Tropical Depression SEVENTEEN

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TROPICAL DEPRESSION SEVENTEEN DISCUSSION NUMBER   2
NWS NATIONAL HURRICANE CENTER MIAMI FL       AL172011
1100 AM EDT SAT SEP 24 2011

AFTER AN EARLIER INCREASE IN DEEP CONVECTION AND BANDING
FEATURES...THE CONVECTIVE ORGANIZATION OF THE DEPRESSION HAS
DECREASED A LITTLE SINCE THE 12Z FIXES. INTENSITY ESTIMATES ARE 
T2.8/41 KT FROM UW-CIMSS ADT...T2.5/35 KT FROM TAFB...AND T1.5/25
KT FROM SAB. HOWEVER...THE CURVED BAND TO THE NORTH OF CENTER HAS
FRACTURED AND DEGENERATED AND THE ADT ESTIMATES ARE BASED ON AN
UNREPRESENTATIVE SHEAR PATTERN. AS A RESULT...THE INITIAL INTENSITY
WILL REMAIN AT 30 KT FOR THIS ADVISORY...WHICH IS CONSISTENT WITH
SEVERAL 30-KT WIND VECTORS NOTED IN A 1058Z ASCAT OVERPASS.

THE INITIAL MOTION ESTIMATE IS 285/14. THE CYCLONE IS EXPECTED TO
MOVE IN A GENERAL WEST-NORTHWESTWARD MOTION FOR THE NEXT 3 DAYS OR
SO UNDER THE INFLUENCE OF A STRONG SUBTROPICAL RIDGE ORIENTED
EAST-WEST ALONG 20N LATITUDE. HOWEVER...BY 72 HOURS A BREAK IN THE
RIDGE IS FORECAST TO DEVELOP BETWEEN 40-45W LONGITUDE AS A BROAD
LOW PRESSURE TROUGH DIGS SOUTHEASTWARD OVER THE EASTERN ATLANTIC.
THIS SHOULD RESULT IN THE CYCLONE SLOWING DOWN AND TURNING TOWARD
THE NORTHWEST INTO THE WEAKNESS. THE OFFICIAL FORECAST IS JUST AN
EXTENSION OF THE PREVIOUS ADVISORY TRACK AND LIES CLOSE TO THE
CONSENSUS MODELS TVCN AND TVCA.
 
ENVIRONMENTAL CONDITIONS WILL BE MAXIMIZED DURING THE NEXT 48 HOURS
OR SO FOR INTENSIFICATION TO OCCUR OVER THE NEXT COUPLE OF DAYS.
AFTER THAT...VERTICAL SHEAR IS EXPECTED TO INCREASE...ALBEIT TO
ONLY ABOUT 15 KT...FROM THE SOUTHWEST AHEAD OF THE AFOREMENTIONED
MID/UPPER-LEVEL TROUGH. THIS IS EXPECTED TO RESULT IN A SLOWER RATE
OF INTENSIFICATION.  THE OFFICIAL INTENSITY FORECAST REMAINS ON THE
CONSERVATIVE SIDE OF THE INTENSITY GUIDANCE ENVELOPE AND FOLLOWS A
BLEND OF THE SHIPS AND LGEM MODELS.

FORECAST POSITIONS AND MAX WINDS
 
INIT  24/1500Z 11.0N  26.7W   30 KT  35 MPH
 12H  25/0000Z 11.4N  28.3W   35 KT  40 MPH
 24H  25/1200Z 12.2N  30.5W   40 KT  45 MPH
 36H  26/0000Z 13.2N  32.3W   50 KT  60 MPH
 48H  26/1200Z 14.2N  33.8W   60 KT  70 MPH
 72H  27/1200Z 16.4N  36.1W   60 KT  70 MPH
 96H  28/1200Z 18.4N  38.1W   55 KT  65 MPH
120H  29/1200Z 20.5N  39.5W   50 KT  60 MPH
 
$$
FORECASTER STEWART
 
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