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Hurricane NADINE


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HURRICANE NADINE DISCUSSION NUMBER  68
NWS NATIONAL HURRICANE CENTER MIAMI FL       AL142012
1100 AM AST SAT SEP 29 2012

ALTHOUGH ANALYSES FROM CIMSS AND THE SHIPS MODEL CONTINUE TO SHOW 20
KT OF SOUTHWESTERLY VERTICAL WIND SHEAR...NADINE HAS BECOME BETTER
ORGANIZED DURING THE PAST SEVERAL HOURS.  AN EYE HAS RE-APPEARED IN
VISIBLE IMAGERY...AND AN SSM/IS OVERPASS AT 1112 UTC SHOWED THAT
THE LOW- AND MID-LEVEL CENTERS ARE NOW MORE VERTICALLY ALIGNED. 
SATELLITE INTENSITY ESTIMATES FROM TAFB AND SAB ARE 65 KT. 
ALSO...CIMSS ADT ESTIMATES ARE NEAR 80 KT...AND A RECENT CIMSS AMSU
ESTIMATE IS 64 KT.  BASED ON THESE...THE INITIAL INTENSITY IS
INCREASED TO 65 KT.  

THE INITIAL MOTION IS NOW 345/12.  NADINE IS BETWEEN A DEEP-LAYER
RIDGE TO THE EAST AND A MID/UPPER-LEVEL LOW TO THE WEST.  THE
GLOBAL MODELS FORECAST THE CYCLONE TO MERGE WITH THE LOW BETWEEN
24-72 HR...WITH THE SYSTEM THEN CAUGHT IN AN AREA OF LIGHT STEERING
CURRENTS.  THE DYNAMICAL MODELS ARE IN GOOD AGREEMENT THAT NADINE
WILL SLOW DOWN AND MAKE A CYCLONIC LOOP DURING THE NEXT 72-96 HR. 
THE CANADIAN MODEL FORECASTS THE LARGEST LOOP...WITH THE CENTER OF
NADINE MOVING SOUTH OF 30N BEFORE TURNING EASTWARD.  THE NEW
FORECAST TRACK FOLLOWS THE LOOP SCENARIO...BUT TO KEEP CONTINUITY
WITH THE PREVIOUS FORECAST IT SHOWS LESS OF A SOUTHWARD MOTION THAN
INDICATED BY THE GUIDANCE.  AFTER 96 HR...THE GLOBAL MODELS
FORECAST A LARGE BAROCLINIC CYCLONE TO DEVELOP OVER THE
NORTHEASTERN ATLANTIC WITH THE ASSOCIATED WESTERLY WINDS EXTENDING
SOUTHWARD TO AT LEAST 30N.  THIS SYSTEM SHOULD STEER NADINE TO THE
EAST OR NORTHEAST NEAR THE END OF THE FORECAST PERIOD.

WATER VAPOR IMAGERY SHOWS A SHORTWAVE TROUGH THAT IS ROTATING AROUND
THE MID/UPPER-LEVEL LOW IS NOW APPROACHING NADINE FROM THE SOUTH.
IT IS POSSIBLE THIS SYSTEM WILL PROVIDE SOME UPPER-LEVEL DIVERGENCE
TO MAINTAIN THE CURRENT INTENSITY DESPITE THE SHEAR...SO THE NEW
INTENSITY FORECAST KEEPS NADINE A HURRICANE THROUGH 24 HR.  NADINE
COULD ENCOUNTER DECREASING SHEAR AS IT MERGES WITH THE LOW. 
HOWEVER...THE GUIDANCE IS IN POOR AGREEMENT ON THE DETAILS...WITH
THE GFS SHOWING CYCLONIC UPPER-LEVEL FLOW AROUND THE STORM AT 36 HR
AND THE ECMWF SHOWING ANTICYCLONIC FLOW.  THE INTENSITY FORECAST
SHOWS SOME WEAKENING DURING THE MERGER BASED ON THE PREMISE THAT IT
WILL AT LEAST SOMEWHAT DISRUPT THE STRUCTURE OF NADINE.  LATE IN
THE FORECAST PERIOD...INTERACTION BETWEEN NADINE AND THE BAROCLINIC
CYCLONE SHOULD LEAD TO EXTRATROPICAL TRANSITION.  THE FORECAST NOW
CALLS FOR THIS AT 120 HR...ALTHOUGH IT COULD BE DELAYED IF NADINE
IS SOUTH OF THE CURRENT FORECAST POSITION.
 
FORECAST POSITIONS AND MAX WINDS
 
INIT  29/1500Z 33.3N  36.2W   65 KT  75 MPH
 12H  30/0000Z 34.8N  36.7W   65 KT  75 MPH
 24H  30/1200Z 36.4N  37.5W   65 KT  75 MPH
 36H  01/0000Z 36.7N  38.1W   60 KT  70 MPH
 48H  01/1200Z 36.3N  38.1W   55 KT  65 MPH
 72H  02/1200Z 35.5N  38.0W   55 KT  65 MPH
 96H  03/1200Z 35.5N  36.5W   50 KT  60 MPH
120H  04/1200Z 38.0N  33.0W   45 KT  50 MPH...POST-TROP/EXTRATROP
 
$$
FORECASTER BEVEN
 
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