000
WTNT44 KNHC 070240
TCDAT4
TROPICAL STORM COLIN DISCUSSION NUMBER  13
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL   AL042010
1100 PM AST FRI AUG 06 2010
 

COLIN IS A SHEARED CYCLONE WITH INCREASING CONVECTION NEAR AND TO
THE EAST OF THE CENTER AT THIS TIME. THIS COULD GIVE AN IMPRESSION
OF A STRONGER CYCLONE BUT FLUCTUATIONS IN CONVECTION ARE TYPICAL IN
SHEARED SYSTEMS.  THE STRONG UPPER-LEVEL WINDS CURRENTLY OVER THE
CYCLONE WILL PROBABLY SEPARATE THE CENTER FROM THE THUNDERSTORM
ACTIVITY AGAIN SOON. THEREFORE...THE INITIAL INTENSITY IS KEPT AT
40 KNOTS. ANOTHER RECONNAISSANCE PLANE WILL CHECK COLIN IN SEVERAL
HOURS. COLIN HAS A SMALL WINDOW OF OPPORTUNITY TO GATHER SOME
STRENGTH WITHIN THE NEXT DAY OR SO...IF THE SHEAR RELAXES A BIT AS
DIAGNOSED BY THE SHIPS MODEL. IN FACT...IF THE CURRENT INCREASE IN
CONVECTION CONTINUES OR PERSIST IT COULD MEAN THAT THE SHEAR IS
ALREADY RELAXING AND SLIGHT INTENSIFICATION IS ABOUT TO BEGIN. THE
OFFICIAL FORECAST ASSUMES THAT THE SHEAR WILL RELAX A BIT AND CALLS
FOR A SMALL INCREASE IN INTENSITY. BY 96 HOURS...COLIN SHOULD BE
EXTRATROPICAL AND THEN BECOME ABSORBED BY A LARGER CYCLONE. THE
INTENSIFICATION SHOWN IN BOTH THE GFDL AND HWRF MODELS OCCURS LATE
IN THE FORECAST PERIOD. THIS DOES NOT SEEM TO BE REALISTIC BECAUSE
BY THEN...THE CYCLONE IS EXPECTED TO BE REACHING COOLER WATERS AND
BECOMING EXTRATROPICAL.  

THE CENTER IS CLEARLY OBSERVED ON THE WESTERN EDGE OF THE CONVECTION
AND ONE CAN OBTAIN A GOOD ESTIMATE OF THE INITIAL MOTION...WHICH IS
TOWARD THE NORTH OR 010 DEGREES AT 8 KNOTS. COLIN IS ALREADY ON THE
WESTERN EDGE OF THE SUBTROPICAL RIDGE AND IS NEARING THE
MID-LATITUDE WESTERLIES. THEREFORE...THE CYCLONE SHOULD GRADUALLY
TURN MORE TO THE NORTH-NORTHEAST WITH SOME INCREASE IN FORWARD
SPEED. THERE IS GOOD CONFIDENCE IN THE FORECAST BECAUSE THE TRACK
GUIDANCE IS PACKED AND THE OFFICIAL FORECAST IS IN THE MIDDLE OF
THE ENVELOPE. THE ONLY DIFFERENCE IS IN THE FORWARD SPEED SHOWN BY
VARIOUS MODELS...BUT THIS MOSTLY OCCUR AT THE LONG RANGE AS THE
SYSTEM BEGINS THE TRANSITION TO AN EXTRATROPICAL LOW.       

 
FORECAST POSITIONS AND MAX WINDS
 
INITIAL      07/0300Z 29.1N  66.5W    40 KT
 12HR VT     07/1200Z 30.3N  66.1W    40 KT
 24HR VT     08/0000Z 32.0N  65.2W    45 KT
 36HR VT     08/1200Z 33.7N  64.4W    55 KT
 48HR VT     09/0000Z 36.5N  63.0W    55 KT
 72HR VT     10/0000Z 42.0N  57.5W    55 KT
 96HR VT     11/0000Z 49.5N  46.5W    45 KT...POST-TROP/EXTRATROP
120HR VT     12/0000Z...ABSORBED BY A LARGER EXTRATROPICAL CYCLONE 
 
$$
FORECASTER AVILA