Tropical Depression THIRTEEN

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TROPICAL DEPRESSION THIRTEEN DISCUSSION NUMBER   1
NWS NATIONAL HURRICANE CENTER MIAMI FL       AL132012
500 PM EDT MON SEP 03 2012
 
THE SMALL LOW PRESSURE SYSTEM LOCATED OVER THE CENTRAL
ATLANTIC...WHICH DEVELOPED FROM AN UPPER-LEVEL TROUGH...HAS
GRADUALLY ACQUIRED ENOUGH ORGANIZED DEEP CONVECTION TO BE
CLASSIFIED AS A TROPICAL DEPRESSION. VISIBLE SATELLITE IMAGERY AND
AN EARLIER ASCAT PASS INDICATED THAT THE LOW HAS A WELL-DEFINED
CENTER AND RELIABLE WINDS OF AROUND 25 KT. THE INITIAL INTENSITY IS
SET A LITTLE HIGHER AT 30 KT SINCE ASCAT HAS A KNOWN LOW BIAS AND
BECAUSE THE RESOLUTION OF THE INSTRUMENT LIKELY CAN NOT RESOLVE THE
SMALL RADIUS OF MAXIMUM WINDS.
 
THE DEPRESSION CURRENTLY LIES BENEATH A TROUGH AXIS...WHERE THE
UPPER-LEVEL WINDS APPEAR RELATIVELY LIGHT. GLOBAL MODELS SHOW THE
TROUGH AND THE CYCLONE MOVING IN TANDEM...WHICH KEEPS THE
DEPRESSION IN A MARGINALLY FAVORABLE UPPER-LEVEL WIND PATTERN FOR A
DAY OR SO. THEREFORE...SOME SLIGHT STRENGTHENING IS SHOWN IN THE
SHORT TERM. BY LATE WEDNESDAY...THE TROUGH IS EXPECTED TO LIFT OUT
AND WEAKEN. THIS WILL CAUSE AN INCREASE IN NORTHWESTERLY
SHEAR...AND WILL LIKELY RESULT IN WEAKENING. THE SYSTEM IS 
EXPECTED TO DEGENERATE TO A REMNANT LOW IN A FEW DAYS.

THE DEPRESSION IS FORECAST TO MOVE SLOWLY WEST-NORTHWESTWARD AROUND
THE SOUTHWESTERN PORTION OF A RIDGE OVER THE EASTERN ATLANTIC
DURING THE NEXT 24 HOURS.  AFTER THAT TIME...THE CYCLONE IS
EXPECTED TO TURN NORTHWARD AS THE WESTERN PORTION OF THE RIDGE
ERODES.  
 
FORECAST POSITIONS AND MAX WINDS
 
INIT  03/2100Z 25.6N  42.2W   30 KT  35 MPH
 12H  04/0600Z 25.8N  42.9W   35 KT  40 MPH
 24H  04/1800Z 26.4N  43.7W   35 KT  40 MPH
 36H  05/0600Z 27.3N  44.3W   35 KT  40 MPH
 48H  05/1800Z 28.0N  44.5W   30 KT  35 MPH
 72H  06/1800Z 28.5N  44.5W   25 KT  30 MPH...POST-TROP/REMNT LOW
 96H  07/1800Z 29.5N  44.5W   20 KT  25 MPH...POST-TROP/REMNT LOW
120H  08/1800Z 30.5N  44.5W   20 KT  25 MPH...POST-TROP/REMNT LOW
 
$$
FORECASTER BROWN/CANGIALOSI
 
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