314 
 WTNT44 KNHC 260244
 TCDAT4
  
 TROPICAL STORM ISAAC DISCUSSION NUMBER  20
 NWS NATIONAL HURRICANE CENTER MIAMI FL       AL092012
 1100 PM EDT SAT AUG 25 2012
  
 SATELLITE AND RADAR DATA FROM CUBA SHOW THAT ISAAC IS MOVING
 PARALLEL TO...BUT OFFSHORE OF...THE NORTHERN COAST OF CUBA.
 THE HURRICANE HUNTER AIRCRAFT DID NOT FIND ANY STRONGER WINDS
 DURING THE LATTER PORTION OF THE FLIGHT AND THE INITIAL WIND
 SPEED REMAINS 50 KT.  HOWEVER...THUNDERSTORM ACTIVITY HAS
 INCREASED IN A BAND TO THE NORTH AND EAST OF THE CENTER DURING
 THE PAST FEW HOURS AND ISAAC MAY BE ON THE VERGE OF STRENGTHENING.
 THE NEXT RECONNAISSANCE FLIGHT IS EXPECTED TO BE IN THE CYCLONE
 AROUND 0600 UTC.
  
 THE INITIAL MOTION ESTIMATE IS 305/15 KT.  ISAAC SHOULD CONTINUE ON
 A WEST-NORTHWESTWARD TO NORTHWESTWARD MOTION DURING THE NEXT 24
 HOURS OR SO BETWEEN A LARGE LOW/MID-LEVEL LOW PRESSURE SYSTEM OVER
 THE NORTHWESTERN CARIBBEAN SEA AND A MID-LEVEL RIDGE OVER THE
 WESTERN ATLANTIC.  THE MODEL GUIDANCE IS TIGHTLY CLUSTERED DURING
 THIS TIME AND SHOWS A TRACK OVER THE STRAITS OF FLORIDA AND NEAR OR
 OVER THE FLORIDA KEYS.  IN ABOUT 48 HOURS...ISAAC WILL BE NEARING
 THE WESTERN PORTION OF THE RIDGE AND SHOULD MOVE IN A GENERAL
 NORTHWESTWARD HEADING OVER THE EASTERN GULF OF MEXICO...BUT LARGE
 DIFFERENCES EXIST BETWEEN THE LATEST ECMWF AND GFS MODELS AFTER
 THAT TIME.  THE ECMWF RECURVES ISAAC AHEAD OF A MID-LATITUDE
 TROUGH OVER THE EASTERN UNITED STATES...WHILE THE GFS SLOWS ISAAC
 DOWN AS THE TROUGH BYPASSES THE SYSTEM AND THE MODEL THEN TURNS
 THE CYCLONE WESTWARD TO THE SOUTH OF A DEVELOPING MID- TO
 UPPER-LEVEL RIDGE.  THIS BIFURCATION IS ALSO SEEN IN THE MOST RECENT
 ECMWF AND GFS ENSEMBLES WITH ABOUT AN EQUAL NUMBER OF MEMBERS
 SHOWING RECURVATURE VERSUS A CONTINUE NORTHWESTERLY TRACK TOWARD
 THE NORTHERN GULF COAST.  SINCE THE UNCERTAINTY IS LARGE AND EITHER
 OF THESE SCENARIOS ARE POSSIBLE AT THIS TIME...THE NHC FORECAST IS
 LIES BETWEEN THEM.  THE UPDATED TRACK IS VERY CLOSE TO THE PREVIOUS
 ADVISORY THROUGH 36 HOURS.  AFTER THAT TIME...THE TRACK HAS BEEN
 ADJUSTED WESTWARD...BUT IT REMAINS EAST OF THE DYNAMICAL MODEL
 CONSENSUS TO RETAIN SOME CONTINUITY WITH THE PREVIOUS FORECAST.
 
 THE UPPER-LEVEL ENVIRONMENT IS EXPECTED TO BECOME MORE CONDUCIVE FOR
 STRENGTHENING DURING THE NEXT COUPLE OF DAYS AS ISAAC MOVES OVER
 THE WARM WATERS OF THE FLORIDA STRAITS AND EASTERN GULF.  STEADY
 STRENGTHENING IS EXPECTED AND ISAAC IS EXPECTED TO BE AT OR NEAR
 HURRICANE STRENGTH WHEN THE CENTER REACHES THE FLORIDA KEYS.
 ADDITIONAL STRENGTHENING IS LIKELY WHILE THE CYCLONE MOVES OVER THE
 EASTERN GULF OF MEXICO.  THE NEW INTENSITY FORECAST IS A LITTLE
 HIGHER THAN THE PREVIOUS ADVISORY AND IS BETWEEN THE SHIPS/LGEM
 GUIDANCE AND THE MORE AGGRESSIVE HWRF MODEL.
  
 IT IS IMPORTANT NOT TO FOCUS ON THE EXACT FORECAST TRACK SINCE
 SIGNIFICANT HAZARDS EXTEND WELL AWAY FROM THE CENTER.  SINCE LARGE
 UNCERTAINTIES REMAIN IN THE EXTENDED PORTION OF THE FORECAST...IT
 IS TOO EARLY TO DETERMINE EXACTLY WHERE AND WHEN ISAAC WILL MAKE
 LANDFALL ALONG THE GULF COAST.
  
 FORECAST POSITIONS AND MAX WINDS
  
 INIT  26/0300Z 22.1N  77.2W   50 KT  60 MPH
  12H  26/1200Z 23.4N  79.4W   55 KT  65 MPH
  24H  27/0000Z 24.6N  81.8W   65 KT  75 MPH...NEAR FLORIDA KEYS
  36H  27/1200Z 25.8N  83.7W   75 KT  85 MPH
  48H  28/0000Z 27.2N  85.2W   85 KT 100 MPH
  72H  29/0000Z 29.5N  86.5W   90 KT 105 MPH
  96H  30/0000Z 31.5N  86.5W   50 KT  60 MPH...INLAND
 120H  31/0000Z 34.0N  86.0W   25 KT  30 MPH...INLAND
  
 $$
 FORECASTER BROWN