Tropical Storm FLORENCE

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TROPICAL STORM FLORENCE DISCUSSION NUMBER  23
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL   AL062006
500 AM EDT SAT SEP 09 2006
 
AN AIR FORCE RESERVE HURRICANE HUNTER AIRCRAFT REACHED THE CENTER OF
FLORENCE ABOUT 04Z...WITH A SECOND FIX ABOUT 0630Z.  THE AIRCRAFT
MEASURED MINIMUM PRESSURES OF 998 AND 993 MB ON THE TWO FIXES...
WITH MAXIMUM 850 MB FLIGHT-LEVEL WINDS OF 61 KT ABOUT 50 N MI
NORTHEAST OF THE CENTER.  SATELLITE INTENSITY ESTIMATES ARE 65 KT
FROM SAB AND AFWA...AND 55 KT FROM TAFB.  THE INITIAL INTENSITY
REMAINS 55 KT FOR THIS ADVISORY.  IT SHOULD BE NOTED THAT THE
AIRCRAFT AND RECENT AMSR-E DATA SHOW THAT WHILE THE CONVECTION IS
STRONG...IT IS CURRENTLY CONFINED TO THE NORTHERN QUADRANT.

THE AIRCRAFT FOUND THE CENTER SOUTH OF THE PREVIOUS FORECAST
TRACK...AND A REVIEW OF EARLIER SATELLITE DATA SUGGESTS THAT
FLORENCE HAS BEEN MOVING WEST-NORTHWESTWARD FOR THE PAST 12 HR OR
SO.  THE INITIAL MOTION IS 300/12.  OTHER THAN THIS...THERE IS NO
CHANGE IN THE FORECAST PHILOSOPHY.  WATER VAPOR IMAGERY SHOWS THAT
FLORENCE IS APPROACHING THE WESTERN END OF A DEEP-LAYER RIDGE...
WITH AN UPPER-LEVEL LOW SOUTHWEST OF THE STORM NEAR 21N71W AND A
MID/UPPER-LEVEL SHORTWAVE TROUGH APPROACHING THE EAST COAST OF THE
UNITED STATES.  THIS COMBINATION SHOULD TURN FLORENCE NORTHWARD
DURING THE NEXT 12-36 HR...WITH THE STORM RECURVING NORTHEASTWARD
IN DEEP-LAYER SOUTHWESTERLY FLOW THEREAFTER.  ALL MODEL GUIDANCE
AGREES ON THE RECURVATURE...WITH LBAR CALLING FOR THE FARTHEST WEST
RECURVATURE AT 68W.  THERE REMAINS SOME SPREAD IN THE MODEL
GUIDANCE AFTER RECURVATURE.  THE NOGAPS...GFDN...GFDL...AND ECMWF
BRING THE CENTER OVER SOUTHEASTERN NEWFOUNDLAND...WHILE THE
REMAINDER OF THE GUIDANCE KEEPS IT SOUTHEAST OF THE ISLAND.  THE
NEW FORECAST TRACK IS MOVED WESTWARD FOR THE FIRST 48 HR DUE TO THE
CURRENT POSITION AND MOTION...AND NOW CALLS FOR FLORENCE TO PASS
VERY NEAR BERMUDA IN 48-72 HR.  THE LATTER PART OF THE FORECAST IS
SIMILAR TO THE PREVIOUS PACKAGE.  OVERALL...THE NEW FORECAST TRACK
IS JUST TO THE LEFT OF THE MODEL CONSENSUS.

ANALYSES FROM CIMSS AT THE UNIVERSITY OF WISCONSIN INDICATE THAT THE
VERTICAL SHEAR HAS DECREASED TO ABOUT 10 KT.  FLORENCE HAS ABOUT A
48-60 HR WINDOW IN WHICH TO INTENSIFY BEFORE ENCOUNTERING STRONG
SHEAR IN THE WESTERLIES.  THE SHIPS AND FSU SUPERENSEMBLE BOTH
FORECAST A PEAK INTENSITY OF 100-105 KT IN ABOUT 60 HR...WHILE THE
GFDL CALLS FOR A PEAK INTENSITY OF 87 KT.  THE INTENSITY FORECAST
IS AN UPDATE OF THE PREVIOUS PACKAGE...CALLING FOR A PEAK INTENSITY
OF 90 KT IN ABOUT 48 HR.  AFTER FLORENCE ENTERS THE WESTERLIES...
INCREASING VERTICAL SHEAR AND COLD AIR INTRUSION SHOULD CAUSE
WEAKENING AND EXTRATROPICAL TRANSITION BY 120 HR.  HOWEVER...
FLORENCE SHOULD REMAIN A LARGE AND VIGOROUS CYCLONE THROUGH THE
TRANSITION PROCESS.
 
FORECAST POSITIONS AND MAX WINDS
 
INITIAL      09/0900Z 24.1N  62.8W    55 KT
 12HR VT     09/1800Z 25.1N  64.3W    65 KT
 24HR VT     10/0600Z 26.7N  65.4W    75 KT
 36HR VT     10/1800Z 28.6N  65.9W    85 KT
 48HR VT     11/0600Z 30.6N  65.8W    90 KT
 72HR VT     12/0600Z 36.0N  63.0W    85 KT
 96HR VT     13/0600Z 43.0N  56.0W    70 KT...BECOMING EXTRATROPICAL
120HR VT     14/0600Z 49.0N  46.0W    60 KT...EXTRATROPICAL
 
$$
FORECASTER BEVEN
 
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