104 
 WTNT44 KNHC 242055
 TCDAT4
  
 TROPICAL STORM ISAAC DISCUSSION NUMBER  15
 NWS NATIONAL HURRICANE CENTER MIAMI FL       AL092012
 500 PM EDT FRI AUG 24 2012
  
 RECONNAISSANCE AIRCRAFT DATA INDICATE THAT THE CIRCULATION OF ISAAC
 HAS BECOME BETTER ORGANIZED THIS AFTERNOON...WITH A WELL-DEFINED
 AND MORE CIRCULAR INNER CIRCULATION.  THE MAXIMUM 850 MB
 FLIGHT-LEVEL WINDS HAVE BEEN 70 KT...THE MAXIMUM RELIABLE SFMR
 SURFACE WIND ESTIMATE HAS BEEN 55 KT...AND THE MINIMUM REPORTED
 PRESSURE HAS BEEN 994 MB.  BASED ON THESE DATA...THE INITIAL
 INTENSITY IS INCREASED TO 55 KT.  ONE SIGN OF ONGOING ORGANIZATION
 ISSUES...HOWEVER...IS THE LACK OF PERSISTENCE OF THE INNER CORE
 CONVECTION...WHICH HAS WANED OVER THE PAST FEW HOURS.
 
 ISAAC HAS MADE ITS EXPECTED TURN TOWARD THE NORTHWEST AND THE
 INITIAL MOTION IS NOW 315/14.  DURING THE FIRST 48-60 HR...THE
 TRACK GUIDANCE MADE AN EASTWARD SHIFT SINCE THE LAST ADVISORY. 
 THIS WAS LED BY THE GFS...WHICH CHANGED TO A TRACK INTO THE
 SOUTHEASTERN GULF OF MEXICO TO LANDFALL IN SOUTHEASTERN FLORIDA. 
 THE ECMWF AND UKMET ARE NOW ON THE LEFT EDGE OF THE GUIDANCE...
 SHOWING A TRACK ALONG THE NORTH COAST OF CUBA.  THIS PART OF
 THE FORECAST TRACK IS SHIFTED EASTWARD BUT STILL LIES A LITTLE TO
 THE LEFT OF THE CENTER OF THE GUIDANCE ENVELOPE AND THE CONSENSUS
 MODELS.  THERE REMAINS A SPREAD IN THE MODEL GUIDANCE AFTER 48
 HR.  THE GFS-BASED GUIDANCE SHOWS A NORTHEASTWARD MOTION AFTER
 LANDFALL ON THE NORTHERN GULF COAST...WHILE THE UKMET AND ECMWF
 SHOW A NORTHWARD MOTION.  THE LATTER PART OF THE FORECAST TRACK IS
 SHIFTED EASTWARD CLOSE TO THE CONSENSUS MODELS.
  
 THE MAIN CONVECTIVE BAND AND STRONGEST WINDS NORTHEAST OF THE CENTER
 ARE MOVING INLAND AT THIS TIME.  BASED ON THIS AND THE CURRENT LACK
 OF CONVECTION NEAR THE CENTER...LITTLE CHANGE IN STRENGTH IS
 EXPECTED BEFORE LANDFALL.  THE INTENSITY FROM 12-48 HR WILL BE
 DETERMINED BY THE AMOUNT OF LAND INTERACTION.  THE CURRENT FORECAST
 IS BASED ON THE PREMISE THAT ISAAC WILL REMAIN OVER LAND LONG
 ENOUGH TO ALLOW GRADUAL WEAKENING.  HOWEVER...ANY CHANGE IN THE
 TRACK THAT ALLOWS IT TO REMAIN OVER WATER FOR A LONGER TIME COULD
 ALLOW IT TO BE STRONGER THAN FORECAST.  AFTER 48 HR...THE
 ENVIRONMENTAL CONDITIONS APPEAR GENERALLY FAVORABLE FOR ISAAC TO
 STRENGTHEN INTO A HURRICANE OVER THE GULF OF MEXICO...AND THE
 INTENSITY FORECAST REFLECTS THIS.  CONVERSELY...A LONGER TRACK OVER
 LAND MAY DISRUPT ISAAC ENOUGH TO BE UNABLE TO TAKE ADVANTAGE OF
 THESE FAVORABLE CONDITIONS.
  
 IT IS IMPORTANT NOT TO FOCUS ON THE EXACT TRACK DUE TO THE
 UNCERTAINTIES IN THE FORECAST AND THE FACT THAT ISAAC HAS A LARGE
 AREA OF TROPICAL STORM FORCE WINDS ASSOCIATED WITH IT.  THE TROPICAL
 STORM WATCH FOR SOUTH FLORIDA AND THE FLORIDA KEYS MAY HAVE TO BE
 UPGRADED TO A HURRICANE WATCH IF THE INTENSITY FORECAST IS REVISED
 UPWARD.
  
 FORECAST POSITIONS AND MAX WINDS
  
 INIT  24/2100Z 17.2N  71.9W   55 KT  65 MPH
  12H  25/0600Z 18.7N  73.6W   50 KT  60 MPH
  24H  25/1800Z 20.7N  76.2W   50 KT  60 MPH...INLAND
  36H  26/0600Z 22.4N  78.6W   45 KT  50 MPH...NEAR COAST OF CUBA
  48H  26/1800Z 23.9N  80.7W   55 KT  65 MPH...OVER WATER
  72H  27/1800Z 26.5N  84.0W   65 KT  75 MPH
  96H  28/1800Z 29.5N  86.0W   75 KT  85 MPH
 120H  29/1800Z 32.0N  86.0W   45 KT  50 MPH...INLAND
  
 $$
 FORECASTER BEVEN