631 
 WTNT44 KNHC 222039
 TCDAT4
  
 TROPICAL STORM ISAAC DISCUSSION NUMBER   7
 NWS NATIONAL HURRICANE CENTER MIAMI FL       AL092012
 500 PM AST WED AUG 22 2012
 
 SATELLITE...AIRCRAFT...RADAR...AND SURFACE OBSERVATIONS INDICATE
 THAT ISAAC HAS A BROAD CENTRAL AREA OF LIGHT WINDS WITH MULTIPLE
 VORTICITY MAXIMA EMBEDDED.  THE LOWEST PRESSURES ARE IN AN AREA
 NEAR GUADELOUPE...WHICH IS USED AS THE CURRENT CENTER SINCE IT HAS
 SOME CONTINUITY WITH THE CENTER PREVIOUSLY BEING TRACKED. 
 HOWEVER...THE MEAN CENTER IS LIKELY TO THE SOUTHEAST OF THE
 ADVISORY POSITION.  SOME ADJUSTMENT OF THE CENTER POSITION MAY BE
 NECESSARY WHEN THE CENTRAL CORE AGAIN CONSOLIDATES.  THE INITIAL
 INTENSITY IS HELD AT 40 KT...ALTHOUGH THE HURRICANE HUNTER AIRCRAFT
 DATA SUGGESTS THIS COULD BE GENEROUS.
  
 THE INITIAL MOTION IS NOW A SOMEWHAT UNCERTAIN 280/19.  OTHER THAN
 THE CENTER POSITION ISSUES...THERE IS NO SIGNIFICANT CHANGE TO THE
 FORECAST REASONING DURING THE FIRST 48 HR OF THE TRACK FORECAST. THE
 EAST-WEST ORIENTED SUBTROPICAL RIDGE TO THE NORTH OF ISAAC ALONG
 30N LATITUDE IS FORECAST BY ALL OF THE GLOBAL MODELS TO REMAIN
 INTACT ACROSS FLORIDA AND THE SOUTHEASTERN U.S. DURING THAT TIME. 
 THIS EARLY PART OF THE FORECAST TRACK IS SHIFTED A LITTLE TO THE
 SOUTH OF THE PREVIOUS FORECAST BASED ON THE OBSERVED POSITION AND
 MOTION.  AFTER 48 HR...THE RIDGE IS EXPECTED TO WEAKEN AS A
 MID/UPPER-LEVEL TROUGH MOVES ONTO THE EASTERN UNITED STATES.  THE
 GLOBAL MODELS HAVE COME INTO BETTER AGREEMENT SINCE THE LAST
 ADVISORY...WITH THE NOGAPS AND CANADIAN MODELS SHIFTING TO THE WEST
 AND THE ECMWF TO THE NORTH.  HOWEVER...THE ECMWF CONTINUES TO SHOW
 A STRONGER RIDGE...AND THUS SHOWS A MORE WESTERLY MOTION THAN THE
 OTHER MODELS.  THE 72-120 HR PORTION OF THE FORECAST TRACK IS
 SIMILAR TO THE PREVIOUS FORECAST AND LIES NEAR THE CONSENSUS
 MODELS.  THERE REMAINS CONSIDERABLE UNCERTAINTY AS TO WHICH PORTIONS
 OF FLORIDA...IF ANY...COULD BE AFFECTED BY ISAAC.
 
 WATER VAPOR IMAGERY AND MICROWAVE TOTAL PRECIPITABLE WATER DATA
 CONTINUE TO SHOW DRY AIR TO THE NORTHEAST OF ISAAC...AND A LACK OF
 CONVECTION IN THIS AREA SUGGESTS SOME OF THIS AIR IS ENTRAINING
 INTO THE CYCLONE AND DISRUPTING THE CONVECTIVE STRUCTURE.  GIVEN
 THE CURRENT STRUCTURE...THE NEW INTENSITY FORECAST CALLS FOR LITTLE
 CHANGE IN STRENGTH FOR THE NEXT 12 HR...FOLLOWED BY INTENSIFICATION
 INTO A HURRICANE BY 48 HR SIMILAR TO THE PREVIOUS ADVISORY.  AFTER
 48 HR...THE MAIN FACTOR CONTROLLING THE INTENSITY IS THE AMOUNT OF
 LAND INTERACTION.  THIS LOW-CONFIDENCE PART OF THE INTENSITY
 FORECAST IS SIMILAR TO THE PREVIOUS ADVISORY BUT ABOVE THE INTENSITY
 CONSENSUS.
 
  
 FORECAST POSITIONS AND MAX WINDS
  
 INIT  22/2100Z 16.0N  61.2W   40 KT  45 MPH
  12H  23/0600Z 16.3N  63.6W   40 KT  45 MPH
  24H  23/1800Z 16.7N  66.7W   50 KT  60 MPH
  36H  24/0600Z 17.2N  69.4W   60 KT  70 MPH
  48H  24/1800Z 17.9N  71.6W   70 KT  80 MPH...INLAND
  72H  25/1800Z 20.5N  75.5W   60 KT  70 MPH...INLAND
  96H  26/1800Z 23.5N  79.5W   60 KT  70 MPH...OVER WATER
 120H  27/1800Z 26.5N  82.5W   70 KT  80 MPH
  
 $$
 FORECASTER BEVEN