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Hurricane NADINE (Text)

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HURRICANE NADINE DISCUSSION NUMBER  20
NWS NATIONAL HURRICANE CENTER MIAMI FL       AL142012
500 AM AST SUN SEP 16 2012

NADINE LOOKS A LITTLE RAGGED IN SATELLITE IMAGERY THIS MORNING...AS
THE CENTRAL CONVECTION LOOKS MORE SHEARED THAN IT DID EARLIER.  AN
AMSU OVERPASS AT 0448 UTC SUGGESTS THAT THE SYSTEM REMAINS TILTED
VERTICALLY...WITH THE MID-LEVEL CENTER DISPLACED EAST OF THE
LOW-LEVEL CENTER DUE TO 25 KT OF WESTERLY VERTICAL WIND SHEAR. 
SATELLITE INTENSITY ESTIMATES ARE 77 KT FROM SAB AND 65 KT FROM
TAFB...AND AN AMSU-BASED INTENSITY ESTIMATE FROM CIMSS IS 72 KT. 
BASED ON THESE DATA...THE INITIAL INTENSITY REMAINS 70 KT.

THE INITIAL MOTION REMAINS 095/15.  NADINE IS EMBEDDED IN
MID-/UPPER-LEVEL WESTERLY FLOW THAT SHOULD CONTINUE TO STEER THE
CYCLONE EASTWARD FOR THE NEXT 12-24 HR.  AFTER THAT TIME...THE
GLOBAL MODELS AGREE ON THE FORMATION OF A DEEP-LAYER LOW WEST OF
NADINE...WHICH SHOULD CAUSE THE CYCLONE TO TURN NORTHEASTWARD. 
NEAR THE END OF THE FORECAST PERIOD...THE MODELS DIVERGE ON THE
INTERACTION OF NADINE WITH AN MID-/UPPER-LEVEL LOW OVER THE
NORTHEASTERN ATLANTIC.  THE ECMWF...CANADIAN...AND NOGAPS SHOW
NADINE TRYING TO MERGE WITH THIS LOW.  THE GFS DOES NOT SHOW A
MERGER AND TRAPS NADINE SOUTH OF A BUILDING RIDGE.  THE UKMET SHOWS
THE LOW MOVING FARTHER EAST THAN THE ECMWF/CANADIAN/NOGAPS...AND AS
A RESULT...FORECASTS NADINE TO MOVE MUCH FARTHER TO THE EAST THAN
THE OTHER MODELS.  GIVEN THE UNCERTAINTY AND THE SPREAD IN THE
TRACK GUIDANCE BY 120 HR...THE NEW TRACK FORECAST FOLLOWS THE
PREVIOUS FORECAST IN SHOWING A SLOW MOTION.  OVERALL...THE NEW
TRACK FORECAST IS SIMILAR TO THE PREVIOUS FORECAST AND LIES NEAR
THE CENTER OF THE TRACK GUIDANCE ENVELOPE.

THE INTENSITY FORECAST IS FULL OF ISSUES.  THE FIRST IS THE WESTERLY
SHEAR...WHICH LIKELY SHOULD CONTINUE FOR THE NEXT 24 HR AND COULD
CAUSE WEAKENING.  THE SECOND IS THAT THE GLOBAL MODELS FORECAST TWO
UPPER-LEVEL SHORTWAVE TROUGHS WEST OF NADINE TO OVERTAKE THE
HURRICANE BETWEEN 24-72 HR.  THIS COULD DECREASE THE SHEAR...
PROVIDE AN IMPROVED OUTFLOW...AND PERMIT SOME INTENSIFICATION.  THE
THIRD IS THE POSSIBILITY OF A MERGER WITH THE UPPER-LEVEL LOW NEAR
120 HR...WHICH...IF IT OCCURS...WOULD SIGNIFICANTLY CHANGE THE
STRUCTURE OF NADINE.  FINALLY...THE FORECAST TRACK TAKES THE
CYCLONE OVER DECREASING SEA SURFACE TEMPERATURES.  DESPITE THIS
COMPLEXITY...THE INTENSITY GUIDANCE IS IN RELATIVELY GOOD AGREEMENT
THAT NADINE SHOULD CHANGE LITTLE IN STRENGTH DURING THE NEXT 48
HR...FOLLOWED BY A SLOW WEAKENING.  THE NEW INTENSITY FORECAST
FOLLOWS THAT SCENARIO AND IS UNCHANGED FROM THE PREVIOUS FORECAST. 
IT IS ALSO IN GOOD AGREEMENT WITH THE SHIPS...LGEM...AND THE
INTENSITY CONSENSUS.  
 
FORECAST POSITIONS AND MAX WINDS
 
INIT  16/0900Z 30.5N  44.7W   70 KT  80 MPH
 12H  16/1800Z 30.5N  42.0W   70 KT  80 MPH
 24H  17/0600Z 31.3N  38.6W   70 KT  80 MPH
 36H  17/1800Z 32.3N  36.0W   65 KT  75 MPH
 48H  18/0600Z 33.5N  34.3W   65 KT  75 MPH
 72H  19/0600Z 36.0N  32.5W   60 KT  70 MPH
 96H  20/0600Z 36.5N  32.0W   55 KT  65 MPH
120H  21/0600Z 36.5N  31.5W   50 KT  60 MPH
 
$$
FORECASTER BEVEN
 
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