMENT WITH RESPECT TO THE TIMING OF
THE LOW BUT GFS STILL A BIT FASTER COMPARED TO THE EC/NAM. AS THIS
LOW WEAKEN TO AN OPEN WAVE TROUGH AS IT MOVE NEAR PRINCE WILLIAM
SOUND A WEAK HIGH PRESSURE RIDGE WILL BUILD OVER THE PANHANDLE.
ANOTHER STRONGER LOW PRESSURE SYSTEM WILL AGAIN TRACK INTO THE
SOUTHEAST GULF FROM THE NORTH PACIFIC THURSDAY EVENING. MODELS
HAVE THE LOW CENTER DEEPENING TO AROUND 960 MB BUT TIMING
DIFFERENCES EXITS WITH THE GFS AROUND 18 HOURS FASTER THAN THE EC.
AS WITH THE PREVIOUS WEEKS LOWS WILL SEE STRONG WINDS AND HEAVY
RAIN FOR FRIDAY. HIGH PRESSURE BUILDING OVER THE PANHANDLE OVER
THE WEEKEND, DID INCREASE POPS FOR SAT BUT AT THIS TIME SUN
LOOKING A BIT DRIER.

DUE TO GOOD MODEL AGREEMENT AT THE START OF THE LONG TERM USED A
BLEND OF GFS AND NAM WITH INHERITED GRIDS. KEPT WITH GFS FOR THE
WED LOW PRESSURE SYSTEM AS IT KEEP WITH THE MORE PROGRESSIVE TRACK
IN THE PREVIOUS FORECAST. SWITCHED BACK TO ECMWF THEN TO HPC,
WHICH USED EC ENSEMBLES, SHOWING THE SLOWER TIMING WITH THE
FRIDAY LOW PRESSURE SYSTEM. DID SEE AN INCREASE IN WINDS ON
WEDNESDAY AND FRIDAY, HOWEVER TONED THEM DOWN SLIGHTLY FOR A
SMOOTHER TRANSITION.

HYDROLOGICAL. THE SERIES OF LOW PRESSURE SYSTEMS ENTERING THE GULF
WILL EACH BRING HIGH WINDS AND AMPLE PRECIPITATION WITH QPF RATES
OF UP TO 2 INCHES IN 12 HOURS. THE CONTINUED RAIN WILL STATURE THE
GROUND AND RAISE RIVER LEVELS...HOWEVER RIVERS WILL STILL BE BELOW
ACTION STAGE AS FREEZING LEVELS ARE LOWERING KEEPING PRECIP AT
HIGH ELEVATIONS FROZEN RESULTING IN LESS RUN OFF. MUDSLIDES WILL
BE A POSSIBILITY DUE THE CONTINUED PRECIP AND HIGH WINDS HELPING
TO LOOSEN SOIL. BLOCKED DRAINS FROM THE HEAVY RAIN AND FALLING
LEAVES ARE ALSO POSSIBLE.

.AJK WATCHES/WARNINGS/ADVISORIES...
PUBLIC...NONE.
MARINE...STORM WARNING FOR PKZ036-041>043-051-052.
         GALE WARNING FOR PKZ021-022-032>035-053.
         SMALL CRAFT ADVISORY FOR PKZ011>013-031.

&&

HANNON/PRB