ZCZC MIATCDAT1 ALL TTAA00 KNHC DDHHMM TROPICAL DEPRESSION SIX DISCUSSION NUMBER 4 NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL AL062006 1100 AM EDT MON SEP 04 2006 VISIBLE SATELLITE IMAGES INDICATE THE DEPRESSION IS NEARING STORM STRENGTH. CURVED BANDS ARE BECOMING MORE PROMINENT IN THE NORTHWEST QUADRANT AND EASTERN SEMICIRCLE OF THE DEPRESSION...THOUGH THESE BANDS ARE STILL SOMEWHAT FAR FROM THE CENTER. A QUIKSCAT PASS OVER THE DEPRESSION AT 0901 UTC SHOWS THAT THERE ARE PLENTY OF 25 TO 30 KT WINDS IN THE CIRCULATION... AND A SMALL AREA OF POSSIBLY RAIN-INFLATED 35 KT VECTORS. ALTHOUGH SATELLITE INTENSITY ESTIMATES ARE AT MINIMAL STORM STRENGTH... QUIKSCAT IS NOT CLEARLY SUPPORTIVE OF SUCH AN INTENSITY AND WITH THE CONVECTION REMAINING A LITTLE THIN... THE INITIAL INTENSITY WILL STAY 30 KT. MODERATE SOUTHWESTERLY SHEAR ASSOCIATED WITH A RATHER DEEP TROUGH OVER THE CENTRAL ATLANTIC SHOULD PERSIST FOR THE NEXT COUPLE OF DAYS. THIS SHOULD ALLOW FOR ONLY A SLOW STRENGTHENING THROUGH WEDNESDAY. THEREAFTER... THE TAIL END OF THE UPPER TROUGH IS FORECAST BY ALMOST ALL OF THE GLOBAL MODELS TO FRACTURE... LEAVING AN UPPER-LEVEL LOW BEHIND... TO THE WEST OF THE STORM. THIS UPPER LOW SHOULD MOVE WESTWARD AWAY FROM THE SYSTEM... AND IN ITS WAKE GLOBAL MODELS RESPOND BY BUILDING A LARGE UPPER-LEVEL ANTICYCLONE OVER THE STORM. THESE CONDITIONS COULD ALLOW FOR MORE STRENGTHENING THAN SHOWN TOWARDS THE END OF THE FORECAST PERIOD. FOR NOW A BLEND OF THE GFDL AND SHIPS WILL BE USED...WHICH RESULTS IN LITTLE CHANGE TO THE OFFICIAL FORECAST. RECENT VISIBLE IMAGES REQUIRE A WESTWARD RELOCATION OF THE DEPRESSION BY ABOUT 60 MILES... GIVING A LONGER-TERM AVERAGE MOTION OF 305/10. THE LARGE MIDDLE TO UPPER-LEVEL TROUGH THAT HAS BEEN SHEARING THE SYSTEM IS ALSO RESPONSIBLE FOR WEAKENING THE RIDGE TO THE NORTH... CAUSING THE NORTHWESTWARD MOTION. THE MIDDLE TROPOSPHERIC PORTION OF THE TROUGH IS FORECAST TO PULL OUT IN ABOUT 48 HOURS... AND SHOULD ALLOW A WESTWARD TURN AROUND THAT TIME. THE TRACK FORECAST HAS BEEN SHIFTED A LITTLE FARTHER SOUTH...SOMEWHAT TO REFLECT THE CENTER RELOCATION... BUT IS STILL NORTH OF MOST OF THE GLOBAL MODELS IN THE FIRST FEW DAYS OF THE FORECAST. TOWARD THE END OF THE FORECAST... A WEST TO WEST-NORTHWEST TRACK SEEMS MOST LIKELY WITH A STRONG RIDGE FORECAST OVER THE CENTRAL ATLANTIC. SOME MODELS SLOW THE SYSTEM DOWN SIGNIFICANTLY IN THE EXTENDED PERIOD... WHICH IS A LITTLE PUZZLING GIVEN THE STRONG RIDGING. WE'VE OPTED TO BE AHEAD OF THE MODEL CONSENSUS BUT STILL SLOWER THAN THE GFS/GFDL/GFS ENSEMBLE MEAN. FORECAST POSITIONS AND MAX WINDS INITIAL 04/1500Z 16.3N 42.7W 30 KT 12HR VT 05/0000Z 17.0N 44.0W 35 KT 24HR VT 05/1200Z 17.8N 45.6W 40 KT 36HR VT 06/0000Z 18.5N 47.1W 45 KT 48HR VT 06/1200Z 19.2N 48.9W 50 KT 72HR VT 07/1200Z 20.0N 52.0W 60 KT 96HR VT 08/1200Z 21.0N 55.5W 70 KT 120HR VT 09/1200Z 22.0N 59.0W 75 KT $$ FORECASTER BLAKE/FRANKLIN NNNN
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Page last modified: Monday, 11-Sep-2006 11:28:37 UTC