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| #546447 (Received by flhurricane at: 4:59 AM 29.Sep.2012) TCDAT4 TROPICAL STORM NADINE DISCUSSION NUMBER 67 NWS NATIONAL HURRICANE CENTER MIAMI FL AL142012 500 AM AST SAT SEP 29 2012 IT APPEARS THAT VERTICAL SHEAR IS STARTING TO WEAKEN NADINE. ALMOST ALL OF DEEP CONVECTION IS NOW LOCATED NORTH OF THE CENTER...AND MICROWAVE IMAGES SHOW AN INCREASING SEPARATION BETWEEN THE LOW AND MID-LEVEL CENTERS. WITH THE DEGRADATION IN THE CLOUD PATTERN...THE INITIAL WIND SPEED IS REDUCED TO 60 KT...A BLEND OF THE T AND CI NUMBERS FROM TAFB AND SAB. WHILE THE SHEAR IS EXPECTED TO REMAIN MODERATE OVER THE NEXT DAY OR TWO...SSTS SHOULD DECREASE AS NADINE GAINS LATITUDE. NORMALLY THIS PATTERN WOULD CALL FOR ADDITIONAL WEAKENING...BUT UPPER-LEVEL TEMPERATURES ARE ALSO FORECAST TO COOL...WHICH COULD HELP THE CYCLONE KEEP ITS STRENGTH. VERY LITTLE CHANGE WAS MADE TO THE PREVIOUS FORECAST AFTER ACCOUNTING FOR THE SLIGHTLY WEAKER INITIAL STATE. A SERIES OF MICROWAVE PASSES GIVE A CONFIDENT INITIAL MOTION OF 340/10. THIS GENERAL MOTION IS EXPECTED FOR A DAY OR SO UNTIL STEERING CURRENTS BREAK DOWN TO THE NORTHWEST OF A SUBTROPICAL RIDGE. MODEL GUIDANCE OVERNIGHT IS GENERALLY SHOWING MORE INTERACTION BETWEEN NADINE AND A MID- TO UPPER-LEVEL TROUGH OVER THE CENTRAL ATLANTIC...WHICH CAUSES NADINE TO UNDERGO A CYCLONIC LOOP IN 2 TO 4 DAY TIME FRAME. THE ECMWF MODEL HAS BEEN FAIRLY CONSISTENTLY SHOWING THIS LOOP...AND NOW MOST OF THE MODELS SHOW IT BESIDES THE GFS AND GFS ENSEMBLE. THE OFFICIAL FORECAST IS TRENDED TOWARD THE MODEL CONSENSUS...SHOWING LITTLE CHANGE IN THE FIRST DAY OR SO...AND A SMALL SOUTHWARD LOOP IN THE MEDIUM RANGE. A RATHER LARGE TROUGH IS EXPECTED TO DEVELOP OVER THE NORTHERN ATLANTIC OCEAN AT BY DAY 5...WHICH WILL HOPEFULLY CAUSE NADINE TO FINALLY LEAVE THE SUBTROPICS. MOST OF THE MODELS ARE NOW SHOWING THE STORM BECOMING POST-TROPICAL BY DAY 5 DUE TO COLDER WATERS AND STRONGER SHEAR...BUT GIVEN PAST EXPERIENCE...I HAVE ELECTED NOT TO SHOW THIS TRANSITION YET. FORECAST POSITIONS AND MAX WINDS INIT 29/0900Z 31.9N 35.9W 60 KT 70 MPH 12H 29/1800Z 33.5N 36.5W 60 KT 70 MPH 24H 30/0600Z 35.4N 37.2W 60 KT 70 MPH 36H 30/1800Z 36.4N 37.8W 60 KT 70 MPH 48H 01/0600Z 36.2N 38.0W 55 KT 65 MPH 72H 02/0600Z 35.5N 37.5W 50 KT 60 MPH 96H 03/0600Z 35.5N 36.5W 45 KT 50 MPH 120H 04/0600Z 37.5N 33.5W 40 KT 45 MPH $$ FORECASTER BLAKE |
