[Tropical] Tropical Cyclone Discussion

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WTNT41 KNHC 270233
TCDAT1
TROPICAL STORM FRANKLIN DISCUSSION NUMBER  23
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL
11 PM EDT TUE JUL 26 2005

A CONVECTIVE CLUSTER WITH TOPS OF -70C TO -75C PERSISTS NEAR AND
SOUTH OF THE LOW-LEVEL CENTER OF FRANKLIN.  SHEAR ANALYSES FROM
CIMSS AT THE UNIVERSITY OF WISCONSIN INDICATE THAT THE VERTICAL
SHEAR HAS DECREASED DURING THE PAST 12 HR...AND THIS IS LIKELY
RESPONSIBLE FOR THE CONVECTIVE INCREASE.  SATELLITE INTENSITY
ESTIMATES ARE 35 KT FROM TAFB AND SAB...AND 30 KT FROM AFWA...WHILE
A RECENT QUIKSCAT OVERPASS SHOWS RAIN-CONTAMINATED 40 KT VECTORS
SOUTHEAST OF THE CENTER.  THE INITIAL INTENSITY REMAINS 35 KT AS A
COMPROMISE BETWEEN THE VARIOUS ESTIMATES.

CIRRUS OUTFLOW FROM THE CONVECTION HAS COVERED THE CENTER...SO THE
INITIAL MOTION IS QUITE UNCERTAIN.  THE 24 HR MOTION IS 005/4.
HOWEVER...THIS PACKAGE WILL USE A 315/2 DRIFT THAT HAS OCCURRED
OVER THE PAST SEVERAL HOURS.  WATER VAPOR IMAGERY SHOWS A MID/
UPPER-LEVEL RIDGE PASSING NORTH OF FRANKLIN.  AS THIS FEATURE MOVES
EASTWARD...PRESSURES SHOULD RISE EAST OF BERMUDA AS THEY FALL OVER
THE EASTERN U. S. EAST OF THE NEXT TROUGH AND ASSOCIATED COLD
FRONT...CURRENTLY OVER THE NORTHERN PLAINS AND GREAT LAKES.
LARGE-SCALE MODELS AGREE THAT THESE CHANGES SHOULD COME ABOUT IN
12-24 HR...AND THAT FRANKLIN SHOULD MOVE NORTHWARD IN RESPONSE.
THE CYCLONE THEN SHOULD GRADUALLY TURN NORTHEASTWARD AFTER 24-36 HR
AND ACCELERATE INTO THE WESTERLIES THROUGH THE REST OF ITS LIFE.
THE OFFICIAL FORECAST TRACK AGREES WITH THIS SCENARIO.  THE NEW
TRACK IS NEAR THE LEFT EDGE OF THE MAIN ENVELOPE OF GUDIANCE...AND
SLOWER THAN THE GUIDANCE BASED ON THE RECENT TRACK RECORD OF THE
GUIDANCE BEING TOO FAST.  IT WOULD NOT BE SURPRISING TO SEE SOME
WEST OF NORTH MOTION IN THE FIRST 12 HR OF THE FORECAST PERIOD.

THE CURRENT DECREASE IN SHEAR IS OCCURRING AS AN UPPER-LEVEL
CYCLONIC SHEAR AXIS FORMS NEAR FRANKLIN...A PATTERN THAT OVERALL IS
NOT THAT FAVORABLE FOR STRENGTHENING.  LARGE-SCALE MODELS FORECAST
THIS FEATURE TO WEAKEN AND MOVE SOUTH OF FRANKLIN IN ABOUT 12-24
HR... WHICH WOULD OPEN ABOUT A 24 HR WINDOW FOR THE STORM TO
STRENGTHEN BEFORE IT MOVES NORTH OF THE GULF STREAM.  THE INTENSITY
FORECAST CALLS FOR MODEST STRENGTHENING TO 40 KT...WHICH IS ABOUT
THE MOST THE INTENSITY GUIDANCE IS CURRENTLY FORECASTING.

FORECASTER BEVEN


FORECAST POSITIONS AND MAX WINDS

INITIAL      27/0300Z 32.4N  68.6W    35 KT
 12HR VT     27/1200Z 33.1N  68.6W    35 KT
 24HR VT     28/0000Z 34.4N  68.4W    40 KT
 36HR VT     28/1200Z 36.0N  67.8W    40 KT
 48HR VT     29/0000Z 38.0N  66.5W    40 KT...BECOMING EXTRATROPICAL
 72HR VT     30/0000Z 41.5N  61.5W    30 KT...EXTRATROPICAL
 96HR VT     31/0000Z...DISSIPATED


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