Subtropical Storm GABRIELLE

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SUBTROPICAL STORM GABRIELLE DISCUSSION NUMBER   1
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL   AL072007
1100 PM EDT FRI SEP 07 2007
 
THE AIR FORCE RESERVE HURRICANE HUNTER INVESTIGATING THE LOW
PRESSURE AREA OFF THE SOUTHEASTERN U. S. COAST COULD NOT FIND A
WELL-DEFINED CIRCULATION...REPORTING INSTEAD A VERY ELONGATED
CENTER.  SUBSEQUENT SATELLITE IMAGERY SUGGESTS THE CIRCULATION IS
SLIGHTLY BETTER DEFINED...BUT IS STILL BROAD AND ELONGATED.  THE
AIRCRAFT FOUND 48 KT FLIGHT-LEVEL WINDS ABOUT 85 N MI NORTHEAST OF
THE CENTER AND A CENTRAL PRESSURE OF ABOUT 1011 MB.  BASED ON THE
LARGE RADIUS OF MAXIMUM WINDS...THE CONVECTIVE STRUCTURE...AND THE
PROXIMITY OF AN UPPER-LEVEL LOW TO THE WEST-SOUTHWEST...THE SYSTEM
IS DESIGNATED A SUBTROPICAL STORM WITH WINDS OF 40 KT.
 
GABRIELL IS MOVING 300/8 BETWEEN A DEEP LAYER RIDGE OVER THE
NORTHWESTERN ATLANTIC AND AN UPPER-LEVEL LOW NEAR THE NORTHERN
BAHAMAS.  THE DYNAMICAL MODELS FORECAST THE CYCLONE TO RECURVE
AROUND THE WESTERN END OF THE EASTWARD-MOVING RIDGE DURING THE
NEXT 48-72 HR.  THE MODELS DISAGREE...HOWEVER...ON EXACTLY WHERE AND
WHEN THAT TURN WILL OCCUR.  THE GFDL IS THE LEFTMOST SOLUTION WITH
A FORECAST TRACK INTO EASTERN SOUTH CAROLINA IN ABOUT 36 HR...
FOLLOWED BY A NORTHEASTWARD MOTION ACROSS EASTERN NORTH CAROLINA
INTO THE ATLANTIC.  THE UKMET...NOGAPS...AND GFS CALL FOR LANDFALL
IN EASTERN NORTH CAROLINA IN 36-48 HR...FOLLOWED BY RECURVATURE
INTO THE ATLANTIC.  THE GFDL TRACK MAY BE RESULTING FROM HAVING TOO
DEEP OF A VORTEX INITIALLY...WHICH RESULTS IN TOO MUCH STEERING
INFLUENCE FROM THE UPPER-LEVEL LOW.  THUS...THE FORECAST TRACK
FOLLOWS THE MORE EASTWARD SCENARIO OF THE OTHER MODELS.
 
THERE ARE CURRENTLY MANY NEGATIVE FACTORS INVOLVED IN THE FUTURE
DEVELOPMENT OF GABRIELLE.  THE STORM HAS COOLER AIR TO THE NORTH
AT LOW LEVELS...VERY DRY AIR TO THE SOUTH AND WEST AT THE UPPER
LEVELS...IS EXPERIENCING SOUTHERLY VERTICAL WIND SHEAR...AND IS
PASSING OVER WATERS THAT HAVE COOLED A FEW DEGREES OVER THE PAST
COUPLE OF DAYS.  ON THE POSITIVE SIDE...THE SHEAR MAY DECREASE AS
GABRIELLE APPROACHES THE COAST...AND THIS COULD OCCUR OVER THE DEEP
WARM WATER OF THE GULF STREAM.  THE SHIPS MODEL CALLS FOR A PEAK
INTENSITY OF 63 KT...THE GFDL 68 KT...AND THE HWRF 37 KT.  GIVEN
ALL THE NEGATIVES...THE INTENSITY FORECAST WILL STAY ON THE LOW
SIDE OF THE GUIDANCE...CALLING FOR A PEAK INTENSITY OF 50 KT NEAR
LANDFALL.  AFTER RECURVATURE...GABRIELLE SHOULD GRADUALLY MERGE
WITH A FRONTAL ZONE AND BECOME EXTRATROPICAL.
 
IT SHOULD BE NOTED THAT THERE IS A POSSIBILITY OF CENTER REFORMATION
DUE TO THE ELONGATED NATURE OF THE SYSTEM.  WHILE SUCH REFORMATION
WOULD NOT CHANGE THE OVERALL STEERING PATTERN...IT COULD HAVE AN
AFFECT ON IF AND WHERE THE CENTER MAKES LANDFALL.
 
 
FORECAST POSITIONS AND MAX WINDS
 
INITIAL      08/0300Z 30.4N  72.2W    40 KT...SUBTROPICAL
 12HR VT     08/1200Z 31.1N  73.7W    40 KT...SUBTROPICAL
 24HR VT     09/0000Z 32.3N  75.5W    40 KT...SUBTROPICAL
 36HR VT     09/1200Z 33.5N  76.8W    45 KT...TROPICAL
 48HR VT     10/0000Z 35.0N  76.6W    50 KT...INLAND
 72HR VT     11/0000Z 37.5N  73.5W    40 KT...OVER WATER
 96HR VT     12/0000Z 40.5N  67.5W    45 KT...EXTRATROPICAL
120HR VT     13/0000Z 43.0N  58.0W    45 KT...EXTRATROPICAL
 
$$
FORECASTER BEVEN/ROBERTS
 
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