ZCZC MIATCDAT2 ALL TTAA00 KNHC DDHHMM TROPICAL DEPRESSION SEVEN DISCUSSION NUMBER 1 NWS NATIONAL HURRICANE CENTER MIAMI FL AL072011 1100 PM EDT SAT AUG 13 2011 SATELLITE IMAGERY INDICATES THAT THE LOW PRESSURE AREA SOUTH-SOUTHEAST OF BERMUDA HAS DEVELOPED PERSISTENT CENTRAL CONVECTION AROUND A TIGHTLY-WOUND LOW-LEVEL CENTER. SATELLITE INTENSITY ESTIMATES FROM SAB AND TAFB ARE 30 KT...AND BASED ON THESE ADVISORIES ARE INITIATED ON THE SYSTEM AS TROPICAL DEPRESSION SEVEN. THE INITIAL MOTION IS 290/9. THE DEPRESSION IS CURRENTLY ON THE SOUTHWEST SIDE OF A LARGE LOW-/MID-LEVEL RIDGE OVER THE CENTRAL NORTH ATLANTIC. A DEEP-LAYER TROUGH ADVANCING INTO THE THE EASTERN UNITED STATES AND THE NORTHWESTERN ATLANTIC WILL BREAK DOWN THE WESTERN END OF THE RIDGE...CAUSING THE DEPRESSION TO TURN NORTHWARD BY 36 HR AND RECURVE NORTHEASTWARD INTO THE WESTERLIES BY 72 HR. THE FORECAST TRACK FOLLOWS THIS SCENARIO...WITH THE FORECAST BEING A BLEND OF THE ECMWF AND GFDL MODEL FORECASTS. A POTENTIAL COMPLICATION TO THE TRACK FORECAST IS SHOWN BY THE UKMET MODEL... WHICH FORECASTS THE DEPRESSION TO EXPERIENCE ERRATIC MOTION DURING THE NEXT 48 HR AS IT INTERACTS WITH A DISTURBANCE CURRENTLY ABOUT 400 N MI TO THE SOUTHEAST. IF SUCH INTERACTION OCCURS...IT WOULD DELAY THE APPROACH OF THE DEPRESSION TO BERMUDA. WATER VAPOR IMAGERY SHOWS SMALL UPPER-LEVEL LOWS TO THE SOUTHWEST AND NORTHEAST OF THE DEPRESSION. THESE SYSTEMS ARE HELPING TO PRODUCE LIGHT NORTHWESTERLY VERTICAL WIND SHEAR...AS WELL AS ADVECTING UPPER-LEVEL DRY AIR INTO THE DEPRESSION. IN ADDITION... A LARGE PLUME OF AFRICAN DUST AND ASSOCIATED DRY AIR ARE APPROACHING THE DEPRESSION FROM THE EAST. WHILE VERTICAL SHEAR SHOULD BE LIGHT ENOUGH FOR THE NEXT 48 HR TO ALLOW DEVELOPMENT... THE ABUNDANT DRY AIR AROUND THE SYSTEM SHOULD AT LEAST SLOW INTENSIFICATION. THE INTENSITY FORECAST CALLS FOR GRADUAL STRENGTHENING THROUGH 48 HR WHILE THE CYCLONE REMAINS OVER WARM WATER. AFTER 72 HR...THE CYCLONE IS EXPECTED TO BE ABSORBED INTO A FRONTAL SYSTEM OVER THE FAR NORTH ATLANTIC. THE FORECAST TRACK AND WIND RADII REQUIRE A TROPICAL STORM WATCH FOR BERMUDA AT THIS TIME. A TROPICAL STORM WARNING WILL LIKELY BE REQUIRED SOMETIME ON SUNDAY. FORECAST POSITIONS AND MAX WINDS INIT 14/0300Z 27.9N 61.6W 30 KT 35 MPH 12H 14/1200Z 28.6N 62.6W 35 KT 40 MPH 24H 15/0000Z 30.1N 63.7W 40 KT 45 MPH 36H 15/1200Z 32.0N 64.0W 45 KT 50 MPH 48H 16/0000Z 35.0N 63.0W 50 KT 60 MPH 72H 17/0000Z 43.0N 55.0W 50 KT 60 MPH 96H 18/0000Z...ABSORBED BY FRONTAL SYSTEM $$ FORECASTER BEVEN NNNN
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