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| #294980 (Received by flhurricane at: 10:37 PM 11.Sep.2009) TCDAT2 TROPICAL STORM FRED DISCUSSION NUMBER 18 NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL AL072009 1100 PM AST FRI SEP 11 2009 FRED CONTINUES TO PRODUCE DEEP CONVECTION...ALTHOUGH THE COLDEST CLOUD TOPS ARE NOW DISPLACED MORE THAN A DEGREE NORTH OF THE LOW-LEVEL CENTER. THIS DISPLACEMENT IS DUE TO ABOUT 20 KNOTS OF SOUTHERLY SHEAR AS ANALYZED BY THE SHIPS MODEL AND UW-CIMSS. DVORAK DATA T-NUMBERS AT 0000 UTC WERE 2.5 FROM SAB AND 3.0 FROM TAFB... AND A QUIKSCAT PASS FROM AROUND 2100 UTC DID NOT SHOW ANY WINDS HIGHER THAN ABOUT 45 KNOTS. THE INITIAL INTENSITY OF 50 KNOTS IS BASED ON A BLEND OF THE DATA-T NUMBERS AND ASSUMES THAT RAIN WAS ATTENUATING THE WIND SIGNAL SOMEWHAT IN THE QUIKSCAT DATA. WITH THE WIND SHEAR EXPECTED TO CONTINUE...AND FRED MOVING OVER MARGINAL SSTS AND INTO A MORE STABLE ENVIRONMENT...GRADUAL WEAKENING IS EXPECTED THROUGH THE PERIOD. THE OFFICIAL FORECAST HAS BEEN ADJUSTED DOWNWARD FOR THE FIRST 24 HOURS TO ACCOUNT FOR THE INITIAL INTENSITY...AND IS SIMILAR TO THE PREVIOUS FORECAST AFTER THAT TIME...IN BEST AGREEMENT WITH THE LGEM MODEL. IT IS POSSIBLE THAT FRED COULD DISSIPATE BEFORE THE END OF THE 5-DAY PERIOD...AS INDICATED BY THE SHIPS MODEL. A 2016 UTC SSMI PASS...A 1941 UTC SSMIS PASS...AND THE QUIKSCAT DATA ALL SUGGEST THAT THE LOW-LEVEL CENTER OF FRED IS LOCATED FARTHER SOUTHEAST THAN PREVIOUSLY ESTIMATED. THE INITIAL MOTION ESTIMATE IS VERY SLOW...060/02. A TURN TOWARD THE NORTH AND THE NORTHWEST WITH A GRADUAL INCREASE IN FORWARD SPEED IS EXPECTED OVER THE NEXT COUPLE OF DAYS AS THE DEEP-LAYER TROUGH OVER THE NORTH ATLANTIC BEGINS TO LIFT OUT. BY 72 HOURS...LOW- TO MID-LEVEL RIDGING WILL BUILD IN TO THE NORTH OF WHAT IS LEFT OF FRED...AND SHOULD IMPART A FASTER MOTION TOWARD THE WEST-NORTHWEST THROUGH THE END OF THE PERIOD. THE TRACK MODEL GUIDANCE IS IN GOOD AGREEMENT ON THIS SCENARIO...WITH THE EXCEPTION OF THE UKMET...WHICH IS A FAR SOUTHERN OUTLIER. THE NEW OFFICIAL FORECAST IS ADJUSTED TO THE RIGHT OF THE PREVIOUS TRACK DUE TO THE MORE EASTWARD INITIAL POSITION...AND IS NEAR OR JUST TO THE RIGHT OF THE TVCN MODEL CONSENSUS. THE INITIAL 34-KT AND 50-KT WIND RADII WERE ADJUSTED BASED ON THE QUIKSCAT DATA. FORECAST POSITIONS AND MAX WINDS INITIAL 12/0300Z 18.0N 33.6W 50 KT 12HR VT 12/1200Z 18.1N 33.5W 40 KT 24HR VT 13/0000Z 18.4N 33.6W 40 KT 36HR VT 13/1200Z 19.2N 34.4W 35 KT 48HR VT 14/0000Z 20.0N 35.9W 30 KT 72HR VT 15/0000Z 22.0N 40.5W 25 KT...REMNANT LOW 96HR VT 16/0000Z 23.5N 46.0W 20 KT...REMNANT LOW 120HR VT 17/0000Z 25.0N 51.5W 20 KT...REMNANT LOW $$ FORECASTER BRENNAN |
