Small Craft Advisory 662, NWS Anchorage, AK

AREA FORECAST DISCUSSION
SOUTHCENTRAL AND SOUTHWEST ALASKA
500 AM AKDT SUN AUG 23 2009

.ANALYSIS AND UPPER LEVELS...
THE UPPER RIDGE OVER THE GULF HAS BEEN ALMOST ENTIRELY ERODED BY A
STRONG TROUGH OVER THE EASTERN BERING THAT IS SLIDING EASTWARD. AN
ASSOCIATED BAND OF RAIN SHOWERS OVER SOUTHWEST ALASKA IS CROSSING
OVER THE ALASKA AND ALEUTIAN RANGES AND MOVING INTO SOUTHCENTRAL THIS
MORNING. SEVERAL VERY WEAK LOWS ALONG THE NORTH GULF COAST AND
PRODUCING SCATTERED SHOWERS. A DEVELOPING LOW IN THE BASE OF THE
EASTERN BERING SEA TROUGH IS THE FIRST IN A SERIES OF LOWS THAT WILL
MOVE SOUTHEAST AND DIG OUT A DEEP LONGWAVE TROUGH IN THE GULF. HIGH
PRESSURE OVER THE BERING SEA IS ALSO WEAKENING AND GIVING WAY TO
GENERALLY ZONAL FLOW.

.MODEL DISCUSSION...
THE MAJOR MODELS ALL AGREE ON THE BASIC MOVEMENT OF WEATHER SYSTEMS
THROUGH THE END OF THE WEEK ACROSS THE ENTIRE AREA. SOME TIMING
DIFFERENCES EXIST...ESPECIALLY IN REGARDS TO THE REMNANTS OF TYPHOON
VAMCO THAT TRAVERSE THE ALEUTIAN ISLANDS MIDWEEK. FOR THIS
FEATURE...THE GFS AND ECMWF HAVE COME INTO BETTER AGREEMENT...WITH
THE NAM NOW THE EXCEPTION WITH ITS SLOWER SPEED. THUS WILL USE THE
GFS/ECMWF SOLUTION FOR THE MORNING FORECAST BEGINNING MIDWEEK AND
TRANSITION TO THE ECMWF IN THE EXTENDED.

.SHORT TERM FORECAST...
.EAST OF THE ALASKA RANGE...
AS THE FRONT OVER WESTERN ALASKA MOVES INTO THE AREA THIS MORNING
SHOWERS ARE EXPECTED TO SPREAD EAST THROUGHOUT THE DAY FROM THE KENAI
PENINSULA TO THE SUSITNA VALLEY. SHOWERS ALREADY IMPACTING THE COAST
AND PRINCE WILLIAM SOUND WILL INTENSIFY THROUGHOUT THE DAY. BY THIS
EVENING MOST LOCATIONS SHOULD BE SEEING PERIODS OF LIGHT RAIN. A
DECENT POOL OF COLD AIR BEHIND THE FRONT WILL ALLOW STRONG NORTHWEST
WINDS TO DEVELOP...ESPECIALLY THROUGH THE USUAL GAPS IN THE ALEUTIAN
RANGE...PRIMARILY IMPACTING INTERESTS AROUND KODIAK ISLAND AND THE
BARREN ISLANDS THROUGH MONDAY AFTERNOON.

.WEST OF THE ALASKA RANGE...
RAIN LINGERING ALONG THE ALASKA AND ALEUTIAN RANGES THIS MORNING WILL
SLOWLY DIMINISH THROUGH THE AFTERNOON HOURS. A WEAK SECONDARY FRONT
IS MOVING THROUGH THE KUSKOKWIM DELTA AND WILL KEEP SCATTERED SHOWERS
ACROSS MUCH OF SOUTHWEST ALASKA TODAY. MODERATE WESTERLY ONSHORE
WINDS WILL KEEP CONDITIONS CLOUDY AND COOL TODAY. SKIES SHOULD BEGIN
TO CLEAR AS HIGH PRESSURE IN THE CENTRAL BERING MOVES INTO THE AREA
TONIGHT.

.BERING SEA/ALEUTIANS...
TRANQUIL WEATHER IS COMING TO AN END AS A LOW APPROACHING THE WESTERN
BERING MOVES INTO THE AREA BRINGING RAIN AND GALE FORCE WINDS TO THE
WESTERN ALEUTIANS TODAY AND SPREADING TO THE CENTRAL AND EASTERN
ALEUTIANS TONIGHT AND MONDAY. AFTER A SHORT BREAK TUESDAY...STRONG
WINDS RETURN TO THE AREA WEDNESDAY AS THE LEFTOVERS OF TYPHOON VAMCO
QUICKLY MOVE IN WEDNESDAY.

.LONG TERM FORECAST...A LONGWAVE TROUGH IN THE GULF WILL KEEP VERY
UNSETTLED WEATHER LARGELY SOUTH OF MAINLAND ALASKA FOR MUCH OF THE
WEEK. HOWEVER...DEPENDING ON THE EXACT POSITION OF THE LOW IN THE
GULF...PARTS OF SOUTHCENTRAL MAY SEE PERIODS OF RAIN MOVE IN FROM THE
EAST TOWARDS THE END OF THE WEEK. BY NEXT WEEKEND...THERE ARE SOME
INDICATIONS THE LONGWAVE TROUGH MAY START TO SHIFT BACK TO THE BERING
SEA...BUT THIS IS STILL FAR FROM CERTAIN. IN LIGHT OF THE FACT THAT
MODELS HISTORICALLY STRUGGLE DURING THE SPRING AND FALL TRANSITION
SEASONS...WILL REMAIN RETICENT TO PUTTING TOO MUCH FAITH IN ANY
PARTICULAR MODEL AT THIS POINT.

.AER/ALU...WATCH/WARNING SUMMARY
PUBLIC...NONE.
MARINE...NONE.
FIRE WEATHER...NONE.

AMD AUG 09