933 
 WTNT44 KNHC 220851
 TCDAT4
  
 TROPICAL STORM ISAAC DISCUSSION NUMBER   5
 NWS NATIONAL HURRICANE CENTER MIAMI FL       AL092012
 500 AM AST WED AUG 22 2012
  
 SATELLITE IMAGERY INDICATES A LARGE CENTRAL DENSE OVERCAST FEATURE
 HAS DEVELOPED OVER THE LOW-LEVEL CENTER...WHICH INCLUDES SOME COLD
 CLOUD TOPS OF -82 TO -86C VERY NEAR THE CENTER. HOWEVER...THE SHARP 
 INCREASE IN INNER-CORE CONVECTION HAS NOT YET TRANSLATED INTO ANY
 SIGNIFICANT INTENSIFICATION. AN AIR FORCE RESERVE RECONNAISSANCE
 AIRCRAFT INVESTIGATING ISAAC THIS MORNING HAS ONLY FOUND THE
 CENTRAL PRESSURE TO BE 1003 MB AND 850 MB FLIGHT-LEVEL WINDS OF 47
 KT...WHICH EQUATES TO ABOUT A 40-KT INTENSITY ESTIMATE. SFMR WINDS
 IN VERY HEAVY RAIN HAVE BEEN AS HIGH AS 61 KT. THE BIAS-ADJUSTED
 SFMR WINDS HAVE BEEN RUNNING AS HIGH AS 54 KT...BUT EVEN THOSE
 VALUES APPEAR TO BE INFLATED. UNTIL THE AIRCRAFT COMPLETES ITS
 MISSION... THE INITIAL INTENSITY WILL REMAIN AT 40 KT BASED ON THE
 1003 MB PRESSURE-WIND RELATIONSHIP.
  
 THE INITIAL MOTION ESTIMATE IS 270/15 KT. THE INITIAL POSITION IS A
 BLEND OF THE RECON FIXES AND SATELLITE POSITIONS...AND CONTINUITY
 WITH PREVIOUS FORECAST TRACK. THERE IS NO SIGNIFICANT CHANGE TO THE
 PREVIOUS FORECAST TRACK OR REASONING. THE EAST-WEST ORIENTED
 SUBTROPICAL RIDGE TO THE NORTH OF ISAAC ALONG 30N LATITUDE IS
 FORECAST BY ALL OF THE GLOBAL MODELS TO REMAIN INTACT ACROSS
 FLORIDA AND THE SOUTHEASTERN U.S. THROUGH 72 HOURS OR SO. AFTER
 THAT...A BROAD MID- TO UPPER-LEVEL TROUGH CURRENTLY LOCATED OVER
 THE CENTRAL U.S. FROM THE GREAT LAKES SOUTHWARD TO THE CENTRAL GULF
 COAST IS EXPECTED TO DIG SOUTHWARD OVER THE NEXT 24 HOURS BEFORE
 MOVING EASTWARD. THIS SHOULD RESULT IN AN EROSION OF THE RIDGE
 ACROSS THE EASTERN GULF OF MEXICO AND THE SOUTHEASTERN U.S.
 INCLUDING FLORIDA AND THE NORTHWESTERN BAHAMAS. THIS DEVELOPING
 WEAKNESS IN THE RIDGE SHOULD ALLOW ISAAC TO TURN NORTHWESTWARD
 ACROSS EASTERN AND CENTRAL CUBA BY DAYS 4 AND 5. THE NHC MODEL
 GUIDANCE IS IN EXCELLENT AGREEMENT ON THIS EVOLVING SCENARIO WITH
 THE ECMWF BEING THE LEFTMOST OF THE MODELS...AND THE GFDL AND HWRF
 BEING THE RIGHTMOST OF THE MODELS. GIVEN THE RUN-TO-RUN CONSISTENCY
 OF THE GFS AND UKMET MODELS...MORE WEIGHT HAS BEEN PLACED ON THOSE
 SOLUTIONS...ESPECIALLY SINCE THEY HAVE A STRONGER AND VERTICALLY
 DEEPER CYCLONE DEPICTED IN THE MODELS.
 
 SHEAR ANALYSES FROM THE GFS-BASED SHIPS INTENSITY MODEL AND UW-CIMSS
 INDICATE BOTH THE DEEP-LAYER AND MID-LEVEL SHEAR VALUES HAVE
 DROPPED BELOW 10 KT...WHICH HAS FINALLY ALLOWED DEEP CONVECTION TO
 DEVELOP AND PERSIST OVER THE LOW-LEVEL CENTER. THE SHEAR IS
 FORECAST TO GRADUALLY DECREASE TO VALUES BELOW 5 KT BY 24 HOURS...
 WHICH SHOULD ALLOW ISAAC TO STRENGTHEN TO A HURRICANE BY 48 HOURS.
 AT 72 AND 96 HOURS...THE INTENSITY HAS BEEN DECREASED DUE TO
 EXPECTED LAND INTERACTION WITH HAITI AND EASTERN CUBA. AFTER 96
 HOURS...HOWEVER...ISAAC SHOULD BE MOVING BACK OVER THE VERY WARM
 WATER BETWEEN CUBA AND FLORIDA. WITH SEA-SURFACE TEMPERATURES
 EXPECTED TO BE NEAR 30C AND THE GFS AND UKMET MODELS DEPICTING A
 EXTENSIVE UPPER-LEVEL OUTFLOW REGIME COMPLETE WITH DUAL OUTFLOW
 CHANNELS TO THE NORTHWEST AND SOUTHEAST...STRENGTHENING APPEARS
 LIKELY. THE OFFICIAL INTENSITY REMAINS ON THE CONSERVATIVE SIDE DUE
 TO UNCERTAINTY IN HOW LONG AND HOW MUCH ISAAC WILL INTERACT WITH
 HISPANIOLA AND CUBA...AND IS CLOSE TO A BLEND OF THE SHIPS...
 DECAY-SHIPS...AND LGEM STATISTICAL-DYNAMICAL INTENSITY MODELS.
 
 FORECAST POSITIONS AND MAX WINDS
  
 INIT  22/0900Z 15.5N  57.3W   40 KT  45 MPH
  12H  22/1800Z 15.9N  59.7W   45 KT  50 MPH
  24H  23/0600Z 16.3N  62.8W   55 KT  65 MPH
  36H  23/1800Z 16.8N  65.7W   65 KT  75 MPH
  48H  24/0600Z 17.3N  68.4W   75 KT  85 MPH
  72H  25/0600Z 18.8N  73.2W   65 KT  75 MPH...OVER WATER
  96H  26/0600Z 21.8N  77.1W   65 KT  75 MPH...OVER WATER
 120H  27/0600Z 24.8N  80.0W   80 KT  90 MPH
  
 $$
 FORECASTER STEWART