221
FXUS02 KWBC 261819
PMDEPD
EXTENDED FORECAST DISCUSSION
NWS HYDROMETEOROLOGICAL PREDICTION CENTER CAMP SPRINGS MD
218 PM EDT TUE AUG 26 2008
VALID 12Z FRI AUG 29 2008 - 12Z TUE SEP 02 2008
A PORTION THE POLAR VORTEX OVER NORTHWEST CANADA APPEARS TO BE THE
DOMINANT FEATURE TODAY...ALLOWING FOR THE FORMATION OF A WEST
COAST TROUGH. OUT EAST...THE SITUATION IS MUCH MORE TRICKY DUE TO
DAY-TO-DAY AND RUN-TO-RUN VARIATIONS OF ENERGY MOVING THROUGH NEW
ENGLAND...AND ENERGY MOVING DOWN THE BREAK IN THE SUBTROPICAL
RIDGE TOWARDS THE GULF COAST. OVERALL...CONFIDENCE IN TODAYS
PREFERRED SOLUTION /00Z NCEP ENSEMBLE MEAN AND 00Z GFS/ IS LOW DUE
THE AFOREMENTIONED CHANGES IN THE GUIDANCE. OUT WEST...A LOOK AT
THE 12Z GUIDANCE AND COORDINATION WITH THE ALASKA MEDIUM RANGE
DESK LED TO SOME ACCELERATION TO THE COLD FRONT...NOW MOVING INTO
WASHINGTON AT THE END OF THE PERIOD. THIS...ALONG WITH GUSTAVS
TRACK...WERE THE ONLY CHANGES MADE TO THE MORNING SET OF
PRESSURES.
WEST...
WHILE THE MODELS AGREE ON TROUGHING...THEY DISAGREE AS TO HOW
AMPLIFIED THE SYSTEM WILL BE. THE 00Z ECMWF IS THE MOST
AMPLIFIED...WITH THE 00Z UKMET/00Z ECMWF ENSEMBLE MEAN SHOW AN
INTERMEDIATE SOLUTION...WHILE THE 00Z GFS/00Z NCEP ENSEMBLE MEAN
ARE THE WEAKEST BECAUSE OF THEIR STRONGER SYSTEM IN THE NORTHEAST
PACIFIC. FOR NOW...FAVOR A BLEND OF THE 00Z GFS/NCEP ENSEMBLE
MEAN...BUT THIS CHOICE IS ONE OF LOW CONFIDENCE AND WILL BE
COORDINATED WITH THE ALASKA MEDIUM RANGE DESK LATER THIS MORNING.
SOUTHEAST...
GUSTAVS TRACK IS ONE BIG QUESTION MARK...WHICH IS IMPLIED BY
CURRENT OPERATIONAL GUIDANCE AND THEIR LACK OF CONTINUITY
/PARTICULARLY IN THE ECMWF/ SINCE YESTERDAY. THE ECMWF AND
CANADIAN ENSEMBLE MEMBERS SHOW TREMENDOUS SPREAD...RANGING IN
SOLUTIONS FROM RECURVATURE OFF THE EAST COAST OF FLORIDA AND THE
CAROLINAS TO A WESTWARD TRACK THROUGH THE BAY OF CAMPECHE. THE
MEAN FLOW PATTERN NEAR THE GULF COAST/SOUTHEAST CONTINUES TO
INDICATE A BREAK IN THE SUBTROPICAL RIDGE EARLY IN THE
PERIOD...WITH A COUPLE PIECES OF GUIDANCE SHOWING AN UPPER LOW
NEAR THE CENTRAL GULF COAST LATER ON /SEEN ON ALL THE GUIDANCE
THIS TIME YESTERDAY/ WHICH IS A COMMON SUMMERTIME DEVELOPMENT.
EVEN MODELS THAT SHIFTED A BIT TO THE WEST /THE CANADIAN/ SHOW
THIS FEATURE AND COLLAPSE THE STEERING PATTERN OVER THE CENTRAL
GULF OF MEXICO BOTH AT THE SURFACE AND MID LEVELS OF THE
TROPOSPHERE. WITH THE AMPLIFICATION EXPECTED IN THE RIDGE ACROSS
THE EAST...THERE IS ROOM FOR GUSTAV TO GAIN LATITUDE IF IT REMAINS
A DEEP CYCLONE...WHICH IS ONLY AN IF WHEN CONSIDERING THE GFS
SOLUTION. THE 16Z CALL WITH NHC SHIFTED THE TRACK SOMEWHAT WEST
OF THE MORNING PRELIMS...IMPLYING A CYCLONE MOVING TOWARDS THE
CENTRAL GULF COAST BEYOND THE MEDIUM RANGE PERIOD.
NORTHEAST/EASTERN CANADA...
ONLY THE GFS AND CANADIAN CLOSE OFF ENERGY NEAR NEW
ENGLAND/ATLANTIC CANADA EARLY NEXT WEEK...AS THE ECMWF
SIGNIFICANTLY BACKED OFF ON ITS 00Z RUN. THE TREND IN BOTH THE
GFS AND ECMWF FROM THIS TIME YESTERDAY IS TOWARDS A WEAKER AND
MORE PROGRESSIVE SYSTEM. HOWEVER...THE 00Z NCEP ENSEMBLE MEAN WAS
DEEPER THAN MUCH OF THE GUIDANCE WITH THIS FEATURE...THOUGH
WAVELENGTH SEPARATION BETWEEN THE WEST COAST TROUGH AND THIS
SYSTEM AS WELL AS REMNANT RIDGING OVER THE DAVIS STRAIT/SOUTHERN
GREENLAND HINT THAT A CLOSED CYCLONE IS POSSIBLE ACROSS NEW
ENGLAND. THE LESS SAID ABOUT THE 00Z CANADIAN MODELS HURRICANE
MOVING INTO NEW ENGLAND...THE BETTER. THINK A 00Z GFS/NCEP
ENSEMBLE MEAN IS THE BEST WAY TO GO AT THE CURRENT TIME...BUT
CONFIDENCE IS LOW IN ANY INDIVIDUAL PIECE OF GUIDANCE IN THIS
REGION.
ROTH
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