099 
 WTNT44 KNHC 251502
 TCDAT4
  
 TROPICAL STORM ISAAC DISCUSSION NUMBER  18
 NWS NATIONAL HURRICANE CENTER MIAMI FL       AL092012
 1100 AM EDT SAT AUG 25 2012
 
 ISAAC HAS BEEN SOMEWHAT DISRUPTED BY ITS PASSAGE ACROSS HAITI.  THE
 LAST REPORT FROM AN AIR FORCE RESERVE HURRICANE HUNTER AIRCRAFT
 SHOWED THAT THE CENTER PRESSURE HAD RISEN TO 998 MB...AND THAT THE
 STRONGEST FLIGHT-LEVEL WINDS WERE 60-70 N MI FROM THE CENTER.  THESE
 WINDS SUPPORT AN INITIAL INTENSITY OF 50 KT.  THE CONVECTIVE
 PATTERN IS DISORGANIZED...WITH LARGE CONVECTIVE BANDS SOUTH OF
 HISPANIOLA AND LITTLE CONVECTION CURRENTLY NEAR THE CENTER.  IT
 SHOULD BE NOTED THAT ISAAC IS AT THE EASTERN END OF A LARGE AND
 ELONGATED LOW PRESSURE SYSTEM OVER THE NORTHWESTERN CARIBBEAN
 SEA...WHICH IS CREATING A LARGE AREA OF STRONG EASTERLY LOW-LEVEL
 WINDS WELL TO THE NORTHWEST OF THE CENTER.
 
 THE LOW-LEVEL CENTER HAS JOGGED WESTWARD DURING THE PAST FEW
 HOURS...AND THE INITIAL MOTION IS A SOMEWHAT UNCERTAIN 315/15.  IN
 THE SHORT-TERM...A MID/UPPER-LEVEL TROUGH OVER THE EASTERN UNITED
 STATES IS LIFTING OUT TO THE NORTHEAST AS A UPPER-LEVEL LOW MOVES
 SOUTHWARD ACROSS THE CENTRAL GULF OF MEXICO.  THIS EVOLUTION...
 COMBINED WITH THE LOW-LEVEL RIDGE NORTH OF ISAAC...SHOULD STEER THE
 CYCLONE GENERALLY NORTHWESTWARD NEAR THE NORTH COAST OF CUBA AND THE
 FLORIDA KEYS DURING THE NEXT 48 HR AS INDICATED BY THE TIGHTLY-
 CLUSTERED MODEL GUIDANCE.  AFTER THAT...THE CYCLONE IS EXPECTED TO
 MOVE AROUND THE WESTERN END OF THE SUBTROPICAL RIDGE AND TURN MORE
 NORTHWARD OVER THE EASTERN GULF OF MEXICO.  WHILE THE GUIDANCE
 GENERALLY AGREES WITH THIS SCENARIO...THERE IS A SPREAD IN
 POTENTIAL LANDFALL LOCATIONS BETWEEN THE EASTERN FLORIDA PANHANDLE
 AND SOUTHEASTERN LOUISIANA...WHICH LOWERS CONFIDENCE IN THE FINAL
 LANDFALL POINT.  THE NEW FORECAST TRACK FOLLOWS THE CENTER OF THE
 GUIDANCE ENVELOPE AND THE CONSENSUS MODELS IN CALLING FOR LANDFALL
 IN THE WESTERN FLORIDA PANHANDLE BETWEEN 72-96 HR.
 
 LITTLE CHANGE IN STRENGTH IS EXPECTED TODAY DUE TO A COMBINATION OF
 LAND INTERACTION...SOME WESTERLY SHEAR...AND THE CURRENT LACK OF
 CONVECTION.  THE SHEAR IS FORECAST TO DECREASE AS THE CENTER MOVES
 AWAY FROM LAND...WOULD SHOULD ALLOW FOR STRENGTHENING AFTER 12 HR. 
 THE NEW INTENSITY FORECAST IS SIMILAR TO THE PREVIOUS FORECAST
 THROUGH 48 HR...THEN CALLS FOR A LITTLE MORE STRENGTHENING THAN THE
 PREVIOUS FORECAST OVER THE NORTHERN GULF.  THE CYCLONE SHOULD
 WEAKEN TO A DEPRESSION AFTER LANDFALL ON THE NORTHERN GULF COAST.
   
 THE NEW NHC FORECAST NECESSITATES THE ISSUANCE OF ADDITIONAL
 TROPICAL STORM WARNINGS AND WATCHES FOR PORTIONS OF THE FLORIDA
 PENINSULA.
  
 IT IS IMPORTANT NOT TO FOCUS ON THE EXACT TRACK OF ISAAC DUE TO THE
 UNCERTAINTIES IN THE FORECAST AND THE FACT THAT ISAAC HAS A LARGE
 AREA OF TROPICAL STORM FORCE WINDS ASSOCIATED WITH IT.
  
 FORECAST POSITIONS AND MAX WINDS
  
 INIT  25/1500Z 20.1N  74.6W   50 KT  60 MPH
  12H  26/0000Z 21.7N  76.4W   50 KT  60 MPH
  24H  26/1200Z 23.3N  79.0W   55 KT  65 MPH
  36H  27/0000Z 24.7N  81.3W   65 KT  75 MPH
  48H  27/1200Z 25.9N  83.1W   75 KT  85 MPH
  72H  28/1200Z 28.5N  85.5W   85 KT 100 MPH
  96H  29/1200Z 31.5N  86.5W   65 KT  75 MPH...INLAND
 120H  30/1200Z 33.0N  86.0W   30 KT  35 MPH...INLAND
  
 $$
 FORECASTER BEVEN