|
Show Selection: |
| #152943 (Received by flhurricane at: 10:34 PM 28.Sep.2007) TCDAT2 TROPICAL STORM KAREN DISCUSSION NUMBER 17 NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL AL122007 1100 PM EDT FRI SEP 28 2007 DETERMINING THE ACTUAL CENTER OF KAREN HAS BEEN A SIGNIFICANT CHALLENGE THIS EVENING. IT APPEARS THAT THE EARLIER EXPOSED CENTER...NOW MOVING NORTHWESTWARD...HAS BECOME JUST ANOTHER SWIRL AROUND AN ELONGATED LOW-LEVEL CIRCULATION FARTHER TO THE SOUTHWEST. A RECENT QUIKSCAT PASS SUPPORTS THIS ASSESSMENT...SHOWING A LARGE AREA OF LIGHT WINDS SOUTHWEST OF THE OLD CENTER. THUS...THE CENTER IS RELOCATED WESTWARD TO THE LIGHTER WIND AREA AS SUGGESTED BY QUIKSCAT AND NIGHT VISIBLE SATELLITE IMAGES. OVERALL..THE SYSTEM REMAINS VERY DISORGANIZED DUE TO FEROCIOUS WESTERLY SHEAR...WITH THUNDERSTORMS MOSTLY IN THE EASTERN SEMICIRCLE. EVEN WITH THE DISHEVELED SATELLITE APPEARANCE...QUIKSCAT SUPPORTS AN INTENSITY OF AT LEAST 35 KT...AND THE INITIAL INTENSITY WILL BE HELD AT 35 KT. STRONG WESTERLY OR SOUTHWESTERLY SHEAR IS FORECAST TO CONTINUE FOR ABOUT THE NEXT 48 HOURS AND SHOULD INDUCE WEAKENING OF KAREN. THE INTENSITY FORECAST FOR THIS TIME SHOWS THE SYSTEM BARELY HANGING ON AS A TROPICAL CYCLONE....AND DISSIPATION IS POSSIBLE. THEREAFTER...THE GFS AND UKMET MODELS CARVE OUT A PIECE OF THE MID-OCEANIC TROUGH INTO A CUT-OFF LOW THAT MOVES SOUTHWARD NEAR AND THEN TO THE SOUTH OF WHATEVER REMAINS OF KAREN. THIS EVOLUTION COULD PLACE THE SYSTEM IN A MORE FAVORABLE LOCATION FOR SOME STRENGTHENING WITH MORE EASTERLY FLOW ALOFT TO THE NORTH OF THE CUT-OFF LOW. THE GFDL RESPONDS TO THESE CONDITIONS BY MAKING KAREN A HURRICANE IN ABOUT 4 DAYS. HOWEVER...OTHER MODELS KEEP MODERATE TO STRONG SHEAR OVER THE SYSTEM FOR A LONGER PERIOD OF TIME AND THIS SOLUTION WOULD FAVOR DISSIPATION. UNTIL THERE IS SOME CLARITY ON IF THE SYSTEM WILL SURVIVE THE SHEAR...I'M INCLINED TO MAKE LITTLE CHANGE TO THE LONG-TERM FORECAST AND KEEP THE CYCLONE AS A TROPICAL DEPRESSION. OBVIOUSLY...FORECAST CONFIDENCE IS EXTREMELY LOW TONIGHT. TO SMOOTH OUT THE IRREGULAR MOTION DURING THE PAST 24 HOURS... A LONG-TERM MOVEMENT WILL BE USED AS THE INITIAL MOTION...ESTIMATED AT 295/8. A TRACK BETWEEN WEST-NORTHWEST AND NORTHWEST IS EXPECTED FOR THE NEXT FEW DAYS AS KAREN MOVES AROUND THE SOUTHWESTERN SIDE OF A LOW TO MID-LEVEL RIDGE OVER THE CENTRAL ATLANTIC OCEAN. THEREAFTER A TURN TO A MORE WESTWARD MOTION IS POSSIBLE DUE TO RISING HEIGHTS TO THE NORTH OF KAREN. NUMERICAL GUIDANCE HAS BEEN MUCH TOO FAR TO THE RIGHT WITH THIS SYSTEM AND...GIVEN THE CONTINUED WEAK INTENSITY OF THE STORM...THE NHC FORECAST WILL LIE ON THE LEFT SIDE OF THE GUIDANCE ENVELOPE SIMILAR TO THE 18Z GFS. THE LARGE WESTWARD SHIFT AT 4 AND 5 DAYS IS MOSTLY DUE TO THE CENTER REFORMATION...AND NOT A HUGE CHANGE IN THE MODEL GUIDANCE. FORECAST POSITIONS AND MAX WINDS INITIAL 29/0300Z 16.2N 51.9W 35 KT 12HR VT 29/1200Z 17.0N 53.2W 35 KT 24HR VT 30/0000Z 18.2N 54.9W 30 KT 36HR VT 30/1200Z 19.5N 56.3W 25 KT 48HR VT 01/0000Z 20.7N 57.6W 25 KT 72HR VT 02/0000Z 23.0N 60.0W 30 KT 96HR VT 03/0000Z 24.5N 62.5W 30 KT 120HR VT 04/0000Z 25.5N 64.5W 30 KT $$ FORECASTER BLAKE |
