Tropical Storm KIRK

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TROPICAL STORM KIRK DISCUSSION NUMBER   5
NWS NATIONAL HURRICANE CENTER MIAMI FL       AL112012
500 PM AST WED AUG 29 2012

DEEP CONVECTION HAS BLOSSOMED OVER THE CENTER OF KIRK THIS
AFTERNOON...BUT CLOUD TOP TEMPERATURES HAVE BEGUN TO WARM AGAIN
OVER THE PAST HOUR OR SO. THE INITIAL INTENSITY IS SET TO 45 KT
BASED ON THE LATEST DVORAK ESTIMATES FROM TAFB AND SAB. IN THE
SHORT TERM...MODERATE SHEAR VALUES AND SOME DRY AIR IN THE
ENVIRONMENT WOULD SEEM TO SUPPORT ONLY GRADUAL STRENGTHENING IN THE
NEXT DAY OR SO. BEYOND 36 HOURS...THE SHEAR IS EXPECTED TO DECREASE
AS KIRK MOVES AROUND THE WESTERN SIDE OF THE SUBTROPICAL RIDGE...
AND MOST OF THE GUIDANCE SHOWS KIRK BECOMING A HURRICANE BY 72
HOURS. WEAKENING IS EXPECTED BY DAY 4 AS THE SHEAR INCREASES
DRAMATICALLY AND KIRK MOVES OVER COOLER WATERS BEFORE THE CYCLONE
IS ABSORBED BY DAY 5. THROUGH THE PERIOD THE NHC FORECAST IS CLOSE
TO THE VARIOUS INTENSITY CONSENSUS AIDS. 

THE CENTER NOW APPEARS TO BE EMBEDDED UNDER THE DEEP CONVECTION AND
IS ABOUT A HALF A DEGREE TO THE RIGHT OF THE PREVIOUS FORECAST. THE
INITIAL MOTION ESTIMATE IS A RATHER UNCERTAIN 300/09. OVERALL THE
TRACK FORECAST REASONING REMAINS UNCHANGED...AS KIRK WILL MOVE
AROUND THE WESTERN SIDE OF THE SUBTROPICAL RIDGE IN THE NEXT 24
HOURS AND THEN BEGIN TO ACCELERATE NORTHWARD AND NORTHEASTWARD AS
THE CYCLONE RECURVES AHEAD OF AN AMPLIFYING MID-LATITUDE TROUGH.
MOST OF THE GUIDANCE HAS SHIFTED TOWARD A SHARPER RECURVATURE THIS
CYCLE WITH A FASTER FORWARD SPEED LATE IN THE PERIOD. FOR
EXAMPLE...THE ECMWF...WHICH WAS ON THE LEFT SIDE OF THE GUIDANCE
ENVELOPE EARLIER NOW LIES CLOSER TO THE MIDDLE OF THE ENVELOPE BUT
IS EAST OF THE CONSENSUS. OVERALL THE MODEL CONSENSUS HAS SHIFTED
RIGHTWARD THIS CYCLE...AND THIS...IN COMBINATION WITH THE
ADJUSTMENT IN THE INITIAL POSITION AND MOTION...RESULTS IN A
RIGHTWARD SHIFT OF ABOUT A DEGREE IN THE NHC TRACK IN THE FIRST 36
HOURS. BEYOND THAT TIME...THE NHC FORECAST IS BLENDED BACK TOWARD
THE OLD TRACK...BUT IS FASTER. THROUGHOUT THE PERIOD THE NHC TRACK
IS NEAR THE TVCA CONSENSUS. 
 
FORECAST POSITIONS AND MAX WINDS
 
INIT  29/2100Z 25.3N  47.6W   45 KT  50 MPH
 12H  30/0600Z 26.1N  48.9W   50 KT  60 MPH
 24H  30/1800Z 27.7N  50.4W   50 KT  60 MPH
 36H  31/0600Z 29.6N  51.3W   55 KT  65 MPH
 48H  31/1800Z 31.9N  51.1W   60 KT  70 MPH
 72H  01/1800Z 38.0N  46.0W   70 KT  80 MPH
 96H  02/1800Z 45.5N  37.0W   60 KT  70 MPH
120H  03/1800Z...ABSORBED
 
$$
FORECASTER BRENNAN
 
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