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Tropical Storm KAREN (Text)

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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
 
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FORECASTER BRENNAN
 
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