449 
 WTNT44 KNHC 281459
 TCDAT4
  
 TROPICAL STORM ISAAC DISCUSSION NUMBER  30
 NWS NATIONAL HURRICANE CENTER MIAMI FL       AL092012
 1000 AM CDT TUE AUG 28 2012
  
 REPORTS FROM AIR FORCE AND NOAA HURRICANE HUNTER AIRCRAFT INDICATE
 THE CENTRAL PRESSURE HAS DECREASED TO ABOUT 976 MB SINCE THE
 PREVIOUS ADVISORY...BUT IT HAS LEVELED OFF OVER THE PAST FEW HOURS.
 THE MAXIMUM 850 MB FLIGHT-LEVEL WIND OBSERVED HAS BEEN 89 KT...
 WHICH EQUATES TO A SURFACE WIND OF ABOUT 71 KT. HOWEVER...
 BIAS-ADJUSTED SFMR SURFACE WINDS HAVE ONLY BEEN AROUND 60-62 KT...
 WHICH CORRELATES WELL WITH DROPSONDE BOUNDARY LAYER-DERIVED SURFACE
 WINDS. AS SUCH...THE INTENSITY OF ISAAC IS BEING MAINTAINED AT 60
 KT...WHICH IS JUST BELOW HURRICANE STATUS.
 
 CENTER FIXES FROM THE AIRCRAFT INDICATE THAT ISAAC HAS BEEN WOBBLING
 IN A GENERAL NORTHWESTWARD MOTION OF 310/09 KT. THERE REMAINS NO
 SIGNIFICANT CHANGE TO THE PREVIOUS FORECAST TRACK OR REASONING.    
 ISAAC IS FORECAST TO MOVE INTO A WEAKNESS IN THE SUBTROPICAL RIDGE
 NEAR THE NORTH-CENTRAL GULF COAST OVER THE NEXT 24-36 HOURS...
 ACCOMPANIED BY A GRADUAL DECREASE IN THE FORWARD SPEED. AS THE 
 RIDGE BUILDS BACK IN TO THE NORTH OF THE CYCLONE...ISAAC IS
 EXPECTED TO TURN A LITTLE MORE TOWARD THE WEST-NORTHWEST BEFORE IT
 TURNS NORTHWARD ON DAY 4...AND MOVES NORTHEASTWARD INTO THE OHIO
 VALLEY REGION ON DAY 5. THE OFFICIAL FORECAST TRACK HAS BEEN NUDGED
 A LITTLE TO THE LEFT OF THE PREVIOUS ADVISORY TRACK AND LIES JUST
 TO THE RIGHT OF THE CONSENSUS MODELS TV15 AND TCVA.
 
 MID-LEVEL DRY AIR ENTRAINMENT CONTINUES TO PLAGUE ISAAC. AS SOON AS
 THE CYCLONE DEVELOPS INNER-CORE CONVECTION AND THE APPEARANCE OF AN
 EYE IN RADAR AND SATELLITE IMAGERY...THE CONVECTION ERODES DUE TO
 THE DRY AIR. DESPITE THE FAVORABLE OCEANIC CONDITIONS AND
 UPPER-LEVEL OUTFLOW REGIME...ISAAC ONLY HAS ABOUT 12-18 HOURS FOR
 FURTHER STRENGTHENING TO OCCUR. THE OFFICIAL INTENSITY FORECAST IS
 SIMILAR TO THE PREVIOUS ADVISORY...WITH ONLY TIMING ADJUSTMENTS
 MADE TO THE INTENSITY FORECAST...AND CLOSELY FOLLOWS THE INTENSITY
 MODEL CONSENSUS.
  
 ISAAC IS A LARGE TROPICAL CYCLONE.  A DANGEROUS STORM SURGE...HEAVY
 RAINFALL...AND STRONG WINDS EXTEND WELL AWAY FROM THE CENTER AND
 ARE EXPECTED TO AFFECT A LARGE PORTION OF THE NORTHERN GULF COAST.
 FOR THIS REASON...IT IS IMPORTANT NOT TO FOCUS ON THE EXACT CENTER
 LOCATION.  THE THREAT OF HEAVY RAINFALL AND FLOODING IS ALSO
 EXPECTED TO SPREAD INLAND OVER THE LOWER MISSISSIPPI VALLEY REGION
 DURING THE NEXT FEW DAYS.
  
 FORECAST POSITIONS AND MAX WINDS
  
 INIT  28/1500Z 28.1N  88.5W   60 KT  70 MPH
  12H  29/0000Z 28.8N  89.4W   70 KT  80 MPH
  24H  29/1200Z 29.7N  90.4W   65 KT  75 MPH...INLAND
  36H  30/0000Z 30.5N  91.5W   45 KT  50 MPH...INLAND
  48H  30/1200Z 32.0N  92.0W   35 KT  40 MPH...INLAND
  72H  31/1200Z 35.0N  92.5W   20 KT  25 MPH...INLAND
  96H  01/1200Z 38.5N  90.5W   15 KT  15 MPH...POST-TROP/REMNT LOW
 120H  02/1200Z 41.0N  86.0W   15 KT  15 MPH...POST-TROP/REMNT LOW
  
 $$
 FORECASTER STEWART