923
FXUS02 KWBC 301818
PMDEPD
EXTENDED FORECAST DISCUSSION
NWS HYDROMETEOROLOGICAL PREDICTION CENTER CAMP SPRINGS MD
217 PM EDT SAT AUG 30 2008
VALID 12Z TUE SEP 02 2008 - 12Z SAT SEP 06 2008
..TWO TROPICAL SYSTEMS IMPACTING U.S. WEATHER THIS PERIOD
OVERALL MID LATITUDE FLOW IS IN GOOD AGREEMENT THIS PERIOD WITH AN
AMPLIFYING TROF DIVING INTO THE GREAT BASIN WITH A LEAD SHORTWAVE
EJECTING NEWD THRU THE DAKOTAS. FOLLOWING SHORTWAVE RELOADS THE
TROF WITH 00Z ECMWF DROPPING THE MOST ENERGY IN AND SLOWING ITS
EWD PROGRESS DAYS 6 AND 7. EWD ALL MODELS DEVELOP STRONG MID LEVEL
RIDGING OVER ERN CONUS TUES AND WED WITH ITS AXIS SHIFTING EWD
OVER THE MID ATLC STATES REGION AND ADJACENT ATLC. WHILE THE
OVERALL PATTERN IS SIMILAR THERE ARE ENOUGH DETAIL DIFFERENCES TO
IMPACT THE TRACKS OF TROPICAL SYSTEMS GUSTAV AND HANNA MAINLY MID
AND LATE PERIOD.
CMC AND ECMWF ALLOW THE INFLUENCE OF THE APPROACHING SHORTWAVE
TROF TO PICK UP GUSTAV AND EJECT IT RAPIDLY NEWD UP THE MS VALLEY
TOWARDS THE GREAT LAKES REGION. OP RUNS OF RECENT 00Z/06Z GFS
LEAVE THIS BYPASSED IN E TX OR EVEN ALONG THE TX COAST AS DOES
UKMET AND A LARGE NUMBER OF GFS ENS MEANS AND ENOUGH TO PERTURB
THE GFS ENS MEAN TO LEAVE LOW PRESSURE IN THE NW GLFMEX. DUE TO
THE UNCERTAINTY THE HPC PREFERNCE IS TOWARDS A NE EJECTION AS
USUALLY HAPPENS BUT SLOWER THAN CMC AND ECMWF CLOSER TO THE ECMWF
ENS MEAN. THIS IS A NEWD EJECTION ALONG A STATIONARY BOUNDARY FROM
NE TX ACROSS AR AND UP THE LOWER OH VALLEY.
SEE NHC FORECASTS/DISCUSSIONS FOR HURCN GUSTAV.
EWD T.S.HANNA FORECAST TO BECOME A HURCN AND THEN WEAKEN TO STRONG
TS WITH MUCH INTENSITY FORECAST SPREAD. ALL GUIDANCE TAKES THIS
NWD AND THEN WWD WITH HURCN MODEL GUIDANCE THEN BECOMING MORE
ERRATIC AT DAY 5 WED-THU. GLOBAL DYNAMICAL MODELS HAVE BEEN MUCH
MORE CONSISTENT AND IN FAIRLY GOOD AGREEMENT ON ITS SW TRACK INTO
THE BAHAMAS BY DAY 5. ITS FUTURE DEPENDS MUCH UPON HOW MUCH
RIDGING BUILDS IN NORTH OF THE SYSTEM ACROSS THE MID ATLC STATES
AND ADJACENT ATLC AS THE RIDGING REPLACES AN EXITING MID LEVEL LOW
OFF THE MARITIMES.
CMC/GFS AND ECMWF AND ITS ENS MEAN HOLD ONTO THE RIDGE AND MOVE
HANNA AROUND ITS WEST PERIPHERY. BIGGEST QUESTION IS WHERE WILL
HANNA BE AS THE MID LEVEL EVOLVES. 00Z/06Z GFS/NOGAPS AND GFS ENS
MEAN GAIN THE HIGHEST LATITUDE IN THE BAHAMAS WITH HANNA ALLOWING
FOR A FUTURE DAYS 6 AND 7 TRACK MUCH MORE EWD TAKING HANNA INTO
THE SOUTHEAST COAST DAYS 6/7 AS DOES DGEX. CMC AND ECMWF START OUT
FROM DAY 5 AT LOWER LATITUDES AND MAKE THE NW AND N TURN ALONG THE
WEST COAST OF FL OR ERN GLFMEX. UKMET GOES THE FARTHEST SOUTH WITH
THIS SYSTEM ON THE SOUTH SIDE OF CUBA BY DAY 5. PREVIOUS YEARS THE
UKMET WAS ONE OF THE BETTER MODELS IN THE CARRIBEAN AND WRN ATLC
IF ONE ADJUSTED ITS LATITUDE SEVERAL DEGREES NWD. MAKING THIS
ADJUSTMENT WOULD PUT IT INTO THE ECMWF/CMC CAMP. BEGINNING FROM
THE TPC DAY 5 POSITION WHICH IS IN THE MIDDLE OF THE GROUPING..HPC
PREFERENCE WOULD BE AN ECMWF ENS MEAN AND PROGS HAVE BEEN ADJUSTED
FOR THIS FOR DAYS 6 AND 7 FRI/SAT. THIS IS WITHIN THE SPREAD
ENVELOPE ON THE WEST SIDE TAKING HANNA FROM THE FL STRAITS FRI
ALONG THE WEST FL COAST TO NEAR APALACHEE BAY SAT. THIS SOLUTION
IS ALSO SLOWER THAN ALL OP MODELS BUT IN LATITUDINAL AGREEMENT OF
BOTH GFS AND ECMWF ENS MEANS. SEE TPC
FORCASTS/ADVISORIES/DISCUSSION OF HANNA.
HPC UPDATED PRELIM PROGS USED A MAJORITY OF THE ECMWF MEAN WITH
SOME 06Z GFS TO GENERATE PROGS. MANUAL ADJUSTMENTS MADE FOR GUSTAV
AND HANNA.
AFTN MODEL RUNS...
GFS SIMILAR TO ITS PRIOR 00Z RUN OVERALL BUT A TREND TOWARDS
PICKING UP THE REMAINS OF GUSTAV ALTHOUGH STILL NOT TO THE EXTENT
OF 00Z ECMWF AND CMC. HANDLING OF HANNA STILL CRITICAL MAINLY WITH
ITS TROPICAL HANDLING OF THE CENTER BRINGING FARTHER NWD OFF THE
EAST COAST OF FLORIDA ALLOWING FOR IT TO ROUND THE WRN EDGE OF THE
MID LEVEL HIGH AND TAKES IT INTO THE SC COAST BY DAY 6 ABOUT 18
HRS FASTER THAN THE 00Z RUN. THE MID LEVEL TROF AXIS BY DAY 6 FRI
IS MUCH MORE ORIENTED NE-SW FROM SRN MANITOBA TO THE FOUR CORNERS
REGION LOOKING MUCH MORE LIKE THE ECMWF AN ECMWF ENS MEAN.
CMC
BY DAY 6 CMC MID LEVEL TROF IS SIMILAR TO AND SOMEWHAT SLOWER THAN
THE 12Z GFS/ 00Z ECMWF ENS MEAN AND 00Z GFS ENS MEAN ACROSS THE
NRN HIGH PLAINS. EWD ITS MOVEMENT OF HANNA DOES NOT GET AS FAR
WEST INTO THE FL STRAIT BEFORE BEING PULLED NORTH ALONG/OFF THE
EAST COAST OF FLORIDA WITH IMPLICATIONS FOR SC/NC.
UKMET
MID LEVEL FLOW CLOSE TO OTHER MODELS BUT A CONTINUED MORE SRLY
TRACK OF HANNA CONSISTENT WITH ITS PRIOR RUNS TAKING THE LOW SOUTH
OF CUBA.
AFTN UPDATED HPC FINALS...SOME CHANGES TO POSITIONS OF REMNANTS OF
GUSTAV. ELSW NO CHANGES TO EARLIER PRELIMS.
ROSENSTEIN
ROSENSTEIN
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