PRELIMINARY EXTENDED FORECAST DISCUSSION
NWS HYDROMETEOROLOGICAL PREDICTION CENTER CAMP SPRINGS MD
926 AM EDT SAT AUG 30 2008

...TWO TROPICAL SYSTEMS IMPACTING U.S. WEATHER THIS PERIOD...

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.

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.

The HPC has the hard task of giving 7 day forcasts. They were the first to predict the Fay stall. They are only concerned with the general area that will be impacted (like Florida or southeast) not the precise location of landfall. But, over the years have found their information usefull for longer range planning.