135 
 WTNT44 KNHC 060838
 TCDAT4
 TROPICAL STORM COLIN DISCUSSION NUMBER  10
 NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL   AL042010
 500 AM AST FRI AUG 06 2010
  
 VERTICAL WIND SHEAR...ANALYZED AT 25 KT BY THE SHIPS MODEL...HAS
 AGAIN TAKEN A TOLL ON COLIN...WITH THE LOW-LEVEL CENTER NOW
 COMPLETELY EXPOSED TO THE WEST OF THE PULSING DEEP CONVECTION.  AN
 ASCAT PASS AROUND 0118 UTC SHOWED SEVERAL 35-40 KT RETRIEVALS EAST
 OF THE CENTER...AND THE INITIAL INTENSITY IS LOWERED TO 40 KT FOR
 THIS ADVISORY.  THE SHIPS MODEL SHOWS THE SHEAR DECREASING TO LESS
 THAN 10 KT IN 24 HOURS...WHICH SHOULD GIVE COLIN AN OPPORTUNITY TO
 RE-INTENSIFY.  HOWEVER...THE SHEAR INCREASES RAPIDLY AGAIN BY 48
 HOURS...WHICH SHOULD LIMIT INTENSIFICATION BEYOND THAT TIME. THE
 OFFICIAL INTENSITY FORECAST IS ADJUSTED DOWNWARD TOWARD THE ICON
 INTENSITY CONSENSUS THROUGH 48 HOURS AND IS SIMILAR TO THE PREVIOUS
 PACKAGE AFTER THAT.
  
 THE 12-HOUR INITIAL MOTION ESTIMATE IS 325/12...TO THE LEFT OF THE
 PREVIOUS TRACK FORECAST. COLIN IS SITUATED TO THE SOUTHEAST OF AN
 UPPER-LEVEL SHEAR AXIS ANCHORED BY ONE LOW CENTER NEAR 27N 75W AND
 ANOTHER NEAR BERMUDA.  THE GLOBAL MODELS SUGGEST THAT THESE LOWS
 WILL MOVE AWAY AND ALLOW COLIN TO MOVE NORTHWARD AT A SLOWER SPEED
 INTO A BREAK IN THE SUBTROPICAL RIDGE OVER THE NEXT COUPLE OF DAYS.
 BEYOND THAT TIME...THE GLOBAL MODELS SHOW A LONGWAVE TROUGH
 ADVANCING EASTWARD ACROSS THE NORTHEASTERN U.S. AND EASTERN
 CANADA.  HOWEVER...THE TIMING OF THE INTERACTION BETWEEN COLIN AND
 INDIVIDUAL SHORTWAVES IN THE TROUGH VARIES WIDELY IN THE
 GUIDANCE...AND SO DOES THE FORWARD SPEED AND TRACK OF THE CYCLONE.
 THE GFS...ECMWF...AND GFDL MOVE COLIN MORE SLOWLY AND DELAY
 INTERACTION WITH THE TROUGH UNTIL AROUND DAY 4...WHILE THE UKMET...
 NOGAPS...AND HWRF TAKE COLIN MORE QUICKLY NORTHWARD AND SHOW
 INTERACTION WITH THE TROUGH ABOUT A DAY EARLIER. GIVEN THAT
 THE 72-HOUR FORECAST POSITIONS FROM THE GFS AND NOGAPS ARE ABOUT
 1000 MILES APART...THIS TRACK FORECAST HAS LOW CONFIDENCE...
 ESPECIALLY IN THE LATER PERIODS.  THE OFFICIAL FORECAST HAS BEEN
 ADJUSTED TO THE LEFT OF THE PREVIOUS NHC TRACK THROUGH 48 HOURS DUE
 TO THE MORE WESTERLY INITIAL POSITION AND MOTION...AND LIES ALONG
 THE LEFT SIDE OF THE GUIDANCE ENVELOPE. BEYOND THAT TIME...THE
 BIGGEST CHANGE TO THE OFFICIAL FORECAST WAS TO SLIGHTLY DECREASE THE
 FORWARD SPEED DUE TO THE LARGE SPREAD IN THE GUIDANCE. ONE
 ALTERNATIVE SCENARIO IS THAT IF COLIN REMAINS A SHALLOW SYSTEM
 WITHOUT MUCH DEEP CONVECTION...IT COULD MOVE FARTHER TO THE LEFT
 AND MORE SLOWLY IN THE SHORT TERM ALONG A TRACK SIMILAR TO THE
 SHALLOW BAM.
  
 FORECAST POSITIONS AND MAX WINDS
  
 INITIAL      06/0900Z 26.8N  67.4W    40 KT
  12HR VT     06/1800Z 27.9N  67.7W    40 KT
  24HR VT     07/0600Z 29.8N  67.4W    45 KT
  36HR VT     07/1800Z 31.5N  66.8W    50 KT
  48HR VT     08/0600Z 33.6N  65.7W    55 KT
  72HR VT     09/0600Z 38.5N  62.5W    60 KT
  96HR VT     10/0600Z 44.0N  56.0W    55 KT
 120HR VT     11/0600Z 50.5N  45.0W    50 KT...POST-TROP/EXTRATROP
  
 $$
 FORECASTER BRENNAN