000
WTNT42 KNHC 050236
TCDAT2
 
TROPICAL STORM GABRIELLE DISCUSSION NUMBER   2
NWS NATIONAL HURRICANE CENTER MIAMI FL       AL072013
1100 PM AST WED SEP 04 2013
 
THE SATELLITE PRESENTATION OF THE CYCLONE CONSISTS OF A SMALL AREA
OF VERY DEEP CONVECTION NEAR AND NORTHEAST OF THE SURFACE CENTER
WHILE THE CONVECTIVE BANDS HAVE LARGELY DISSIPATED OVER THE PAST
FEW HOURS. THE LARGE-SCALE OUTFLOW PATTERN OVER THE CYCLONE IS
EXCELLENT WITH AN ENHANCED POLEWARD OUTFLOW CHANNEL SEEN IN WATER
VAPOR IMAGERY. BASED ON THE LATEST SATELLITE CLASSIFICATIONS FROM
BOTH TAFB AND SAB...THE INITIAL INTENSITY IS SET TO 35 KT...AND THE
DEPRESSION IS NOW TROPICAL STORM GABRIELLE.
 
DROPSONDE DATA FROM THE NASA GLOBAL HAWK AIRCRAFT SUGGEST THAT THE
CIRCULATION OF GABRIELLE IS TILTED TO THE NORTHEAST WITH HEIGHT...
WITH A MID-LEVEL CIRCULATION SEEN IN DATA FROM THE SAN JUAN WSR-88D
RADAR. THIS TILTED STRUCTURE IS CONSISTENT WITH SOUTHERLY TO
SOUTHWESTERLY VERTICAL SHEAR OF 5 TO 10 KT SHOWN OVER THE CYCLONE
BY THE UW-CIMSS AND SHIPS MODEL ANALYSES. IN ADDITION...THE
DROPSONDE DATA SHOWED DRY AIR IN THE MID LEVELS OF THE ATMOSPHERE
AROUND GABRIELLE. GIVEN THE ENVIRONMENT...THE SOMEWHAT DISORGANIZED
STATE OF THE CIRCULATION...POSSIBLE LAND INTERACTION...AND THE
PRESENCE OF THE LARGE AREA OF DISTURBED WEATHER NORTHEAST OF
GABRIELLE...NOT MUCH STRENGTHENING IS EXPECTED IN THE SHORT TERM.
THE NHC FORECAST IS IN GOOD AGREEMENT WITH THE INTENSITY CONSENSUS
AIDS FOR THE FIRST 24 HOURS. IT IS ENTIRELY POSSIBLE THAT THE
LOW-LEVEL CIRCULATION WILL DISSIPATE IN THE NEXT 24 HOURS. ASSUMING
THAT GABRIELLE SURVIVES...ONLY LIMITED INTENSIFICATION IS SHOWN
LATER IN THE PERIOD AS THE SHEAR INCREASES DRAMATICALLY AHEAD OF AN
UPPER-LEVEL TROUGH. THE NHC FORECAST REMAINS BELOW MUCH OF THE
INTENSITY GUIDANCE LATE IN THE PERIOD...WHICH SEEMS TOO HIGH GIVEN
THE INCREASE IN SHEAR. THE NHC FORECAST IS ALSO SUPPORTED BY THE
GLOBAL MODELS...WHICH DO NOT SHOW MUCH INTENSIFICATION AFTER
GABRIELLE MOVES NORTH OF THE CARIBBEAN SEA.
 
THE LOW-LEVEL CENTER HAS BEEN DIFFICULT TO LOCATE...BUT THE GLOBAL
HAWK DROPSONDE DATA SUGGEST IT REMAINS SOUTHWEST OF THE MID-LEVEL
CENTER SEEN IN RADAR IMAGERY. GIVEN THE DIFFICULTY LOCATING THE
CENTER...THE INITIAL MOTION ESTIMATE IS AN UNCERTAIN 320/7. THE
SYNOPTIC-SCALE TRACK REASONING HAS NOT CHANGED...AS GABRIELLE IS
EXPECTED TO MOVE GENERALLY NORTHWESTWARD DURING THE NEXT DAY OR
SO...FOLLOWED A TURN TOWARD THE NORTH BY 72 HOURS AS THE CYCLONE
MOVES AROUND THE WESTERN PERIPHERY OF THE SUBTROPICAL RIDGE. LATE
IN THE PERIOD AN ACCELERATION TOWARD THE NORTHEAST IS EXPECTED AHEAD
OF AN UPPER-LEVEL TROUGH OVER THE WESTERN ATLANTIC. THE NHC TRACK
FORECAST IS LARGELY AN UPDATE OF THE PREVIOUS ONE THROUGH 72 HOURS
AND LIES A LITTLE TO THE RIGHT OF MOST OF THE MODEL GUIDANCE DURING
THIS PERIOD. AT DAYS 4 AND 5 THE NHC FORECAST IS A LITTLE TO THE
RIGHT OF THE PREVIOUS ONE AND IS CLOSE TO THE GFS ENSEMBLE MEAN AND
FSU SUPERENSEMBLE. 
 
REGARDLESS OF THE EXACT TRACK OF THE CENTER OF GABRIELLE DURING THE
NEXT 24 HOURS...THE MAIN THREAT WILL BE HEAVY RAINFALL OVER
PORTIONS OF PUERTO RICO AND THE DOMINICAN REPUBLIC.
  
 
FORECAST POSITIONS AND MAX WINDS
 
INIT  05/0300Z 17.0N  66.6W   35 KT  40 MPH
 12H  05/1200Z 17.8N  67.4W   40 KT  45 MPH
 24H  06/0000Z 19.0N  68.4W   45 KT  50 MPH
 36H  06/1200Z 20.1N  69.0W   45 KT  50 MPH
 48H  07/0000Z 21.2N  69.4W   45 KT  50 MPH
 72H  08/0000Z 23.3N  69.2W   50 KT  60 MPH
 96H  09/0000Z 25.5N  67.5W   50 KT  60 MPH
120H  10/0000Z 29.5N  63.9W   50 KT  60 MPH
 
$$
FORECASTER BRENNAN