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Tropical Storm ROSA (Text)

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TROPICAL STORM ROSA DISCUSSION NUMBER   6
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL   EP192006
700 AM PST THU NOV 09 2006
 
DESPITE EXPERIENCING MODERATE TO STRONG SOUTHWESTERLY VERTICAL
SHEAR...CONVECTION HAS FORMED OVER THE CENTER AND PERSISTED DURING
THE LAST FEW HOURS.  SUBJECTIVE DVORAK INTENSITY ESTIMATES ARE 30
KT AND 35 KT FROM SAB AND TAFB RESPECTIVELY.  THE EXPERIMENTAL
OBJECTIVE DVORAK ESTIMATE FROM UW-CIMSS HAS BEEN RUNNING A BIT
HIGHER.  BASED ON A BLEND OF THE DVORAK INTENSITY ESTIMATES AND THE
RECENT IMPROVEMENT IN ORGANIZATION...THE CYCLONE IS UPGRADED TO A
TROPICAL STORM WITH 35 KT WINDS.  EVEN THOUGH ROSA IS SHOWING SIGNS
OF STRENGTHENING THIS MORNING...GLOBAL MODELS INDICATE VERTICAL
SHEAR WILL STEADILY INCREASE OVER THE NEXT COUPLE OF DAYS AS AN
UPPER-LEVEL TROUGH TO THE NORTH OF THE CYCLONE DIGS SOUTHEASTWARD. 
ACCORDINGLY...THE OFFICIAL FORECAST CALLS FOR WEAKENING BEYOND 12
HOURS. BY 48 HOURS...ROSA IS EXPECTED TO BE A NON-CONVECTIVE LOW
WITH GRADUAL SPIN DOWN THEREAFTER. 
 
GIVEN THE RECENT BURST OF CONVECTION...ROSA HAS BEEN STEERED BY THE
DEEP-LAYERED FLOW DURING THE LAST FEW HOURS RESULTING IN AN ALMOST
DUE NORTH MOTION.  THE INITIAL MOTION ESTIMATE IS BASED ON A
LONGER-TERM AVERAGE YIELDING 340/6.  ROSA IS EXPECTED TO BECOME AN
INCREASINGLY SHALLOW CYCLONE IN 12-24 HOURS RESULTING IN A TURN
MORE TOWARD THE NORTHWEST AND A REDUCTION IN FORWARD SPEED. 
HOWEVER...IT SHOULD BE NOTED THAT SIGNIFICANT DIFFERENCES EXIST IN
THE SHALLOW AND DEEP-LAYER STEERING.  THIS INTRODUCES UNCERTAINTY
IN THE TRACK FORECAST AS IT IS DIFFICULT TO KNOW FOR SURE EXACTLY
HOW LONG DEEP CONVECTION WILL PERSIST OVER THE CENTER. SHOULD THE
CYCLONE BE ABLE TO HANG ON A LITTLE LONGER THAN ANTICIPATED...A
TRACK MORE TOWARD THE NORTH AND CLOSER TO THE COAST OF MEXICO IS
POSSIBLE.  HOWEVER...NONE OF THE GLOBAL MODELS INDICATE LANDFALL
ALONG SOUTHWESTERN MEXICO AT THIS TIME. 
 
FORECAST POSITIONS AND MAX WINDS
 
INITIAL      09/1500Z 15.7N 105.4W    35 KT
 12HR VT     10/0000Z 16.4N 105.7W    35 KT
 24HR VT     10/1200Z 16.8N 106.1W    30 KT
 36HR VT     11/0000Z 17.2N 106.5W    30 KT
 48HR VT     11/1200Z 17.6N 107.0W    25 KT...DISSIPATING
 72HR VT     12/1200Z 18.0N 108.0W    25 KT...REMNANT LOW
 96HR VT     13/1200Z 18.0N 108.5W    20 KT...REMNANT LOW
120HR VT     14/1200Z...DISSIPATED
 
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