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Tropical Storm KAREN Forecast Discussion Number 3
2013-10-03 22:50:42| National Hurricane Center (Atlantic)
Issued at 400 PM CDT THU OCT 03 2013 000 WTNT42 KNHC 032050 TCDAT2 TROPICAL STORM KAREN DISCUSSION NUMBER 3 NWS NATIONAL HURRICANE CENTER MIAMI FL AL122013 400 PM CDT THU OCT 03 2013 THE SATELLITE APPEARANCE OF KAREN REMAINS LESS THAN IMPRESSIVE...AS THE CENTER HAS BEEN PARTIALLY EXPOSED TO THE WEST OF THE REMAINING DEEP CONVECTION. THE SHIPS MODEL CONTINUES TO ANALYZE ABOUT 20 KT OF SOUTHWESTERLY SHEAR OVER KAREN...AND DRY AIR IS PRESENT IN THE MID/UPPER LEVELS OVER THE WESTERN SEMICIRCLE. DESPITE THESE NEGATIVE FACTORS...KAREN CONTINUES TO MAINTAIN ITS INTENSITY. THE NOAA HURRICANE HUNTERS JUST MEASURED A CENTRAL PRESSURE OF 999 MB...AND FLIGHT-LEVEL AND SFMR WINDS FROM BOTH THE NOAA AND AIR FORCE RESERVE AIRCRAFT SUPPORT MAINTAINING THE INITIAL INTENSITY AT 55 KT. MODERATE SHEAR IS EXPECTED TO CONTINUE...AND ONLY GRADUAL STRENGTHENING IS EXPECTED BEFORE THE SHEAR INCREASES FURTHER IN ABOUT 48 HOURS. SOME WEAKENING IS THEN ANTICIPATED AS KAREN APPROACHES THE GULF COAST...BUT THE STORM COULD STILL BE NEAR HURRICANE STRENGTH AT LANDFALL. THE NHC FORECAST IS CLOSE TO THE SHIPS AND LGEM MODELS AND THE IVCN INTENSITY CONSENSUS THROUGH THE PERIOD. KAREN SHOULD BE EXTRATROPICAL BY ABOUT 4 DAYS AND ABSORBED BY DAY 5...IF NOT SOONER. THE INITIAL MOTION ESTIMATE IS A MORE CONFIDENT 330/10 BASED ON AIRCRAFT FIXES AND SATELLITE IMAGERY. THE TRACK FORECAST REASONING REMAINS UNCHANGED...AS KAREN WILL MOVE AROUND THE PERIPHERY OF THE SUBTROPICAL RIDGE DURING THE NEXT DAY OR SO...WITH A DECREASE IN FORWARD SPEED AS A MID-LEVEL RIDGE BUILDS BRIEFLY TO THE NORTHEAST OF THE CYCLONE. A NORTHEASTWARD ACCELERATION IS EXPECTED AFTER 48 HOURS AHEAD OF A MID/UPPER-LEVEL TROUGH. THE TRACK GUIDANCE HAS AGAIN SHIFTED A LITTLE TO THE WEST THIS CYCLE...AND THERE REMAINS CONSIDERABLE EAST/WEST SPREAD...WITH THE HWRF AND GFS TO THE EAST AND THE ECMWF TO THE WEST. THE NHC TRACK HAS BEEN ADJUSTED TO THE WEST ABOUT A HALF A DEGREE BUT STILL LIES A LITTLE TO THE EAST OF THE LATEST TCVA CONSENSUS...AND IS CLOSE TO THE FSU SUPERENSEMBLE THROUGH LANDFALL. THE 34-KT WIND RADII HAVE BEEN ADJUSTED OUTWARD IN THE EASTERN SEMICIRCLE BASED ON AN EARLIER ASCAT PASS. GIVEN THE NEW NHC TRACK AND INTENSITY FORECAST...A TROPICAL STORM WARNING HAS BEEN ISSUED FOR A PORTION OF SOUTHEASTERN LOUISIANA. FORECAST POSITIONS AND MAX WINDS INIT 03/2100Z 23.3N 88.5W 55 KT 65 MPH 12H 04/0600Z 24.6N 89.3W 60 KT 70 MPH 24H 04/1800Z 26.2N 89.9W 60 KT 70 MPH 36H 05/0600Z 27.6N 89.8W 65 KT 75 MPH 48H 05/1800Z 28.8N 89.3W 60 KT 70 MPH 72H 06/1800Z 32.0N 86.0W 40 KT 45 MPH...INLAND 96H 07/1800Z 36.0N 80.5W 25 KT 30 MPH...POST-TROP/EXTRATROP 120H 08/1800Z...ABSORBED BY FRONT $$ FORECASTER BRENNAN
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