Tropical Depression TWELVE

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TROPICAL DEPRESSION TWELVE DISCUSSION NUMBER   2
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL   AL122010
500 PM AST SUN SEP 12 2010
 
RECENT SATELLITE IMAGERY SHOWS AN INCREASE IN DEEP CONVECTION JUST
TO THE WEST OF THE ESTIMATED CENTER POSITION...HOWEVER THE INTENSITY
IS BEING HELD AT 30 KT FOR THIS ADVISORY BASED ON A BLEND OF DVORAK
ESTIMATES FROM TAFB AND SAB.  THE DEPRESSION IS STILL EXPERIENCING
SOME EASTERLY SHEAR...HOWEVER THE SHIPS MODEL FORECASTS THE SHEAR
TO WEAKEN IN THE NEXT 12 HOURS AND STAY BELOW 15 KT UNTIL 72 HOURS.
THE INTENSITY FORECAST IS UNCHANGED FROM THE PREVIOUS ADVISORY...
SHOWING STEADY STRENGTHENING THROUGH 48 HOURS IN BEST AGREEMENT WITH
THE SHIPS MODEL. AFTER THAT TIME...SEA SURFACE TEMPERATURES COOL
ALONG THE TRACK AND THE SHEAR INCREASES AS THE CYCLONE INTERACTS
WITH AN UPPER-LEVEL TROUGH/LOW AS INDICATED BY SEVERAL OF THE
GLOBAL MODELS.  GIVEN THE MIXED TRENDS IN THE GUIDANCE AT THIS TIME
PERIOD...THE OFFICIAL FORECAST WILL HOLD THE INTENSITY AT 65 KT
THROUGH DAY 5. 
 
THE CURRENT POSITION IS A LITTLE NORTH OF THE PREVIOUS TRACK...AND
THE INITIAL MOTION ESTIMATE IS 280 DEGREES AT 12 KT. THE OVERALL
THE SYNOPTIC REASONING REMAINS UNCHANGED.  A WEST-NORTHWESTWARD
TURN IS EXPECTED SOON AS THE DEPRESSION MOVES AROUND THE WESTERN
PERIPHERY OF THE SUBTROPICAL RIDGE OVER THE EASTERN ATLANTIC. THIS
MOTION IS EXPECTED CONTINUE THROUGH 36 TO 48 HOURS WHEN THE
DEPRESSION WILL TURN NORTHWESTWARD INTO A BREAK IN THE RIDGE. AT
DAYS 4 AND 5 A TURN BACK TOWARD THE WEST-NORTHWEST IS EXPECTED WITH
AN INCREASE IN FORWARD SPEED AS CYCLONE MOVES AROUND THE EASTERN
SIDE OF A UPPER-LEVEL LOW THAT CUTS OFF NEAR 40W. THE OFFICIAL NHC
FORECAST IS NORTH OF THE PREVIOUS ONE THROUGH 36 HOURS DUE TO THE
INITIAL POSITION AND MOTION...AND BEYOND THAT TIME IS BASICALLY AN
EXTENSION OF THE PREVIOUS ADVISORY.
 
FORECAST POSITIONS AND MAX WINDS
 
INITIAL      12/2100Z 13.3N  22.8W    30 KT
 12HR VT     13/0600Z 13.7N  24.6W    35 KT
 24HR VT     13/1800Z 14.6N  27.1W    45 KT
 36HR VT     14/0600Z 15.6N  29.0W    55 KT
 48HR VT     14/1800Z 16.9N  30.6W    65 KT
 72HR VT     15/1800Z 20.4N  34.2W    65 KT
 96HR VT     16/1800Z 24.0N  39.5W    65 KT
120HR VT     17/1800Z 27.1N  45.5W    65 KT
 
$$
FORECASTER BRENNAN
 
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