585 
 WTPZ42 KNHC 191450
 TCDEP2
 TROPICAL STORM IVO DISCUSSION NUMBER   5
 NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL   EP122007
 800 AM PDT WED SEP 19 2007
 
 SATELLITE IMAGERY THIS MORNING SHOWS THAT IVO HAS A SOMEWHAT RAGGED
 CENTRAL DENSE OVERCAST WITH CLOUD TOPS OF -70C TO -80C.  SATELLITE
 INTENSITY ESTIMATES ARE 55 KT FROM TAFB AND SAB...SO THE INITIAL
 INTENSITY IS INCREASED TO 55 KT.  THE CIRRUS OUTFLOW REMAINS GOOD
 IN THE SOUTHEASTERN SEMICIRCLE...BUT HAS DECREASED A LITTLE OVER
 THE NORTHWESTERN SEMICIRCLE.
  
 THE INITIAL MOTION IS 295/10.  IVO REMAINS SOUTH OF A MID-LEVEL
 RIDGE EXTENDING WESTWARD FROM NORTHERN MEXICO.  THE LARGE-SCALE
 MODELS ARE IN GOOD AGREEMENT THAT A DEEP-LAYER LOW CURRENTLY MOVING
 SOUTHWARD INTO CALIFORNIA WILL DROP FAR ENOUGH SOUTH TO BREAK THE
 RIDGE NORTH OF IVO...ALLOWING THE STORM TO RECURVE TO THE NORTHEAST
 DURING THE NEXT 72-96 HR.  HOWEVER...IT APPEARS THE LOW WILL NOT
 COME FAR ENOUGH SOUTH TO ACCELERATE THE STORM NORTHEASTWARD...SO
 THE MOTION AFTER RECURVATURE IS LIKELY TO BE SLOW.  THE NEW TRACK
 FORECAST IS AN UPDATE OF THE PREVIOUS TRACK FOR THE FIRST 72 HR...
 THEN IS SHIFTED TO THE NORTHEAST AT 96 AND 120 HR IN A COMPROMISE
 BETWEEN THE GFDL...HWRF...UKMET...AND FSU SUPERENSEMBLE MODELS.  IT
 SHOULD BE NOTED THAT WHILE THE LARGE-SCALE MODELS AGREE ON THE
 EVOLUTION OF THE STEERING PATTERNS...THEY DO NOT AGREE ON THE
 MOTION.  THE GFS AND ECMWF BOTH SHOW IVO INTERACTING WITH ANOTHER
 DISTURBANCE TO THE WEST WHICH PREVENTS THE STORM FROM RECURVING IN
 THOSE MODELS.
 
 IVO IS FORECAST TO REMAIN IN A LIGHT VERTICAL WIND SHEAR ENVIRONMENT
 FOR THE NEXT 36 HR OR SO...SO CONTINUED STRENGTHENING IS FORECAST
 IN AGREEMENT WITH THE SHIPS MODEL.  BEYOND THAT TIME...THE
 LARGE-SCALE MODELS DISAGREE ON HOW MUCH WIND SHEAR IVO WILL
 ENCOUNTER.  THE SHIPS AND GFDL MODELS FORECAST 20-25 KT OF
 NORTHWESTERLY SHEAR...WHILE THE OTHER GLOBAL MODELS SHOW LESS
 SHEAR.  FOR NOW...THE INTENSITY FORECAST WILL FOLLOW SHIPS AND CALL
 FOR GRADUAL WEAKENING AFTER 48 HR.  HOWEVER...THERE ARE TWO
 ALTERNATIVES.  FIRST...THE NEW FORECAST TRACK BRINGS IVO OVER
 WARMER WATER BY 120 HR...AND IF THE GFS IS WRONG ABOUT THE AMOUNT
 OF SHEAR IVO COULD BE STRONGER THAN FORECAST AT THAT TIME. 
 SECOND...IF IVO TRACKS NORTH OF THE FORECAST TRACK...IT WOULD
 LIKELY ENCOUNTER BOTH STRONGER SHEAR AND COLDER WATER...WHICH
 SHOULD CAUSE A FASTER WEAKENING.
 
 FORECAST POSITIONS AND MAX WINDS
  
 INITIAL      19/1500Z 15.3N 111.1W    55 KT
  12HR VT     20/0000Z 15.9N 112.1W    65 KT
  24HR VT     20/1200Z 16.8N 113.2W    70 KT
  36HR VT     21/0000Z 17.7N 113.9W    75 KT
  48HR VT     21/1200Z 18.6N 114.0W    75 KT
  72HR VT     22/1200Z 20.5N 113.0W    70 KT
  96HR VT     23/1200Z 21.5N 111.5W    60 KT
 120HR VT     24/1200Z 22.0N 110.0W    55 KT
  
 $$
 FORECASTER BEVEN