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Tropical Storm NADINE


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TROPICAL STORM NADINE DISCUSSION NUMBER  57
NWS NATIONAL HURRICANE CENTER MIAMI FL       AL142012
500 PM AST WED SEP 26 2012

NADINE CONTINUES TO PRODUCE ORGANIZED CONVECTIVE BANDING...NOW
PRIMARILY OVER THE SOUTHWESTERN SEMICIRCLE.  AN EARLIER OSCAT
OVERPASS SHOWED 40 KT WINDS IN THE NORTHWESTERN QUADRANT...AND THE
SATELLITE INTENSITY ESTIMATED FROM TAFB HAS INCREASED TO 45 KT. 
BASED ON THESE...THE INITIAL INTENSITY REMAINS 45 KT.  NADINE IS
PRODUCING GOOD CIRRUS OUTFLOW IN ALL DIRECTIONS EXCEPT FOR THE
SOUTHEAST.  HOWEVER...DROPSONDES FROM THE NASA GLOBAL HAWK AIRCRAFT
NORTH OF NADINE SHOW 35-40 KT NORTHERLY WINDS ADVECTING DRY AIR
TOWARD THE STORM.  LATER DROPSONDES SHOULD HELP DETERMINE HOW MUCH
OF THESE WINDS/DRY AIR ARE ACTUALLY REACHING THE CORE OF NADINE.

THE INITIAL MOTION IS NOW 200/4.  THE TRACK GUIDANCE REMAINS IN GOOD
AGREEMENT FOR THE NEXT 48-72 HR...FORECASTING NADINE TO TURN
SOUTHWESTWARD...WESTWARD...AND THEN NORTHWESTWARD AROUND A
DEEP-LAYER RIDGE MOVING EASTWARD ACROSS THE NORTHEASTERN ATLANTIC.
THE GUIDANCE AGAIN BECOMES VERY DIVERGENT AFTER 72 HR.  WHILE THE
MODELS NOW AGREE THAT NADINE WILL NOT RECURVE AHEAD OF A
MID/UPPER-LEVEL TROUGH...THERE CONTINUE TO BE MAJOR DIFFERENCES IN
THE DIRECTION OF MOTION AFTER 96 HR.  THE GFDL...GFS...AND GFS
ENSEMBLE MEAN SHOW A SLOW MOTION TOWARD THE EAST OR NORTHEAST.  THE
ECMWF...UKMET...AND NOGAPS SHOW A TURN TOWARD THE WEST OR SOUTHWEST
DUE TO RIDGING IN THE WAKE OF THE TROUGH.  FINALLY...THE HWRF AND
THE CANADIAN SHOW LITTLE MOTION.  THE NEW FORECAST TRACK HAS MINOR
ADJUSTMENTS DURING THE FIRST 48 HR...AND THEN IS SIMILAR TO THE
PREVIOUS FORECAST THEREAFTER.  GIVEN THE MODEL SPREAD AFTER 96
HR...THE NEW FORECAST IS FOR A VERY SLOW MOTION DURING THIS TIME. 
THE NEW TRACK REMAINS NEAR THE CENTER OF THE GUIDANCE ENVELOPE.

THE INTENSITY FORECAST IS UNCERTAIN DUE TO A COMPLICATED UPPER-LEVEL
WIND PATTERN NEAR NADINE.  FIRST IS THE 400 MB NORTHERLY WINDS
MENTIONED ABOVE AND THEIR POSSIBLE IMPACT ON THE STORM.  SECOND...
WATER VAPOR IMAGERY SHOWS AN UPPER-LEVEL LOW NEAR 29N47W...WITH A
TROUGH EXTENDING EASTWARD TO JUST SOUTH OF NADINE.  STRONG UPPER-
LEVEL WESTERLY WINDS ARE OCCURRING JUST SOUTH OF THE TROUGH...BUT
ARE CURRENTLY NOT AFFECTING THE TROPICAL CYCLONE.  THE GLOBAL
MODELS ALL FORECAST INCREASING UPPER-LEVEL WINDS NEAR NADINE AFTER
36 HR.  HOWEVER...THEY ALL SHOW THAT THE UPPER-LEVEL TROUGH COULD
CONTINUE TO SHELTER NADINE FROM THE WORST OF THE SHEAR. FINALLY...
MOST OF THE GLOBAL MODELS SHOW NADINE MERGING WITH THE UPPER-LEVEL
LOW BY 120 HR...WHICH COULD CHANGE THE STRUCTURE OF THE CYCLONE. 
PROBABLY THE LEAST COMPLICATED PART OF THIS FORECAST IS THAT NADINE
SHOULD MOVE OVER COOLER SEA SURFACE TEMPERATURES AFTER 36 HR.  THE
INTENSITY GUIDANCE GENERALLY SHOWS SLOW STRENGTHENING THROUGH 48-72
HR.  DUE TO THE POSSIBILITY THAT SHEAR AND DRY AIR WILL AFFECT
NADINE...THE INTENSITY FORECAST CALLS FOR A SHORTER WINDOW FOR
STRENGTHENING...WITH A PEAK INTENSITY IN 24-36 HR.  IT ALSO CALLS
FOR LESS INTENSIFICATION THAN THE SHIPS...LGEM...AND INTENSITY
CONSENSUS MODELS.
 
 
FORECAST POSITIONS AND MAX WINDS
 
INIT  26/2100Z 30.2N  30.8W   45 KT  50 MPH
 12H  27/0600Z 29.4N  31.5W   45 KT  50 MPH
 24H  27/1800Z 28.8N  32.8W   50 KT  60 MPH
 36H  28/0600Z 29.0N  34.2W   50 KT  60 MPH
 48H  28/1800Z 29.7N  35.3W   50 KT  60 MPH
 72H  29/1800Z 32.5N  36.5W   50 KT  60 MPH
 96H  30/1800Z 35.5N  37.0W   45 KT  50 MPH
120H  01/1800Z 36.0N  37.0W   45 KT  50 MPH
 
$$
FORECASTER BEVEN
 
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