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 513 
 WTNT42 KNHC 121455
 TCDAT2
 TROPICAL DEPRESSION TWELVE DISCUSSION NUMBER   1
 NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL   AL122010
 1100 AM AST SUN SEP 12 2010
  
 THE AREA OF LOW PRESSURE ASSOCIATED WITH A STRONG TROPICAL WAVE THAT
 MOVED OFF THE WEST COAST OF AFRICA YESTERDAY NOW HAS ENOUGH
 CONVECTIVE ORGANIZATION TO BE DECLARED A TROPICAL DEPRESSION.  THE
 INITIAL INTENSITY IS SET AT 30 KT BASED ON A BLEND OF DVORAK
 T-NUMBERS OF 2.5 AND 1.5 FROM TAFB AND SAB...RESPECTIVELY.
 THE DEPRESSION HAS A LARGE CURVED BAND IN THE WESTERN SEMICIRCLE
 ...AND OUTFLOW IS GOOD IN THAT PORTION OF THE CIRCULATION.
  
 ANALYSES FROM UW-CIMSS AND THE SHIPS MODEL SHOW ABOUT 10 KT OF
 EASTERLY SHEAR OVER THE CYCLONE...HOWEVER THE SHEAR IS EXPECTED TO
 DIMINISH IN THE NEXT 12 TO 24 HOURS. THE DEPRESSION WILL BE MOVING
 OVER WARM WATERS FOR THE NEXT COUPLE OF DAYS...AND STEADY
 INTENSIFICATION IS FORECAST.  BEYOND THAT TIME...THE CYCLONE WILL
 BE MOVING OVER MARGINAL SEA SURFACE TEMPERATURES...AND THE SHIPS
 MODEL SHOWS THE SHEAR INCREASING. THE STATISTICAL MODELS SHOW SOME
 WEAKENING AT DAYS 4 AND 5...BUT THE DYNAMICAL MODELS SHOW THEIR
 PEAK INTENSITY OF THE CYCLONE LATE IN THE PERIOD. AS A COMPROMISE
 ...THE OFFICIAL FORECAST SHOWS LITTLE CHANGE IN INTENSITY BEYOND 48
 HOURS. THE NHC FORECAST IS IN BEST AGREEMENT WITH THE LGEM THROUGH
 DAY 3 AND CLOSE TO ICON AT DAYS 4 AND 5.
  
 THE INITIAL MOTION ESTIMATE IS 275/12...AS THE DEPRESSION IS
 CURRENTLY LOCATED ON THE SOUTHWESTERN PERIPHERY OF A MID-LEVEL
 RIDGE THAT EXTENDS FROM NORTH AFRICA TO THE EASTERN ATLANTIC.  THE
 CYCLONE WILL TURN WEST-NORTHWESTWARD AND NORTHWESTWARD AND SLOW DOWN
 A LITTLE BY 48 HOURS AS IT APPROACHES A BREAK IN THE RIDGE TO THE
 SOUTHWEST OF A MID- AND UPPER-LEVEL LOW EAST OF THE AZORES. ON DAYS
 4 AND 5 THE MID- TO UPPER-LEVEL LOW MOVES EASTWARD.  THIS ALLOWS A
 MID-LEVEL RIDGE TO BUILD IN EAST AND NORTH OF THE CYCLONE...WHICH
 SHOULD RESULT IN AN ACCELERATION TOWARD THE NORTHWEST OR WEST-
 NORTHWEST BY THE END OF THE PERIOD.  THE OFFICIAL FORECAST IS CLOSE
 TO A BLEND OF ALL THE DYNAMICAL MODELS...WITH THE EXCEPTION OF THE
 NOGAPS...WHICH APPEARS TO BE A SOUTHERLY OUTLIER.
  
 FORECAST POSITIONS AND MAX WINDS
  
 INITIAL      12/1500Z 12.7N  21.4W    30 KT
  12HR VT     13/0000Z 12.8N  23.3W    35 KT
  24HR VT     13/1200Z 13.5N  25.5W    45 KT
  36HR VT     14/0000Z 14.5N  27.7W    55 KT
  48HR VT     14/1200Z 15.7N  29.4W    65 KT
  72HR VT     15/1200Z 19.0N  32.5W    65 KT
  96HR VT     16/1200Z 23.0N  37.0W    65 KT
 120HR VT     17/1200Z 26.5N  43.0W    65 KT
  
 $$
 FORECASTER BRENNAN
  
 
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