Official Discussion issued by the National Hurricane Center

THIRTEEN (AL132011) DATA RELEASED: 9/1/2011 7:00:00 PM UTC

Copy of official data

TROPICAL DEPRESSION THIRTEEN SPECIAL DISCUSSION NUMBER   1
NWS NATIONAL HURRICANE CENTER MIAMI FL       AL132011
700 PM CDT THU SEP 01 2011

SATELLITE...SURFACE...AND NOAA RECONNAISSANCE AIRCRAFT DATA INDICATE
THAT THE LOW PRESSURE AREA OVER THE CENTRAL GULF OF MEXICO HAS
ACQUIRED A CLOSED CIRCULATION THAT IS DEFINED ENOUGH TO BE
CONSIDERED A TROPICAL DEPRESSION.  HOWEVER...THE CENTRAL REGION
STILL CONSISTS OF A LARGE AREA OF LIGHT WINDS.  THE AIRCRAFT DATA
AND BUOY OBSERVATIONS SUPPORT AN INITIAL INTENSITY OF 30 KT.
ALTHOUGH THERE IS WIND SHEAR OVER THE CYCLONE...AN UPPER-LEVEL
ANTICYCLONE IS FORECAST TO BUILD OVER THE GULF OF MEXICO DURING THE
NEXT DAY OR SO.  THIS SHOULD PROVIDE A MORE FAVORABLE UPPER-LEVEL
ENVIRONMENT FOR STRENGTHENING.  HOWEVER...SINCE THE CIRCULATION IS
LARGE ONLY GRADUAL STRENGTHENING IS ANTICIPATED.  THE OFFICIAL
INTENSITY FORECAST FOLLOWS THIS REASONING AND IS CLOSE TO THE
SHIPS/LGEM GUIDANCE.

SINCE THE DEPRESSION IS IN ITS FORMATIVE STAGE THE INITIAL MOTION
IS HIGHLY UNCERTAIN.  IN FACT...THE CENTER COULD REFORM WITHIN THE
LARGE CIRCULATION DURING THE NEXT 12-24 HOURS.   THE DEPRESSION IS
CURRENTLY LOCATED TO THE SOUTH OF A MID/UPPER LEVEL RIDGE OVER THE
CENTRAL UNITED STATES.  THE RIDGE IS FORECAST TO SLIDE EASTWARD AND
WEAKEN DURING THE NEXT 2-3 DAYS...LEAVING THE CYCLONE IN WEAK
STEERING FLOW.  THE OFFICIAL FORECAST SHOWS A SLOW NORTHWESTWARD
MOTION DURING THE NEXT 24 HOURS...FOLLOWED BY A TURN TOWARD THE
NORTH AND NORTHEAST.  THE NHC TRACK IS IN BEST AGREEMENT WITH THE
GFS AND ECMWF MODELS.

THE DEPRESSION IS EXPECTED TO MOVE VERY SLOWLY DURING THE NEXT 5
DAYS PROLONGING THE PERIOD OF TROPICAL STORM CONDITIONS AND HEAVY
RAINFALL OVER PORTIONS OF THE NORTHERN GULF COAST.

FORECAST POSITIONS AND MAX WINDS

INIT  02/0000Z 26.6N  91.4W   30 KT  35 MPH
12H  02/0600Z 27.5N  92.3W   35 KT  40 MPH
24H  02/1800Z 28.2N  92.6W   40 KT  45 MPH
36H  03/0600Z 28.7N  92.7W   45 KT  50 MPH
48H  03/1800Z 29.3N  92.6W   50 KT  60 MPH
72H  04/1800Z 30.1N  92.3W   40 KT  45 MPH...INLAND
96H  05/1800Z 31.1N  91.5W   30 KT  35 MPH...INLAND
120H  06/1800Z 32.0N  90.5W   25 KT  30 MPH...INLAND

$$
FORECASTER BROWN/AVILA