284 
 WTPZ42 KNHC 200834
 TCDEP2
 HURRICANE IVO DISCUSSION NUMBER   8
 NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL   EP122007
 200 AM PDT THU SEP 20 2007
  
 CONVENTIONAL SATELLITE IMAGERY SHOWS THAT IVO HAS MAINTAINED ITS
 DEEP CONVECTION AND UPPER-LEVEL OUTFLOW....AND RECENT MICROWAVE
 PASSES FROM BOTH SSM/I AND AMSU-B INDICATE AN EYE FEATURE.  AN
 EARLIER QUIKSCAT PASS AT 0136 UTC HAD MAXIMUM WIND VECTORS OF AT
 LEAST 55 KT.  THESE VECTORS WERE LIKELY ATTENUATED BY HEAVY
 RAIN...SO THE ACTUAL MAXIMUM WINDS WERE PROBABLY CLOSER TO 65 KT. 
 DVORAK INTENSITY ESTIMATES FROM TAFB AND SAB REMAIN AT 4.0 OR 65
 KT...WHICH IS USED FOR THE INITIAL INTENSITY.  THE 34- AND 50-KT
 WIND RADII HAVE BEEN ADJUSTED BASED ON THE QUIKSCAT PASS. 
  
 IVO IS MOVING A BIT TO THE RIGHT OF THE PREVIOUS TRACK...AND THE
 INITIAL MOTION IS NOW ESTIMATED AT 330/6.  THE FORWARD MOTION HAS
 SLOWED AS THE HURRICANE MAKES ITS WAY AROUND THE WESTERN PERIPHERY
 OF THE SUBTROPICAL RIDGE.  A SLOW NORTHWARD MOTION IS ANTICIPATED
 FOR THE NEXT 36 HOURS OR SO.  THEREAFTER A MID-LATITUDE TROUGH IS
 EXPECTED TO DIG SOUTHEASTWARD NEAR THE SOUTHERN CALIFORNIA-NORTHERN
 BAJA CALIFORNIA BORDER.  THIS STEERING FEATURE SHOULD CREATE A MORE
 NORTH-NORTHEASTWARD TO NORTHEASTWARD MOTION IN THE LATER PERIODS.
 SOME OF THE DYNAMICAL MODELS SUCH AS THE GFS AND HWRF SUGGEST THAT
 IVO WILL WEAKEN AND TAKE A MORE NORTHWARD OR EVEN NORTHWESTWARD
 TRACK NEAR THE END OF THE PERIOD.  THE OFFICIAL TRACK FORECAST IS
 CLOSER TO THE GFDL SCENARIO OF A STRONGER SYSTEM THAT WILL BE MORE
 RESPONSIVE TO THE TROUGH.  THIS IS SIMILAR TO THE PREVIOUS OFFICIAL
 FORECAST.
  
 THE HURRICANE IS CURRENTLY IN A FAVORABLE ENVIRONMENT FOR ADDITIONAL
 STRENGTHENING...WITH WARM WATERS AND RELATIVELY WEAK SHEAR.  BOTH OF
 THESE ENVIRONMENTAL CONDITIONS ARE EXPECTED TO CONTINUE TO PREVAIL
 FOR THE NEXT COUPLE OF DAYS.  THE INTENSITY FORECAST IN THE LATER
 PERIODS IS HIGHLY UNCERTAIN.  IF IVO TRACKS SLIGHTLY TO THE NORTH OF
 OUR FORECAST...STRONGER SHEAR COULD CAUSE THE CYCLONE TO WEAKEN
 SIGNIFIC