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| #110627 (Received by flhurricane at: 10:40 AM 13.Sep.2006) TCDAT3 TROPICAL DEPRESSION EIGHT DISCUSSION NUMBER 5 NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL AL082006 1100 AM EDT WED SEP 13 2006 MORNING VISIBLE IMAGERY INDICATES THAT TROPICAL DEPRESSION EIGHT REMAINS POORLY ORGANIZED...WITH THE CIRCULATION ELONGATED WEST-SOUTHWEST TO EAST-NORTHEAST AND SEVERAL VORTICITY MAXIMA ROTATING AROUND THE MEAN CENTER. SCATTERED CONVECTIVE CLUSTERS ARE PRESENT IN THE WESTERN SEMICIRCLE. SATELLITE INTENSITY ESTIMATES ARE 30 KT FROM ALL AGENCIES...AND THAT REMAINS THE INITIAL INTENSITY. THE INITIAL MOTION IS 270/15. THE DEPRESSION IS SOUTH OF A DEEP-LAYER RIDGE OVER THE EASTERN ATLANTIC...WHICH SHOULD KEEP THE SYSTEM MOVING GENERALLY WESTWARD FOR 24 HR OR SO. AFTER THAT...THE LARGE-SCALE MODELS FORECAST THE CYCLONE TO GRADUALLY TURN WEST-NORTHWESTWARD AND THEN NORTHWESTWARD TOWARD A WEAKNESS IN THE RIDGE NORTHEAST OF THE LESSER ANTILLES. ONE EXCEPTION TO THIS IS THE CANADIAN MODEL...WHICH IS A LEFT OUTLIER BRINGING THE CYCLONE TO JUST NORTHEAST OF THE LEEWARD ISLANDS BY 120 HR. THE NEW FORECAST TRACK FOLLOWS THE MAJORITY OF THE GUIDANCE IN CALLING FOR A NORTHWESTWARD MOTION BY 120 HR. THE NEW FORECAST TRACK IS A LITTLE TO THE LEFT OF THE MODEL CONSENSUS DUE TO A PAST TENDENCY OF THE LARGE-SCALE MODELS TO MOVE TROPICAL CYCLONES TOO FAR NORTH IN THIS SYNOPTIC PATTERN. THE CURRENT BROAD AND DISORGANIZED STRUCTURE SUGGESTS THAT SHORT-TERM INTENSIFICATION SHOULD BE SLOW. THUS...THE INTENSITY FORECAST TAKES 24 HR TO BRING THE DEPRESSION TO TROPICAL STORM STRENGTH. AFTER THAT...THE SYSTEM SHOULD STRENGTHEN AT A FASTER RATE IN A LIGHT VERTICAL SHEAR ENVIRONMENT...AND IT IS FORECAST TO BECOME A HURRICANE IN 72-96 HR. THERE ARE TWO COMPLICATING FACTORS IN THE INTENSITY FORECAST. THE FIRST IS DRY AIR PRESENT NORTH AND WEST OF THE CYCLONE. HOW MUCH OF THIS AIR WILL BE ENTRAINED INTO THE SYSTEM IS UNCLEAR AT THIS TIME. THE SECOND IS AN UPPER-LEVEL TROUGH FORECAST BY THE LARGE-SCALE MODELS TO THE NORTH OR NORTHEAST OF THE LESSER ANTILLES BY 120 HR. WHILE THE MODELS AGREE THE TROUGH WILL EXIST...THEY DO NOT AGREE ON THE LOCATION OR ON THE POSSIBLE IMPACT TO THE CYCLONE. FORECAST POSITIONS AND MAX WINDS INITIAL 13/1500Z 12.0N 28.5W 30 KT 12HR VT 14/0000Z 12.2N 30.7W 30 KT 24HR VT 14/1200Z 12.8N 34.0W 35 KT 36HR VT 15/0000Z 13.8N 37.0W 40 KT 48HR VT 15/1200Z 15.1N 39.6W 50 KT 72HR VT 16/1200Z 18.0N 43.5W 60 KT 96HR VT 17/1200Z 20.0N 46.5W 70 KT 120HR VT 18/1200Z 22.0N 49.5W 80 KT $$ FORECASTER BEVEN |
