111
FXUS02 KWBC 251837
PMDEPD
EXTENDED FORECAST DISCUSSION
NWS HYDROMETEOROLOGICAL PREDICTION CENTER CAMP SPRINGS MD
236 PM EDT TUE AUG 25 2009
VALID 12Z FRI AUG 28 2009 - 12Z TUE SEP 01 2009
TELECONNECTIONS FOR A NEGATIVELY ANOMALY IN THE NORTHEAST PACIFIC
WHICH FADES LATE IN THE PERIOD FAVORS RIDGING IN WESTERN NORTH
AMERICA AND DOWNSTREAM TROUGHING ACROSS EASTERN CANADA/THE
NORTHEAST/GREAT LAKES WHICH WEAKENS EARLY NEXT WEEK. RIDGING
ACROSS WESTERN CANADA IS SO AMPLIFIED THAT THERE IS ROOM FOR
ENERGY TO UNDERCUT IT ABOUT 20 DEGREES UNDER ITS APEX...IN THE MID
40S LATITUDE. THE MODELS AGREE WITH THESE IDEAS. THERE ARE
DIFFERENCES CONCERNING THE STRENGTH OF THE GREAT LAKES/NORTHEAST
TROUGHING WITH THE 00Z UKMET THE MOST AMPLIFIED AND THE 00Z/06Z
GFS THE QUICKEST TO LIFT THE CORE OF THE ENERGY NORTHWARD. THE
GFS/CANADIAN/ECMWF HAVE TRENDED STRONGER WITH THIS TROUGHING/MORE
AMPLIFIED WITH THE GENERAL FLOW PATTERN OVER THEIR PAST COUPLE
DAYS OF RUNS...WHICH ELIMINATED THE 06Z/12Z GFS FROM
CONSIDERATION. SINCE THE 00Z ECMWF/00Z CANADIAN SPLIT THE
DIFFERENCE EARLIER THIS MORNING...THEY WERE PREFERRED. SINCE
THEN...THE 12Z CANADIAN/12Z ECMWF SHIFTED NORTHWARD WITH THIS
VORTEX...AND THE CANADIAN QUICKENED THE PACE OF ITS TROUGH TOWARDS
THE GFS...WHICH INCREASES THE UNCERTAINTY IN THE FORECAST.
CONSIDERING THE TWO DAY TREND TOWARDS AMPLIFICATION...LET THE
MORNING PREFERENCE RIDE...THOUGH CONFIDENCE IS LESS THAN USUAL DUE
TO THESE CHANGES.
THE PROBLEM OF THE DAY CONTINUES TO BE A DEVELOPING TROPICAL
DISTURBANCE...NOW NEAR 22.5N 65.0W...WHICH CONTINUES TO EXHIBIT
DIFFERENCES AND DAY-TO-DAY CHANGES WITHIN THE MEDIUM RANGE
GUIDANCE. ALL THE GLOBAL GUIDANCE HAVE TRENDED WESTWARD WITH ITS
TRACK SINCE THIS TIME YESTERDAY WHILE THEIR FORWARD MOTION HAS
SHOWN GOOD CONTINUITY. HOWEVER...THE 00Z MULTI-MODEL ENSEMBLE
GUIDANCE SHOWS THE ECMWF MEMBERS MORE WEST/INLAND THAN THE
CANADIAN/GEFS MEMBERS WHICH ARE OFFSHORE. THE NON-ETA 03Z SREF
MEMBERS ALSO PREFER AN OFFSHORE TRACK WHILE THE ETA MEMBERS HEAD
THE POSSIBLE TROPICAL CYCLONE TOWARDS THE CAROLINAS. CHOSE TO
SPLIT THE DIFFERENCE IN THE ENSEMBLE SPREAD AND TRACK THE SYSTEM
CLOSE TO THE EASTERN SEABOARD...WHICH LED TO ADDITIONAL
ACCELERATION FROM THE NIGHT SHIFT PROGS. COORDINATION WITH NHC AT
16Z ALLOWED FOR EVEN GREATER ACCELERATION. THIS PREFERRED
SOLUTION IS CLOSEST TO THE 12Z NAM/12Z ECMWF/06Z DGEX WITH THIS
CYCLONE. HEAVY RAINFALL SHOULD SPREAD TO THE LEFT OF ITS TRACK
ALONG THE MID-ATLANTIC COAST THROUGH SOUTHERN AND EASTERN NEW
ENGLAND...IF THIS TRACK VERIFIES.
ROTH/JAMES
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