501 
 WTNT42 KNHC 042040
 TCDAT2
  
 TROPICAL STORM KAREN DISCUSSION NUMBER   7
 NWS NATIONAL HURRICANE CENTER MIAMI FL       AL122013
 400 PM CDT FRI OCT 04 2013
  
 AFTER A BURST OF DEEP CONVECTION NEAR AND EAST OF THE CENTER EARLIER
 THIS AFTERNOON...THE LOW-LEVEL CENTER OF KAREN IS AGAIN EXPOSED
 WEST OF THE WARMING CLOUD TOPS. DATA FROM AN AIR FORCE RESERVE
 HURRICANE HUNTER AIRCRAFT INDICATE THAT THE INTENSITY OF KAREN
 REMAINS 45 KT...AND A CENTER DROP FROM THE PLANE REPORTED A PRESSURE
 OF 1003 MB. MODERATE SHEAR AND DRY AIR SHOULD RESULT IN LITTLE
 OVERALL INTENSITY CHANGE DURING THE NEXT 24 HOURS...EVEN THOUGH
 SHORT TERM CHANGES IN CONVECTIVE ORGANIZATION COULD RESULT IN SOME
 SHORT TERM FLUCTUATIONS IN INTENSITY. THE GLOBAL MODELS ARE NOW IN
 BETTER AGREEMENT ON THIS EVOLUTION...AND SHOW THE MID-LEVEL
 CIRCULATION WEAKENING OR DISSIPATING ENTIRELY IN THE NEXT DAY OR
 TWO. IN PARTICULAR THE GFS IS WEAKER WITH ITS FORECAST OF KAREN
 AFTER DATA FROM THE NOAA GULFSTREAM-IV JET...WHICH SHOWED 200-MB
 WINDS WEST OF KAREN STRONGER THAN PREVIOUSLY ANALYZED...WERE
 INCORPORATED INTO THE 12Z ANALYSIS. AFTER 24 HOURS...KAREN COULD
 STRENGTHEN A LITTLE DUE TO AN INCREASE IN UPPER-LEVEL DIVERGENCE
 AHEAD OF A MID-LATITUDE TROUGH...BUT SIGNIFICANT STRENGTHENING IS
 NOT EXPECTED. AN ALTERNATIVE SCENARIO IS THAT KAREN COULD BECOME
 COMPLETELY DECOUPLED FROM THE DEEP CONVECTION AND WEAKEN.
  
 THE INITIAL MOTION OF KAREN HAS VARIED DEPENDING ON HOW CLOSE THE
 CONVECTION WAS TO THE CENTER. AFTER MOVING MORE NORTHWARD EARLIER
 THE AFTERNOON THE CENTER HAS WOBBLED WESTWARD AS IT BECAME EXPOSED.
 SMOOTHING THROUGH THESE SHORT TERM VARIATIONS...THE INITIAL MOTION
 ESTIMATE IS 335/06. THE GLOBAL MODELS ARE NOW IN A LITTLE BETTER
 AGREEMENT ON THE HEADING OF THE STORM OVER THE NEXT COUPLE OF
 DAYS...IN PARTICULAR THE GFS HAS SHIFTED TO THE LEFT AND IS NOW
 CLOSER TO THE ECMWF. HOWEVER...THERE REMAIN LARGE DIFFERENCES IN
 FORWARD SPEED WITH THE GUIDANCE CONTINUING TO TREND SLOWER OVERALL.
 THE NHC FORECAST SHOWS A TURN TOWARD THE NORTH BY 24 HOURS AND THEN
 A SHARP NORTHEASTWARD TURN BY 36 HOURS AS KAREN FEELS THE INFLUENCE
 OF THE AFOREMENTIONED TROUGH. THE NHC TRACK HAS BEEN ADJUSTED
 TOWARD THE SLOWER MULTI-MODEL CONSENSUS...BUT IS FASTER AND TO THE
 LEFT OF THE ECMWF AND GFS AFTER 24 HOURS. CONFIDENCE IN THE DETAILS
 OF THE TRACK FORECAST...AND THEREFORE THE DISTRIBUTION OF IMPACTS
 ALONG THE COAST...REMAINS LOW.
  
 GIVEN THE NEW INTENSITY FORECAST...THE HURRICANE WATCH HAS BEEN
 CHANGED TO A TROPICAL STORM WATCH FROM THE MOUTH OF THE PEARL RIVER
 TO DESTIN FLORIDA...AND DISCONTINUED ELSEWHERE.
 
 THE 12Z HWRF RUN SHOWED CONSIDERABLY LESS INTENSIFICATION WITH KAREN
 COMPARED TO PREVIOUS RUNS AFTER ASSIMILATING DATA FROM THE FROM THE
 NOAA P-3 TAIL DOPPLER RADAR. THIS MARKS THE FIRST TIME DOPPLER
 RADAR DATA HAVE BEEN ASSIMILATIED INTO AN OPERATIONAL HURRICANE
 MODEL IN REAL TIME. 
 
 FORECAST POSITIONS AND MAX WINDS
  
 INIT  04/2100Z 25.9N  90.3W   45 KT  50 MPH
  12H  05/0600Z 26.9N  90.6W   45 KT  50 MPH
  24H  05/1800Z 27.9N  90.7W   45 KT  50 MPH
  36H  06/0600Z 28.8N  89.6W   50 KT  60 MPH
  48H  06/1800Z 29.9N  87.7W   50 KT  60 MPH
  72H  07/1800Z 33.0N  82.5W   25 KT  30 MPH...POST-TROP/EXTRATROP
  96H  08/1800Z...ABSORBED
  
 $$
 FORECASTER BRENNAN