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Tropical Storm KAREN Forecast Discussion Number 9
2013-10-05 10:47:47| National Hurricane Center (Atlantic)
Issued at 400 AM CDT SAT OCT 05 2013 000 WTNT42 KNHC 050847 TCDAT2 TROPICAL STORM KAREN DISCUSSION NUMBER 9 NWS NATIONAL HURRICANE CENTER MIAMI FL AL122013 400 AM CDT SAT OCT 05 2013 KAREN REMAINS A SHEARED CYCLONE THIS MORNING...WITH THE MAIN CONVECTIVE AREA LOCATED ABOUT 80 N MI SOUTHEAST OF THE CENTER. EARLIER ASCAT OVERPASSES INDICATE WINDS OF AT BEST 35 KT IN THE NORTHEASTERN QUADRANT. THERE ARE RECENT REPORTS FROM AN AIR FORCE RESERVE HURRICANE HUNTER AIRCRAFT OF STRONGER WINDS IN THE CONVECTION...BUT IT IS UNCLEAR HOW REPRESENTATIVE THESE WINDS ARE. THE INITIAL INTENSITY IS DECREASED TO 35 KT BASED ON THE SCATTEROMETER DATA. KAREN JOGGED A BIT NORTHWESTWARD DURING THE PAST SEVERAL HOURS...BUT IT APPEARS TO HAVE RESUMED A NORTH-NORTHWESTWARD MOTION OF 330/7. THE LOW/MID-LEVEL RIDGE CURRENTLY STEERING KAREN SHOULD WEAKEN TODAY AS A DEEP-LAYER TROUGH AND ASSOCIATED COLD FRONT MOVE EASTWARD THROUGH THE CENTRAL UNITED STATES. THIS SHOULD CAUSE KAREN TO TURN NORTHWARD AND THEN NORTHEASTWARD DURING THE NEXT COUPLE OF DAYS. WHILE THE TRACK GUIDANCE AGREES WITH THIS SCENARIO...THERE REMAINS SOME SPREAD ON THE TIMING OF THE NORTHEASTWARD TURN. THE NEW TRACK FORECAST IS NUDGED NORTHWARD BASED ON THE INITIAL POSITION AND MOTION...AND IT CALLS FOR THE CENTER TO PASS NEAR OR OVER THE MOUTH OF THE MISSISSIPPI RIVER IN 24-36 HOURS...FOLLOWED BY A FINAL LANDFALL IN ALABAMA OR THE WESTERN FLORIDA PANHANDLE BETWEEN 36-48 HOURS. THE NEW FORECAST TRACK LIES NEAR THE CENTER OF THE GUIDANCE ENVELOPE. THERE ARE SEVERAL POSSIBLE SCENARIOS FOR THE LOW CONFIDENCE INTENSITY FORECAST. THE MOST LIKELY SCENARIO...AND THE ONE USED IN THE NEW INTENSITY FORECAST...IS THAT KAREN REMAINS A SHEARED SYSTEM WITH LITTLE CHANGE IN STRENGTH UNTIL FINAL LANDFALL. ONE ALTERNATIVE IS POSSIBLE STRENGTHENING BEFORE LANDFALL DUE TO RE-DEVELOPED CENTRAL CONVECTION. WHILE THE DYNAMICAL MODELS FORECAST UPPER-LEVEL WINDS THAT COULD ALLOW THIS TO HAPPEN...THEY ARE FOR THE MOST PART SHOWING NO SIGNIFICANT STRENGTHENING AS KAREN APPROACHES LANDFALL. A SECOND ALTERNATIVE IS THAT KAREN WEAKENS BELOW TROPICAL STORM STRENGTH BEFORE LANDFALL DUE TO EITHER LACK OF CONVECTION OR THE START OF EXTRATROPICAL TRANSITION. AFTER LANDFALL...KAREN SHOULD WEAKEN AND BECOME EXTRATROPICAL AS IT MERGES WITH THE COLD FRONT. FORECAST POSITIONS AND MAX WINDS INIT 05/0900Z 27.1N 91.3W 35 KT 40 MPH 12H 05/1800Z 27.6N 91.2W 35 KT 40 MPH 24H 06/0600Z 28.4N 90.5W 35 KT 40 MPH 36H 06/1800Z 29.5N 89.2W 35 KT 40 MPH 48H 07/0600Z 31.2N 86.4W 30 KT 35 MPH...INLAND 72H 08/0600Z 35.5N 80.5W 25 KT 30 MPH...POST-TROP/EXTRATROP 96H 09/0600Z...DISSIPATED $$ FORECASTER BEVEN
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