MODEL DIAGNOSTIC DISCUSSION
NWS HYDROMETEOROLOGICAL PREDICTION CENTER CAMP SPRINGS MD
121 PM EDT SAT SEP 29 2007

VALID SEP 29/1200 UTC THRU OCT 03/0000 UTC

MODEL TRENDS...
...DEEP CYCLONE/POSSIBLY SUBTROPICAL LOW RETROGRADING ACROSS
FLORIDA...
THE NAM HAS TRENDED DEEPER/MORE RETROGRESSIVE WITH THIS SYSTEM
OVER ITS PAST DAY OF RUNS...PARTIALLY DUE TO STRONGER RIDGING NEAR
THE NORTH CAROLINA/VIRGINIA BORDER. THE ECMWF HAS TRENDED MORE
SOUTHWEST WITH THIS SYSTEM OVER ITS PAST COUPLE DAYS OF RUNS DUE
TO STRONGER RIDGING OVER THE MID-ATLANTIC STATES. THE GFS HAS BEEN
CONSISTENT IN KEEPING MOST OF THE ENERGY WITHIN THE TROUGH WEST OF
BERMUDA WHICH THEN RECURVES NORTHEASTWARD...ALLOWING A MUCH WEAKER
PIECE OF ENERGY TO RETROGRADE THROUGH THE SOUTHERN GULF OF MEXICO.

MODEL DIFFERENCES AND PREFERENCES...
...DEEP CYCLONE/POSSIBLY SUBTROPICAL LOW RETROGRADING ACROSS
FLORIDA...
NORMALLY...WHEN A MERIDIONAL RIDGE REORIENTS ON A MORE EAST-WEST
AXIS...A CLOSED CYCLONE WILL EMERGE FROM THE BASE OF THE PREVIOUS
TROUGH UNDER THE RIDGE AND RETROGRADE. THE
CANADIAN...NAM...ECMWF...AND UKMET SHOW THIS IDEA. THE GFS ALLOWS
A BULK OF THE ENERGY TO BE INITIALLY TRAPPED NEAR THE COL POINT IN
THE UPPER PATTERN BEFORE LIFTING NORTHEAST AHEAD OF THE NEXT
SHORTWAVE. WILL REJECT THE GFS SOLUTION AS IT DOES NOT FIT THE
ABOVE THINKING. THE CANADIAN IS NOT MUCH BETTER...ALLOWING A
SHORTWAVE TO INDUCE A MODERATELY STRONG SURFACE LOW THAT THEN
TRACKS TOWARDS THE CAROLINAS. SINCE THE BULK OF THE ENERGY SHOULD
BE RETROGRADING THROUGH THE FLORIDA KEYS INTO THE SOUTHEAST GULF
OF MEXICO...THINK THIS CYCLONE IS TOO DEEP AND TOO FAR REMOVED
FROM WHERE THE UPPER CENTER IS EXPECTED TO BE. THE UKMET COUPLES
THIS SYSTEM IS AS FAR WEST AS THE WEAK 12Z GFS...BUT WITH A DEEPER
CENTRAL PRESSURE. THE FORECAST GUIDANCE TENDS TO RETROGRADE CLOSED
CYCLONES IN THE SUBTROPICS TOO QUICKLY. SO...FOR NOW...WILL FAVOR
THE ECMWF SOLUTION BASED ON THE ABOVE REASONING.

MODEL DIAGNOSTIC DISCUSSION

edit: This probably should have been posted in the Forecast Lounge. Since the future system is currently impacting the FL East Coast, to a degree. I'll leave the decision to move it up to MikeC and ED.~danielw