Tropical Storm NADINE

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TROPICAL STORM NADINE DISCUSSION NUMBER  23
NWS NATIONAL HURRICANE CENTER MIAMI FL       AL142012
1100 PM AST SUN SEP 16 2012
 
THE SATELLITE PRESENTATION OF NADINE HAS DEGRADED SINCE THIS
AFTERNOON WITH LESS CONVECTION NEAR THE CENTER AND A MORE
ASYMMETRIC APPEARANCE.  RECENT MICROWAVE IMAGES ALSO SHOW THAT THE
LOW-LEVEL CENTER IS DISPLACED TO THE SOUTHWEST OF THE PRIMARY
CONVECTIVE BAND.  AS A RESULT...DVORAK T-NUMBERS HAVE DECREASED AND
THE INITIAL INTENSITY IS LOWERED TO 60 KT...WHICH IS A BLEND OF 
THE LATEST AND T- AND CI-NUMBERS.  ALTHOUGH VERTICAL SHEAR IS
FORECAST TO DECREASE A LITTLE DURING THE NEXT DAY OR SO...IT IS
EXPECTED TO REMAIN MODERATE TO STRONG OVER THE NEXT 72 HOURS.
THE SHEAR ALONG WITH GRADUALLY DECREASING SSTS SHOULD INDUCE SOME
WEAKENING...HOWEVER MUCH OF THE INTENSITY GUIDANCE AND THE GLOBAL
MODELS SHOW LITTLE OVERALL CHANGE IN STRENGTH OVER THE NEXT COUPLE
OF DAYS.  THE LACK OF WEAKENING COULD BE DUE TO THE INTERACTION OF
NADINE AND A SHORT-WAVE TROUGH APPROACHING THE CYCLONE FROM THE
WEST.  THE NHC FORECAST IS IN GOOD AGREEMENT WITH THE GUIDANCE AND
ONLY PREDICTS A SLIGHT DECREASE IN INTENSITY DURING THE NEXT
SEVERAL DAYS. 
 
MICROWAVE DATA DURING THE PAST 6-12 HOURS SUGGESTS THAT NADINE
IS BEGINNING TO SLOW DOWN AND HAS TURNED EAST-NORTHEASTWARD.  THE
INITIAL MOTION ESTIMATE IS 075/16 KT.  AN ADDITIONAL REDUCTION IN
FORWARD SPEED AND A TURN TOWARD THE NORTHEAST ARE EXPECTED DURING
THE NEXT DAY OR TWO AS A MID-LEVEL RIDGE SLIDES EASTWARD TO THE
NORTH OF NADINE AND A CUT-OFF LOW FORMS TO THE WEST OF THE CYCLONE.
THE MODEL GUIDANCE IS IN GOOD AGREEMENT DURING THE FIRST 2 TO 3 DAYS
OF THE FORECAST PERIOD.  AFTER THAT TIME...ANOTHER MID- TO
UPPER-LEVEL LOW IS FORECAST TO MOVE SOUTHWARD OVER THE NORTHEASTERN
ATLANTIC.  AS THIS OCCURS...THE TRACK GUIDANCE BECOME QUITE
DIVERGENT AS THEY DEPICT VARYING INTERACTIONS OF NADINE AND THE
UPPER-LOW.  GIVEN THE LARGE SPREAD IN THE GUIDANCE...THE NHC
FORECAST REMAINS NEAR THE MODEL CONSENSUS AT DAYS 4 AND 5. 

ALTHOUGH NADINE HAS RECENTLY TAKEN ON A LESS TROPICAL APPEARANCE IN
SATELLITE DUE TO AN APPROACHING TROUGH...THE GLOBAL MODELS SUGGEST
THIS TROUGH WILL NOT BE STRONG ENOUGH TO CAUSE NADINE TO TRANSITION
INTO AN EXTRATROPICAL CYCLONE.  INSTEAD...THE GFS AND ECMWF
INDICATE THAT AS THE TROPICAL CYCLONE INTERACTS WITH THE CUT-OFF
LOW IN A FEW DAYS...NADINE WILL THEN TRANSITION INTO AN
EXTRATROPICAL CYCLONE...AND THIS TRANSFORMATION IS FORECAST TO 
BE COMPLETE IN ABOUT 5 DAYS.  
 
FORECAST POSITIONS AND MAX WINDS
 
INIT  17/0300Z 31.4N  38.1W   60 KT  70 MPH
 12H  17/1200Z 32.1N  35.8W   55 KT  65 MPH
 24H  18/0000Z 33.2N  33.9W   55 KT  65 MPH
 36H  18/1200Z 34.4N  32.9W   55 KT  65 MPH
 48H  19/0000Z 35.6N  32.5W   55 KT  65 MPH
 72H  20/0000Z 37.0N  31.5W   50 KT  60 MPH
 96H  21/0000Z 37.5N  29.5W   50 KT  60 MPH
120H  22/0000Z 37.5N  28.5W   50 KT  60 MPH...POST-TROP/EXTRATROP
 
$$
FORECASTER BROWN
 
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