Subtropical Storm GABRIELLE

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SUBTROPICAL STORM GABRIELLE DISCUSSION NUMBER   3
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL   AL072007
1100 AM EDT SAT SEP 08 2007
 
MORNING VISIBLE IMAGERY REVEALS A FULLY EXPOSED BUT WELL-DEFINED
LOW-LEVEL CENTER OF CIRCULATION.  DEEP CONVECTION...BUT WITH
RELATIVELY WARM CLOUD TOPS NEAR -65C...REMAINS CONFINED NORTH OF
THE CENTER AND IS MOST ABUNDANT IN THE NORTHWESTERN QUADRANT WITH A
DISTANT AND THINNING BAND TO THE NORTHEAST.  A QUIKSCAT OVERPASS AT
ABOUT 1115Z CAPTURED ONLY THE WESTERN HALF OF THE CIRCULATION...BUT
DID INDICATE SOME BELIEVABLE 40 KT RETRIEVALS BETWEEN ABOUT 60 AND
90 NMI FROM THE CENTER...SO THE ADVISORY INTENSITY REMAINS 40 KT. 
EVEN THOUGH THE CONVECTION IS BECOMING MORE PERSISTENT NEAR THE
CENTER...THE STATUS REMAINS SUBTROPICAL GIVEN THAT THE RADIUS OF
MAXIMUM WINDS REMAINS LARGE.  A SHIP WITH CALL SIGN DDSB2 RECENTLY
REPORTED WINDS OF 33 KT AND A PRESSURE OF 1011 MB ABOUT 20 NMI
NORTHWEST OF THE CENTER...SO THE CENTRAL PRESSURE IS LOWERED
SLIGHTLY TO 1009 MB.  AN AIR FORCE RECONNAISSANCE AIRCRAFT IS
SCHEDULED TO INVESTIGATE GABRIELLE THIS AFTERNOON TO HELP US GET A
MORE THOROUGH LOOK AT THE WIND FIELD.

THE CENTER OF GABRIELLE IS MOVING JUST SLIGHTLY TO THE RIGHT OF THE
PREVIOUS OFFICIAL TRACK...AND THE INITIAL MOTION ESTIMATE IS
305/9...WHICH IS ALSO A TAD SLOWER THAN BEFORE.  THE STORM
CONTINUES TO BE STEERED BY THE RIDGE TO ITS NORTHEAST...AND THE
FORECAST SCENARIO REMAINS THAT GABRIELLE WILL ROTATE AROUND THE
WESTERN PERIPHERY OF THIS RIDGE AND INTO THE MIDLATITUDE WESTERLIES
DURING THE NEXT 2-3 DAYS.  THE LATEST MODEL GUIDANCE HAS GENERALLY
SHIFTED SLIGHTLY TO THE RIGHT...AND ESPECIALLY GIVEN THE INITIAL
MOTION...SO HAS THE OFFICIAL FORECAST.  THE NEW TRACK IS CLOSE TO A
BLEND OF THE HWRF...GFDL...AND GFS AND SHOWS LANDFALL ALONG THE
OUTER BANKS IN ABOUT 36 HOURS.  THE SPREAD IN THE MODELS IS
SUFFICIENTLY LARGE...HOWEVER...THAT A LANDFALL FARTHER EAST OR NO
LANDFALL OF THE CENTER AT ALL ARE BOTH POSSIBILITIES.  AFTER
PASSING NEAR OR OVER EASTERN NORTH CAROLINA...GABRIELLE SHOULD MOVE
FAIRLY QUICKLY BACK OUT TO SEA AND BECOME EXTRATROPICAL BY DAY 4.

A SHORT WINDOW OF OPPORTUNITY EXISTS FOR GABRIELLE TO STRENGTHEN
BEFORE REACHING NORTH CAROLINA...SINCE THE CURRENT SOUTHEASTERLY
WIND SHEAR IS FORECAST BY THE GLOBAL MODELS TO TEMPORARILY LESSEN
TONIGHT BEFORE INCREASING AGAIN TOMORROW AS THE UPPER-LEVEL LOW TO
THE SOUTHWEST MOVES FARTHER AWAY.  GIVEN THE LIMITED EXTENT OF THE
CONVECTION CURRENTLY...THAT CHANGE IN ENVIRONMENT IS PROBABLY NOT
ENOUGH TO WARRANT A FORECAST OF SIGNIFICANT STRENGTHENING.  THE NEW
OFFICIAL FORECAST IS VERY SIMILAR TO THE PREVIOUS ADVISORY IN
BRINGING GABRIELLE TO 55 KT BY 36 HOURS...IN LINE WITH MOST OF THE
OBJECTIVE GUIDANCE.  GRADUAL WEAKENING IS FORECAST BEYOND 72 HOURS
AS EXTRATROPICAL TRANSITION OCCURS.
 
 
 
FORECAST POSITIONS AND MAX WINDS
 
INITIAL      08/1500Z 31.5N  74.2W    40 KT
 12HR VT     09/0000Z 32.4N  75.3W    45 KT...TROPICAL
 24HR VT     09/1200Z 33.8N  76.0W    50 KT
 36HR VT     10/0000Z 35.2N  75.6W    55 KT...NEAR NC COAST
 48HR VT     10/1200Z 36.4N  74.0W    55 KT
 72HR VT     11/1200Z 39.0N  68.0W    55 KT
 96HR VT     12/1200Z 44.0N  58.0W    50 KT...EXTRATROPICAL
120HR VT     13/1200Z 46.0N  46.0W    45 KT...EXTRATROPICAL
 
$$
FORECASTER KNABB
 
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