Tropical Depression TWELVE

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TROPICAL DEPRESSION TWELVE DISCUSSION NUMBER   1
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL   AL122007
1100 PM EDT MON SEP 24 2007
 
THE LARGE LOW PRESSURE AREA IN THE EASTERN ATLANTIC HAS ACQUIRED
ENOUGH ORGANIZATION TO BE CLASSIFIED AS A TROPICAL DEPRESSION.  A
2004 UTC QUIKSCAT OVERPASS WAS HELPFUL IN LOCATING THE CENTER OF
THE DEPRESSION AND THE QUIKSCAT DATA SUGGEST THAT THE MAXIMUM WINDS
WERE AROUND 25 KT AT THAT TIME.  SINCE THEN...DEEP CONVECTION
HAS INCREASED NEAR THE CENTER AND DVORAK CLASSIFICATIONS FROM TAFB
AND SAB SUPPORT TROPICAL STORM STRENGTH.  HOWEVER...THERE WAS SOME
SPREAD IN THE CENTER LOCATION OF THESE ESTIMATES...SO THE INITIAL
INTENSITY IS SET AT 30 KT.

THE INITIAL MOTION ESTIMATE IS 285/14. THE DEPRESSION IS EXPECTED TO
CONTINUE MOVING WEST-NORTHWESTWARD SOUTH OF A MID-LEVEL RIDGE OVER
THE CENTRAL AND EASTERN ATLANTIC DURING THE NEXT FEW DAYS.  A
WEAKNESS IN THE RIDGE IS FORECAST TO DEVELOP OVER THE CENTRAL
ATLANTIC IN 4 OR 5 DAYS...WHICH SHOULD ALLOW FOR A NORTHWESTWARD
TURN LATER IN THE FORECAST PERIOD.  THE DYNAMICAL MODEL GUIDANCE
GENERALLY AGREES ON THIS SCENARIO...BUT THERE IS SOME SPREAD IN
HOW FAR WEST THE CYCLONE WILL BE WHEN THE TURN MATERIALIZES.  THE
GFS...AND GFDL ARE FARTHER WEST...WHILE THE NOGAPS AND ECMWF ARE
ALONG THE EASTERN SIDE OF THE GUIDANCE.  THE OFFICIAL FORECAST IS
ALONG THE SOUTHERN SIDE OF THE GUIDANCE ENVELOPE AND LEANS CLOSER
TO THE GFS/GFDL SOLUTIONS.

THE INTENSITY FORECAST IS SOMEWHAT PROBLEMATIC.  THE DEPRESSION
APPEARS TO BE IN A FAVORABLE ENVIRONMENT FOR STRENGTHENING DURING
THE NEXT COUPLE OF DAYS.  THE SHIPS MODEL BRINGS THE DEPRESSION TO
HURRICANE STATUS IN 48 HOURS WHILE THE DYNAMICAL MODEL GUIDANCE IS
LESS AGGRESSIVE DURING THIS TIME FRAME.  BEYOND 72 HOURS...THE
GLOBAL MODELS INDICATE THAT SOUTH TO SOUTHWESTERLY SHEAR WILL
INCREASE...WHICH SHOULD HALT ADDITIONAL STRENGTHENING.  THE
OFFICIAL INTENSITY FORECAST IS MORE CONSERVATIVE THAN THE SHIPS
GUIDANCE AND IS CLOSER TO THE GFDL INTENSITY FORECAST.
 
FORECAST POSITIONS AND MAX WINDS
 
INITIAL      25/0300Z 10.1N  36.2W    30 KT
 12HR VT     25/1200Z 10.6N  38.4W    35 KT-
 24HR VT     26/0000Z 11.2N  41.4W    45 KT
 36HR VT     26/1200Z 11.8N  44.5W    50 KT
 48HR VT     27/0000Z 12.5N  47.4W    55 KT
 72HR VT     28/0000Z 15.3N  50.9W    60 KT
 96HR VT     29/0000Z 19.0N  53.0W    60 KT
120HR VT     30/0000Z 22.0N  54.5W    60 KT
 
$$
FORECASTER BROWN
 
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