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Tropical Storm NADINE (Text)

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TROPICAL STORM NADINE DISCUSSION NUMBER  61
NWS NATIONAL HURRICANE CENTER MIAMI FL       AL142012
500 PM AST THU SEP 27 2012

THE CONVECTION ASSOCIATED WITH NADINE HAS CHANGED FROM RAGGED TO
WRAPPED-UP THIS AFTERNOON...WITH FORMATION OF A WELL-DEFINED
CENTRAL DENSE OVERCAST AND AN EARLIER ATTEMPT AT EYE FORMATION. 
SATELLITE INTENSITY ESTIMATES FROM TAFB AND SAB HAVE INCREASED TO
55 KT...AND THAT IS THE INITIAL INTENSITY.  THIS COULD BE A LITTLE
CONSERVATIVE...AS RECENT AMSU INTENSITY ESTIMATES FROM CIMSS AND
CIRA HAVE BEEN 55-65 KT.  THE CIRRUS OUTFLOW IS FAIR IN THE
NORTHEASTERN SEMICIRCLE...BUT IT IS RESTRICTED IN THE SOUTHWESTERN
SEMICIRCLE WHERE THERE ARE SIGNS OF INCREASING VERTICAL WIND SHEAR.
 
THE INITIAL MOTION IS NOW 255/6.  NADINE IS ON THE SOUTH SIDE
OF A DEEP-LAYER RIDGE...WHICH IS FORECAST TO MOVE EASTWARD DURING
THE NEXT 48-72 HR.  THIS WILL ALLOW NADINE TO TURN NORTHWESTWARD
AND NORTHWARD AS IT MOVES BETWEEN THE RIDGE AND A MID/UPPER-LEVEL
LOW SEEN IN WATER VAPOR IMAGERY NEAR 30N48W.  AFTER 72 HR...THE
TRACK GUIDANCE REMAINS CONSISTENT IN ITS DIVERGENCE.  THE GFS...GFS
ENSEMBLE MEAN...GFDL...AND HWRF FORECAST NADINE TO MOVE SLOWLY
EASTWARD TO NORTHEASTWARD ALONG THE SOUTHERN EDGE OF THE WESTERLIES
AS A TROUGH PASSES NORTH OF THE STORM.  THE UKMET...ECMWF...
CANADIAN...AND NOGAPS FORECAST A RIDGE TO BUILD NORTH AND NORTHWEST
OF NADINE IN THE WAKE OF THE WESTERLY TROUGH...WHICH WOULD STEER
THE STORM BACK TOWARD THE SOUTH OR SOUTHWEST.  SINCE THERE IS
LITTLE CHANGE TO THE TRACK GUIDANCE SINCE THE LAST ADVISORY...THE
NEW FORECAST TRACK IS AN UPDATE OF THE PREVIOUS FORECAST...WITH A
FORECAST SLOW MOTION AFTER 72 HR.
 
THE GLOBAL MODELS FORECAST NADINE TO INTERACT WITH THE
MID/UPPER-LEVEL LOW NEAR 30N48W DURING THE FORECAST PERIOD...WITH
THE TWO SYSTEMS POSSIBLY MERGING BY 96-120 HR.  IN ADDITION...SMALL
SHORTWAVE TROUGHS ROTATING AROUND THE LOW COULD ALSO INTERACT WITH
THE STORM.  WHILE IT IS EXPECTED THAT NADINE WILL ENCOUNTER
INCREASING SHEAR...IT IS POSSIBLE THAT THE SHORTWAVE TROUGHS COULD
PARTLY SHIELD THE STORM...AS WELL AS PROVIDE UPPER-LEVEL DIVERGENCE
THAT COULD ALLOW STRENGTHENING.  THE INTENSITY GUIDANCE IS IN FAIR
AGREEMENT ON FORECASTING A LITTLE MORE INTENSIFICATION BEFORE
NADINE REACHES COOLER SEA SURFACE TEMPERATURES IN ABOUT 36 HR.  THE
NEW INTENSITY FORECAST DOES LIKEWISE AND IS NOW CLOSE TO THE
SHIPS...LGEM...AND INTENSITY CONSENSUS MODELS.  HOWEVER...THIS IS A
LOW CONFIDENCE FORECAST DUE TO THE UNCERTAINTY IN HOW MUCH SHEAR
NADINE COULD ENCOUNTER.
 
 
FORECAST POSITIONS AND MAX WINDS
 
INIT  27/2100Z 28.6N  32.8W   55 KT  65 MPH
 12H  28/0600Z 28.8N  33.8W   60 KT  70 MPH
 24H  28/1800Z 29.7N  34.8W   60 KT  70 MPH
 36H  29/0600Z 31.2N  35.5W   60 KT  70 MPH
 48H  29/1800Z 32.9N  36.1W   60 KT  70 MPH
 72H  30/1800Z 35.5N  37.0W   55 KT  65 MPH
 96H  01/1800Z 36.0N  37.0W   50 KT  60 MPH
120H  02/1800Z 36.5N  37.0W   45 KT  50 MPH
 
$$
FORECASTER BEVEN
 
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