Tropical Storm BONNIE

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TROPICAL STORM BONNIE DISCUSSION NUMBER   7
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL
5 PM EDT MON AUG 09 2004
 
AN AIR FORCE RESERVE RECONNAISSANCE AIRCRAFT INVESTIGATING THE
REMNANTS OF FORMER TROPICAL DEPRESSION TWO FOUND A SMALL BUT VERY
TIGHT SURFACE CIRCULATION AND 56 KT 1500 FT FLIGHT-LEVEL WINDS.
NORMALLY THIS WOULD EQUATE TO 48 SURFACE WINDS...BUT THE CONVECTION
OVER THE CENTER IS SMALL AND NOT PARTICULARLY WELL ORGANIZED. THE
RAPID SPIN UP IN THE LOW-LEVEL WIND FIELD COULD EASILY SPINDOWN IF
THE INNER-CORE CONVECTION WEAKENS OR DISSIPATES. SO THE INITIAL
INTENSITY IS A BLEND OF THE RECON WINDS AND A DVORAK SATELLITE
INTENSITY ESTIMATE OF T2.5...OR 35 KT...FROM TAFB.
 
THE INITIAL MOTION ESTIMATE IS 310/10. THERE IS LIMITED MODEL
GUIDANCE AVAILABLE FOR THIS FORECAST PACKAGE SINCE NONE OF THE
GLOBAL MODELS INITIALIZED THE BONNIE CIRCULATION VERY WELL AT 12Z.
HOWEVER...ALL OF THE GLOBAL AND REGIONAL MODELS AGREE ON TAKING A
WEAK MID-LEVEL TROUGH FROM OVER THE SOUTHERN PLAINS SOUTHEASTWARD
TO THE NORTH-CENTRAL GULF OF MEXICO AND WEAKENING THE SUBTROPICAL
RIDGE TO THE NORTH OF BONNIE. THE RESULT SHOULD BE A GRADUAL TURN
TOWARD THE NORTH WITH A DECREASE IN FORWARD SPEED AS THE STEERING
CURRENTS WEAKEN. BY 48 HOURS...BONNIE IS EXPECTED TO TURN
NORTHEASTWARD AND GRADUALLY ACCELERATE AHEAD OF A SECOND AND
STRONGER MID-LEVEL TROUGH THAT IS FORECAST TO PUSH SOUTHEASTWARD
INTO THE WESTERN GULF OF MEXICO IN 48 TO 72 HOURS. THE OFFICIAL
FORECAST TRACK IS A BLEND OF THE GFDL...DEEP AND MEDIUM BAM...AND
THE GFS 10-MEMBER ENSEMBLE MODEL FORECASTS.
 
THE INTENSITY FORECAST IS SOMEWHAT PROBLEMATIC. BONNIE HAS A SMALL
AND TIGHT CIRCULATION...AND WILL BE MOVING INTO A LOWER VERTICAL
SHEAR REGION OVER THE CENTRAL GULF OF MEXICO...WHICH WOULD NORMALLY
FAVOR SIGNIFICANT INTENSIFICATION TO OCCUR. THE SHIPS MODEL BRINGS
BONNIE TO 83 KT IN 72 HOURS...WHILE THE GFDL TAKES THE CYCLONE UP
TO 74 KT AT THE SAME TIME PERIOD. THE ARGUMENT AGAINST FORECASTING
ANY ROBUST INTENSIFICATION FROM OCCURRING...AT LEAST IN THE SHORT
TERM...IS THE ABUNDANCE OF VERY DRY AIR SURROUNDING THE CYCLONE...
AS SEEN IN WATER VAPOR IMAGERY...THAT BONNIE WILL HAVE TO NAVIGATE
THROUGH FOR THE NEXT 24 TO 48 HOURS. 
 
FORECASTER STEWART
 
FORECAST POSITIONS AND MAX WINDS
 
INITIAL      09/2100Z 23.2N  88.7W    40 KT
 12HR VT     10/0600Z 24.3N  90.0W    45 KT
 24HR VT     10/1800Z 25.3N  90.3W    45 KT
 36HR VT     11/0600Z 26.5N  90.2W    50 KT
 48HR VT     11/1800Z 27.4N  89.5W    50 KT
 72HR VT     12/1800Z 30.0N  86.5W    50 KT
 96HR VT     13/1800Z 34.0N  80.5W    25 KT...INLAND
120HR VT     14/1800Z...DISSIPATED
 
 
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