174 
 WTNT44 KNHC 232055
 TCDAT4
  
 TROPICAL STORM ISAAC DISCUSSION NUMBER  11
 NWS NATIONAL HURRICANE CENTER MIAMI FL       AL092012
 500 PM AST THU AUG 23 2012
 
 LOCATING THE CENTER OF ISAAC IS A BIT PROBLEMATIC THIS AFTERNOON. 
 WHILE THE CYCLONE HAS A LARGE AND WELL-DEFINED OUTER
 CIRCULATION...THE INNER CORE HAS NOT CONSOLIDATED AND THERE ARE
 STILL MULTIPLE VORTICITY CENTERS ROTATING AROUND THE MEAN CENTER. 
 HIGHLIGHTING THE ISSUE ARE DATA FROM NOAA BUOY 42059...WHICH HAS
 REPORTED 25-30 KT SOUTHWESTERLY WINDS AT A POSITION SOUTHWEST OF
 THE LATEST HURRICANE HUNTER AIRCRAFT FIXES...WHICH IN TURN WERE
 SOUTH OF THE CENTER TRACKED IN THE PREVIOUS ADVISORY.  THE INITIAL
 POSITION IS A BLEND OF ALL THESE FEATURES.  THE INITIAL INTENSITY
 REMAINS 35 KT BASED ON THE HURRICANE HUNTER DATA.
 
 THE SOMEWHAT UNCERTAIN INITIAL MOTION IS 285/14.  THE TRACK MODEL
 GUIDANCE IS IN GOOD AGREEMENT THAT ISAAC SHOULD MOVE GENERALLY
 WEST-NORTHWESTWARD FOR THE NEXT 48-72 HR...AND THIS PART OF THE NEW
 FORECAST TRACK IS VERY SIMILAR TO THE PREVIOUS TRACK.  AFTER THAT
 TIME...THE GUIDANCE HAS SHIFTED A LITTLE WESTWARD IN RESPONSE TO
 THE GLOBAL MODELS FORECASTING THE WEAKNESS IN THE SUBTROPICAL RIDGE
 TO BE SOMEWHAT FARTHER WEST THAN BEFORE.  THE ECMWF IN PARTICULAR
 HAS MADE A SIGNIFICANT SHIFT...SHOWING A WEST-NORTHWESTWARD MOTION
 INTO THE CENTRAL GULF OF MEXICO BY DAY 5.  DESPITE THE GENERAL
 WESTWARD SHIFT...THE HWRF AND CANADIAN MODELS STILL CALL FOR ISAAC
 TO MOVE UP THE FLORIDA PENINSULA.  THUS... SIGNIFICANT UNCERTAINTY
 REMAINS ABOUT THE THREAT ISAAC POSES TO FLORIDA AND OTHER PORTIONS
 OF THE GULF COAST.  THE 96-120 HR POINTS HAVE BEEN SHIFTED A LITTLE
 WESTWARD FROM THE PREVIOUS ADVISORY AND LIE NEAR THE CENTER OF THE
 GUIDANCE ENVELOPE AND THE CONSENSUS MODELS.
 
 IN THE SHORT TERM...THE STRUCTURE OF ISAAC SUGGESTS THAT ONLY SLOW
 STRENGTHENING IS LIKELY.  HOWEVER...THE ENVIRONMENTAL CONDITIONS
 ARE FAVORABLE FOR RAPID INTENSIFICATION...WHICH COULD OCCUR IF THE
 CYCLONE DEVELOPS A WELL-DEFINED INNER CORE.  WHILE THE OFFICIAL
 FORECAST NO LONGER SHOWS IT...ISAAC COULD REACH HURRICANE INTENSITY
 ABOUT THE TIME IT MAKES LANDFALL IN HISPANIOLA BETWEEN 24-36 HR. 
 AFTER THAT...PASSAGE OVER HISPANIOLA AND CUBA SHOULD CAUSE SOME
 WEAKENING. THE INTENSITY FORECAST SHOWS STRENGTHENING OVER THE GULF
 OF MEXICO...AND THE CURRENT 120 HR INTENSITY COULD BE CONSERVATIVE
 IF THE GLOBAL MODEL UPPER-LEVEL WIND FORECASTS VERIFY.  THE NEW
 INTENSITY FORECAST IS SIMILAR TO THE PREVIOUS FORECAST AND REMAINS
 STRONGER THAN THE INTENSITY CONSENSUS.
 
 THE NOAA G-IV JET AND AN AIR FORCE RESERVE HURRICANE HUNTER AIRCRAFT
 ARE CURRENTLY CONDUCTING A SYNOPTIC SURVEILLANCE MISSION AROUND
 ISAAC.  THE DATA WILL BE AVAILABLE FOR THE 0000 UTC MODEL RUNS.
  
  
 FORECAST POSITIONS AND MAX WINDS
  
 INIT  23/2100Z 16.0N  67.1W   35 KT  40 MPH
  12H  24/0600Z 16.6N  69.0W   40 KT  45 MPH
  24H  24/1800Z 17.5N  71.5W   50 KT  60 MPH
  36H  25/0600Z 18.9N  74.0W   60 KT  70 MPH
  48H  25/1800Z 20.3N  76.2W   55 KT  65 MPH...INLAND
  72H  26/1800Z 23.0N  80.0W   50 KT  60 MPH...OVER WATER
  96H  27/1800Z 25.5N  83.0W   65 KT  75 MPH
 120H  28/1800Z 28.5N  85.5W   75 KT  85 MPH
  
 $$
 FORECASTER BEVEN