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#113315 (Received by flhurricane at: 4:40 AM 28.Sep.2006) TCDAT4 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 |