Hurricane IVO

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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
SIGNIFICANTLY.  THE OFFICIAL INTENSITY FORECAST IS A BIT ABOVE THE
CONSENSUS TECHNIQUE...ICON...BUT A LITTLE BELOW THE GFDL.
 
INTERESTS IN SOUTHERN BAJA CALIFORNIA SHOULD CLOSELY MONITOR THE
PROGRESS OF IVO DURING THE NEXT FEW DAYS. ONE SHOULD NOT FOCUS ON
THE EXACT TRACK AT 4 AND 5 DAYS BECAUSE THERE ARE LARGE
UNCERTAINTIES AT THESE FORECAST PERIODS.
 
 
FORECAST POSITIONS AND MAX WINDS
 
INITIAL      20/0900Z 16.5N 112.5W    65 KT
 12HR VT     20/1800Z 17.3N 113.0W    70 KT
 24HR VT     21/0600Z 18.3N 113.3W    75 KT
 36HR VT     21/1800Z 19.3N 113.1W    75 KT
 48HR VT     22/0600Z 20.3N 112.7W    70 KT
 72HR VT     23/0600Z 22.0N 111.5W    65 KT
 96HR VT     24/0600Z 23.5N 110.5W    55 KT
120HR VT     25/0600Z 25.5N 109.5W    50 KT
 
$$
FORECASTER MAINELLI/PASCH
 
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