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| #152858 (Received by flhurricane at: 10:49 AM 28.Sep.2007) TCDAT2 TROPICAL STORM KAREN DISCUSSION NUMBER 15 NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL AL122007 1100 AM EDT FRI SEP 28 2007 VISIBLE IMAGERY SUGGESTS THAT THE WEAKENING CIRCULATION OF KAREN HAS MOVED ERRATICALLY THIS MORNING...BUT NOW APPEARS TO BE RETURNING TO A PREVIOUS WEST-NORTHWESTWARD MOTION. AN EARLIER 0910Z QUIKSCAT OVERPASS INDICATED THAT THERE WAS A SMALL AREA OF BELIEVABLE FLAGGED 40 KT WINDS IN THE NORTHEAST QUADRANT. BUT SINCE THEN...THAT CONVECTIVE AREA CONTAINING THE COLDEST TOPS HAS DIMINISHED CONSIDERABLY. BASED ON THE QUIKSCAT INTERPRETATION AND CURRENT SATELLITE INTENSITY ESTIMATES OF 35 KT...THE INITIAL INTENSITY IS LOWERED TO 35 KT...AND THIS COULD BE GENEROUS. PERSISTENTLY STRONG SOUTHWESTERLY SHEAR IS EXPECTED TO AFFECT KAREN DURING THE NEXT 72 HOURS OR SO. THEREAFTER...THE INTENSITY GUIDANCE AGREES IN BRINGING UNFAVORABLE UPPER-LEVEL NORTHWESTERLY WINDS OVER THE SYSTEM. THE OFFICIAL FORECAST INDICATES WEAKENING TO A DEPRESSION IN 12 HOURS...FOLLOWING THE SHIPS AND LGEM. AFTERWARD...BECAUSE OF THE POTENTIAL OF INTERMITTENT BURSTS OF DEEP CONVECTION NEAR THE CENTER...THE FORECAST SHOWS LITTLE CHANGE IN STRENGTH. HOWEVER...KAREN COULD BECOME A REMNANT LOW IN 36 HOURS...AS INDICATED BY BOTH AFOREMENTIONED INTENSITY MODELS. IN PREVIOUS RUNS...DESPITE THE OBVIOUS UNFAVORABLE UPPER LEVEL WIND ENVIRONMENT...SOME DYNAMICAL MODELS SUGGESTED SIGNIFICANT STRENGTHENING. HOWEVER...IN THE LATEST RUNS...THE GFS WEAKENS KAREN AND THIS IS A MORE REALISTIC SCENARIO. ECMWF AND GFDL INSIST ON STRENGTHENING. WE SHALL SEE IN THE NEXT RUN IF THESE MODELS COME TO AN AGREEMENT WITH THE GFS. INITIAL MOTION IS ESTIMATED AT 295/8. A LOW- TO MID LEVEL TROPOSPHERIC SUBTROPICAL RIDGE TO THE NORTH OF KAREN SHOULD MAINTAIN A WEST-NORTHWESTWARD MOTION DURING THE NEXT 2 DAYS. AFTERWARD...A DEVELOPING WEAKNESS IN THE RIDGE NORTHWEST OF THE CYCLONE SHOULD TEMPORARILY INDUCE A MORE NORTHWESTWARD MOTION. AROUND THE 96 HOUR PERIOD...ALL OF THE DYNAMICAL MODELS ARE INDICATING THAT THE TROUGH WILL FILL AND MOVE NORTHEAST ALLOWING A MID- LEVEL HIGH TO BUILD SOUTHEAST OF BERMUDA. THIS CHANGE IN THE STEERING PATTERN SHOULD CAUSE KAREN TO TURN MORE TO THE WEST...IF THE CYCLONE SURVIVES FOR THAT LONG OF A PERIOD. THE OFFICIAL TRACK FORECAST IS CLOSE TO THE PREVIOUS PACKAGE AND IS BASED ON A BLEND OF THE MODEL CONSENSUS...AND HEDGES TOWARD THE SHALLOW MEAN LAYER BAM....SINCE THE KAREN IS FORECAST TO WEAKEN. FORECAST POSITIONS AND MAX WINDS INITIAL 28/1500Z 15.1N 49.2W 35 KT 12HR VT 29/0000Z 15.5N 50.5W 30 KT 24HR VT 29/1200Z 16.6N 52.0W 30 KT 36HR VT 30/0000Z 17.6N 53.3W 30 KT 48HR VT 30/1200Z 18.5N 54.6W 30 KT 72HR VT 01/1200Z 20.0N 56.5W 30 KT 96HR VT 02/1200Z 21.5N 58.0W 30 KT 120HR VT 03/1200Z 22.0N 60.0W 30 KT $$ FORECASTER ROBERTS |
