941 
 WTNT45 KNHC 160245
 TCDAT5
  
 TROPICAL STORM ERIN DISCUSSION NUMBER   5
 NWS NATIONAL HURRICANE CENTER MIAMI FL       AL052013
 1100 PM AST THU AUG 15 2013
 
 CONVECTION ASSOCIATED WITH ERIN HAS BEEN ON THE WANE DURING MOST OF
 THE EVENING HOURS...ALTHOUGH RECENTLY A SMALL BURST HAS FORMED EAST
 OF THE CENTER.  MICROWAVE PASSES SUGGEST THE SYSTEM IS NOT WELL
 ORGANIZED...WITH THE LOW-LEVEL CENTER APPARENTLY WEST OF THE MID-
 LEVEL CENTER.  THE INITIAL INTENSITY IS BEING HELD AT 35 KT IN
 AGREEMENT WITH THE DVORAK ESTIMATE FROM TAFB.  THE OVERALL
 ENVIRONMENT FOR THE NEXT DAY OR TWO SEEMS TO BE CONDUCIVE FOR SOME
 STRENGTHENING WITH THE SHEAR FORECAST TO BE LIGHT BUT A LIMITING
 FACTOR OF MARGINAL SSTS. IN A FEW DAYS...ALTHOUGH SSTS ARE FORECAST
 TO INCREASE...THE GLOBAL MODELS SHOW AN INCREASE IN SHEAR...WHICH
 WOULD FACILITATE RATHER DRY AIR ALOFT ENTRAINING INTO THE CENTRAL
 CORE OF ERIN.  THUS...THE OFFICIAL NHC FORECAST SHOWS WEAKENING
 AFTER DAY 3...WHICH IS CONSISTENT WITH THE PREVIOUS FORECAST AND
 THE FLORIDA STATE SUPERENSEMBLE.  
 
 MICROWAVE FIXES GIVE AN INITIAL MOTION OF 295/13. THIS GENERAL
 COURSE IS EXPECTED FOR THE NEXT COUPLE OF DAYS WHILE A MID-LEVEL
 RIDGE REMAINS TO THE NORTHEAST OF THE TROPICAL CYCLONE. AFTER THAT
 TIME...THE BIGGEST UNCERTAINTY IS WHETHER A WEAKNESS IN THE RIDGE
 FROM A MID- TO UPPER-LEVEL LOW LOCATED OVER THE EASTERN ATLANTIC 
 WILL ALLOW THAT TRACK TO CONTINUE.  IF THE STORM IS SHALLOW
 ENOUGH...IT WILL PROBABLY MISS THE WEAKNESS AND INSTEAD TAKE A MORE
 WESTWARD TURN BECAUSE OF A STRONGER LOW-LEVEL RIDGE. ALTHOUGH THE
 NEW NHC FORECAST IS SHIFTED NORTHWARD TO COME INTO BETTER AGREEMENT
 WITH THE SOUTHERN SIDE OF THE GUIDANCE ENVELOPE...IT IS STILL WELL
 TO THE SOUTH OF THE DYNAMICAL MODEL CONSENSUS. FURTHER ADJUSTMENTS
 COULD STILL BE NECESSARY IF THIS NORTHWARD TREND IN THE GUIDANCE
 PERSISTS IN FUTURE CYCLES.
  
  
 FORECAST POSITIONS AND MAX WINDS
  
 INIT  16/0300Z 15.5N  29.1W   35 KT  40 MPH
  12H  16/1200Z 16.3N  31.1W   35 KT  40 MPH
  24H  17/0000Z 17.5N  33.4W   40 KT  45 MPH
  36H  17/1200Z 18.6N  35.5W   45 KT  50 MPH
  48H  18/0000Z 19.6N  37.4W   45 KT  50 MPH
  72H  19/0000Z 20.5N  41.5W   45 KT  50 MPH
  96H  20/0000Z 21.5N  46.0W   35 KT  40 MPH
 120H  21/0000Z 22.5N  50.0W   30 KT  35 MPH
  
 $$
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