Tropical Depression NINE

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TROPICAL DEPRESSION NINE DISCUSSION NUMBER   3
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL   AL092006
500 AM EDT THU SEP 28 2006
 
SATELLITE IMAGES SHOW THAT THE CENTER OF TROPICAL DEPRESSION NINE
REMAINS MOSTLY EXPOSED TO THE SOUTHEAST OF THE MAIN CONVECTIVE
AREA.  SATELLITE INTENSITY ESTIMATES ARE 35 KT FROM TAFB AND
SAB...AND 30 KT FROM AFWA.  SINCE THE CENTER IS STILL EXPOSED AND
THE CONVECTIVE TOPS ARE CURRENTLY WARMING...THE SYSTEM WILL REMAIN
A DEPRESSION FOR THIS ADVISORY.  THE CENTER SHOULD PASS NEAR A
DRIFTING BUOY DURING THE NEXT FEW HOURS...WHICH SHOULD PRODUCE A
BETTER ESTIMATE OF THE CENTRAL PRESSURE.  ALSO...QUIKSCAT DATA
SHOULD BE AVAILABLE IN THE NEXT FEW HOURS.

THE INITIAL MOTION IS 315/10.  WATER VAPOR IMAGERY SHOWS THAT THE
DEPRESSION IS SOUTHWEST OF A MID/UPPER-LEVEL RIDGE OVER THE CENTRAL
ATLANTIC...WITH A MID/UPPER-LEVEL LOW NEAR 27N58W.  WEST OF THAT...
BROAD DEEP-LAYER TROUGHING COVERS THE WESTERN ATLANTIC AND THE
EASTERN UNITED STATES.  IN THE SHORT TERM...FLOW BETWEEN THE
ATLANTIC RIDGE AND LOW SHOULD MOVE THE DEPRESSION GENERALLY
NORTHWESTWARD.  AFTER 24-36 HR...THE LARGE-SCALE MODELS FORECAST
THE WESTERN ATLANTIC TROUGH TO AMPLIFY...WHICH IN TURN SHOULD RAISE
HEIGHTS NORTH OF THE DEPRESSION.  THIS SHOULD RESULT IN A SLOWER
FORWARD MOTION...AND POSSIBLY A MORE WESTWARD TURN AS FORECAST BY
THE GFS AND GFDL. AFTER 60 HR...THE WESTERN ATLANTIC TROUGH AND
ASSOCIATED SURFACE LOW WILL GET CLOSE ENOUGH TO THE DEPRESSION TO
RECURVE IT NORTHEASTWARD.  THE TRACK GUIDANCE IS NOTABLY SLOWER
THAN FOR THE PREVIOUS ADVISORY DURING THE FIRST 72 HR...AND THUS
THE NEW FORECAST TRACK IS SLOWED DOWN AS WELL.  THE NEW TRACK IS
ALSO A LITTLE TO THE LEFT OF THE PREVIOUS TRACK.

THE UPPER LOW IS CURRENTLY CAUSING SOUTHERLY VERTICAL SHEAR OVER THE
DEPRESSION.  THE LARGE-SCALE MODELS FORECAST THAT THE SHEAR SHOULD
DECREASE DURING THE NEXT 48 HR AS THE CYCLONE MOVES NORTH OF THE
UPPER LOW.  THIS SHOULD ALLOW FOR SOME STRENGTHENING AS SHOWN BY
THE GFDL MODEL...WHICH IS REFLECTED IN THE INTENSITY FORECAST.  DUE
TO INTERACTION WITH THE UPPER LOW...THERE IS A POSSIBILITY THE
CYCLONE COULD ACQUIRE SOME SUBTROPICAL CHARACTERISTICS AS IT
DEVELOPS.  AFTER 48 HR...THE CYCLONE SHOULD ENCOUNTER COOLER WATER
AND INCREASING SOUTHWESTERLY UPPER-LEVEL FLOW ASSOCIATED WITH THE
DEEP-LAYER TROUGH.  THIS SHOULD CAUSE WEAKENING...AND EVENTUALLY
LEAD TO EXTRATROPICAL TRANSITION IN 96-120 HR.
 
FORECAST POSITIONS AND MAX WINDS
 
INITIAL      28/0900Z 27.8N  54.6W    30 KT
 12HR VT     28/1800Z 28.8N  55.7W    35 KT
 24HR VT     29/0600Z 30.0N  56.7W    40 KT
 36HR VT     29/1800Z 31.1N  57.7W    45 KT
 48HR VT     30/0600Z 32.3N  58.4W    50 KT
 72HR VT     01/0600Z 36.5N  58.5W    50 KT
 96HR VT     02/0600Z 42.0N  54.0W    50 KT...BECOMING EXTRATROPICAL
120HR VT     03/0600Z 47.0N  46.0W    50 KT...EXTRATROPICAL
 
$$
FORECASTER BEVEN
 
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