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Subtropical Storm NADINE


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SUBTROPICAL STORM NADINE DISCUSSION NUMBER  42
NWS NATIONAL HURRICANE CENTER MIAMI FL       AL142012
500 PM AST FRI SEP 21 2012
 
NADINE HAS UNDERGONE AN INTERESTING TRANSFORMATION DURING THE PAST
DAY OR SO.  WHILE CONVECTION HAS WEAKENED OVERALL...A BAND OF
MODERATE CONVECTION WRAPS AROUND THE EASTERN SEMICIRCLE OF THE
STORM.  AN UPPER-LEVEL LOW HAS ALSO DEVELOPED CLOSE TO THE CENTER
OF NADINE...A RESULT OF ALL OF THE MID-LATITUDE TROUGH INTERACTIONS
THAT THE CYCLONE HAS HAD RECENTLY.  THE STORM HAS A LARGER-THAN-
AVERAGE RADIUS OF MAXIMUM WINDS AND AN ASYMMETRIC WIND
DISTRIBUTION.  ALTHOUGH IT IS TEMPTING TO DECLARE NADINE
POST-TROPICAL WITH THE DECAYING CONVECTION...THE CYCLONE APPEARS TO
FIT MOST OF THE CHARACTERISTICS OF A SUBTROPICAL CYCLONE...ALBEIT
FROM AN UNUSUAL WAY OF GETTING THERE.  THE BEST ESTIMATE AT THIS
TIME IS THAT NADINE HAS BECOME SUBTROPICAL...WHICH IS SUPPORTED BY A
SUBTROPICAL CLASSIFICATION FROM TAFB.  THE INITIAL WIND SPEED
REMAINS 50 KT.  

NADINE IS MOVING TO THE SOUTH-SOUTHEAST AT ABOUT 10 KT.  THE CYCLONE
SHOULD GRADUALLY TURN TO THE SOUTHEAST AND EAST AS IT IS STEERED BY
A TROUGH OVER THE FAR NORTHEASTERN ATLANTIC OCEAN.  AFTER THE
TROUGH MOVES AWAY...HOWEVER...VERY LITTLE MOTION IS EXPECTED IN A
COUPLE DAYS TIME AS NADINE IS CAUGHT IN LIGHT STEERING CURRENTS. 
THE BULK OF THE GUIDANCE SUGGESTS THAT THE NEXT TROUGH IN ABOUT 5
DAYS WILL FINALLY CAUSE THE STORM TO MOVE A BIT FASTER TO THE
NORTHEAST AND LOSE ANY REMAINING TROPICAL CHARACTERSTICS.  THE NHC
FORECAST IS CLOSE TO A BLEND OF THE GFS...GEFS...ECMWF...FIM...AND
FLORIDA STATE SUPERENSEMBLES.  THIS RESULTS IN A MORE SOUTHWARD
TRACK EARLY ON...SMALL CHANGES IN THE MIDDLE OF THE FORECAST...AND
AN EASTWARD ADJUSTMENT TO THE PREVIOUS FORECAST AT DAY 5.  

THE INTENSITY FORECAST IS VERY CHALLENGING AND IS OF LOW CONFIDENCE. 
VERY COLD UPPER-LEVEL TEMPERATURES APPEAR TO BE SUPPORTING THE
CONVECTION NEAR THE CENTER IN COMBINATION WITH MARGINAL SSTS...
ALTHOUGH THE WATERS SHOULD BE WARMING WITH TIME.  MOST OF THE MODEL
GUIDANCE SUGGESTS LITTLE CHANGE IN STRENGTH OR A SLIGHTLY WEAKER
SYSTEM OVER THE NEXT COUPLE OF DAYS...AND THE OFFICIAL FORECAST IS
NEAR THE MODEL CONSENSUS.  IN A COUPLE OF DAYS...THE GFS AND ECMWF
MODELS BUILD AN UPPER-LEVEL ANTICYCLONE NEAR NADINE...WHICH COULD
FACILITATE A TRANSITION BACK TO A TROPICAL CYCLONE WHILE THE SYSTEM
IS OVER MARGINAL SSTS.  IT WOULD ALSO NOT BE SURPRISING IF IT
DECAYED INTO A POST-TROPICAL CYCLONE AT ANY TIME.
 
 
FORECAST POSITIONS AND MAX WINDS
 
INIT  21/2100Z 33.0N  27.0W   50 KT  60 MPH
 12H  22/0600Z 31.6N  26.5W   45 KT  50 MPH
 24H  22/1800Z 30.6N  25.8W   45 KT  50 MPH
 36H  23/0600Z 30.5N  25.0W   45 KT  50 MPH
 48H  23/1800Z 30.8N  24.7W   45 KT  50 MPH
 72H  24/1800Z 31.7N  25.0W   50 KT  60 MPH
 96H  25/1800Z 32.5N  24.5W   50 KT  60 MPH
120H  26/1800Z 32.5N  21.0W   50 KT  60 MPH...POST-TROPICAL
 
$$
FORECASTER BLAKE
 
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