Tropical Depression SIX

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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
 
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