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Post-Tropical Cyclone DEBBY


ZCZC MIATCDAT4 ALL
TTAA00 KNHC DDHHMM
 
POST-TROPICAL CYCLONE DEBBY DISCUSSION NUMBER  18
NWS NATIONAL HURRICANE CENTER MIAMI FL       AL042012
500 PM EDT WED JUN 27 2012
 
STRONG WESTERLY SHEAR AND DRY AIR CONTINUE TO TAKE A TOLL ON DEBBY.
ASCAT AMBIGUITY VECTORS FROM A 1527 UTC OVERPASS SUGGEST THAT THE
LOW-LEVEL CIRCULATION HAS BECOME ELONGATED TO THE POINT THAT IT IS
NOW A SHARP TROUGH AXIS WITHOUT A WELL DEFINED CENTER. IN
ADDITION...THE SYSTEM LACKS ENOUGH ORGANIZED DEEP CONVECTION TO BE
CLASSIFIABLE. ON THIS BASIS...DEBBY IS NOW DESIGNATED AS A POST-
TROPICAL CYCLONE. THE EARLIER ASCAT PASS HAD UNCONTAMINATED WINDS
TO 32 KT...AND NOAA BUOY 41010 HAD 1-MINUTE WINDS AS HIGH AS 31 KT.
IT IS ASSUMED THAT HIGHER WINDS COULD BE OCCURRING IN THE REMAINING
CONVECTION WELL REMOVED FROM THE CENTER...SO INTENSITY OF THE
SYSTEM IS ESTIMATED TO BE 35 KT.
 
BASED UPON RECENT SATELLITE FIXES...THE INITIAL MOTION ESTIMATE IS
095/11...ALTHOUGH THIS IS DIFFICULT TO DETERMINE PRECISELY DUE TO
THE POOR DEFINITION OF THE CENTER. DEBBY SHOULD BE STEERED BY THE
FLOW ON THE SOUTH SIDE OF A DEEP TROUGH COVERING THE WESTERN
ATLANTIC...EVEN AS THIS WEATHER SYSTEM BEGINS TO LIFT OUT. ONCE
REACHING A HIGHER LATITUDE...DEBBY IS EXPECTED TO FEEL THE
INFLUENCE OF THE MID-LATITUDE WESTERLY FLOW AND ACCELERATE
NORTHEASTWARD DURING THE REMAINDER OF THE FORECAST PERIOD. GLOBAL
MODELS ARE IN GOOD AGREEMENT ON THIS SCENARIO BUT STILL DIFFER ON
THE TIMING ASPECTS OF THE FORECAST. THE GFS IS SUBSTANTIALLY SLOWER
THAN THE ECMWF/UKMET SINCE ITS MORE SOUTHERN INITIAL HEADING KEEPS
IT EQUATORWARD OF THE STRONGER WESTERLY FLOW. THE NEW TRACK
FORECAST IS SLOWED A BIT TO ACCOUNT FOR THIS POSSIBILITY...BUT IS
ESSENTIALLY SIMILAR TO THE PREVIOUS ONE.
 
LARGE-SCALE MODELS CONTINUE TO SHOW A RELATIVE DECREASE IN THE SHEAR
OVER DEBBY AS IT TRAVERSES THE CENTRAL ATLANTIC OVER THE NEXT DAY
OR TWO. ALTHOUGH AN ABUNDANCE OF VERY DRY AND STABLE AIR OVER THIS
REGION AND DECREASING SEA SURFACE TEMPERATURES COULD BE FACTORS
THAT PREVENT DEBBY FROM REGENERATING AS A TROPICAL CYCLONE...GLOBAL
MODELS CONTINUE TO INDICATE THIS TO BE A POSSIBILITY. THE OFFICIAL
NHC FORECAST CARRIES DEBBY AS A POST- TROPICAL CYCLONE THROUGHOUT
THE FORECAST PERIOD...THOUGH DEBBY COULD REACQUIRE TROPICAL
CHARACTERISTICS AT SOME POINT.
 
 
FORECAST POSITIONS AND MAX WINDS
 
INIT  27/2100Z 29.5N  78.3W   35 KT  40 MPH...POST-TROPICAL
 12H  28/0600Z 29.4N  76.5W   35 KT  40 MPH...POST-TROPICAL
 24H  28/1800Z 29.7N  73.8W   35 KT  40 MPH...POST-TROPICAL
 36H  29/0600Z 30.7N  71.0W   35 KT  40 MPH...POST-TROPICAL
 48H  29/1800Z 32.1N  68.5W   35 KT  40 MPH...POST-TROPICAL
 72H  30/1800Z 35.7N  64.2W   35 KT  40 MPH...POST-TROPICAL
 96H  01/1800Z 40.0N  59.0W   40 KT  45 MPH...POST-TROPICAL
120H  02/1800Z 46.0N  48.0W   40 KT  45 MPH...POST-TROPICAL
 
$$
FORECASTER KIMBERLAIN
 
NNNN


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Page last modified: Monday, 31-Dec-2012 12:09:12 UTC