000 WTNT44 KNHC 210246 TCDAT4 TROPICAL STORM NADINE DISCUSSION NUMBER 39 NWS NATIONAL HURRICANE CENTER MIAMI FL AL142012 1100 PM AST THU SEP 20 2012 SATELLITE IMAGES INDICATE THAT RELATIVELY DEEP CONVECTION HAS BEEN INCREASING NORTHWEST OF THE CENTER OF NADINE DURING THE PAST SEVERAL HOURS. THE INCREASE IN CONVECTION...HOWEVER...IS LIKELY RELATED TO BAROCLINIC INFLUENCES SINCE SURFACE OBSERVATIONS FROM THE AZORES AND AN 2224 UTC ASCAT PASS INDICATE A FRONTAL ZONE IMPINGING ON THE CORE OF THE TROPICAL CYCLONE. THE INITIAL INTENSITY ESTIMATE IS INCREASED TO 55 KT IN AGREEMENT WITH THE EARLIER ASCAT DATA WHICH SHOWED SEVERAL 50 KT UNCONTAMINATED WIND BARBS NORTHWEST OF THE CENTER. THESE STRONGER WINDS ARE PRESUMABLY RELATED TO AN INCREASE IN THE PRESSURE GRADIENT ON THE NORTHWEST SIDE OF THE STORM. SATELLITE AND MICROWAVE DATA SUGGEST THAT THE TRACK OF NADINE MAY BE VEERING MORE SOUTHEASTERLY...BUT A LONGER-TERM INITIAL MOTION ESTIMATE IS 120/08. LARGE-SCALE MODELS ARE IN REASONABLY GOOD AGREEMENT THAT NADINE WILL BE STEERED SOUTHEASTWARD AND SLOW DOWN THROUGH 36-48 HOURS. AFTER THIS TIME...THERE REMAINS A LARGE SPREAD IN THE TRACK GUIDANCE. AS IN THE LAST FEW RUNS...THE GFS SHOWS MORE INTERACTION WITH THE MID- TO UPPER-LEVEL TROUGH PASSING NORTH OF THE STORM WHICH RESULTS IN NADINE MOVING MORE RAPIDLY EAST-NORTHEASTWARD. ON THE OTHER HAND...THE ECMWF/UK MET HAVE A SLIGHTLY MORE PROGRESSIVE TROUGH WITH LESS AMPLITUDE AND EITHER KEEP NADINE MEANDERING OR MOVING MORE SLOWLY TOWARD THE NORTHEAST THAN THE GFS. SINCE THERE CONTINUES TO BE A STARK DICHOTOMY IN THE GFS/ECMWF ENSEMBLE MEMBERS...ONLY A SLOW MOVEMENT TOWARD THE EAST IS DEPICTED DURING THE 3 TO 5 DAY TIME FRAME. GLOBAL MODELS SHOW NADINE ATTEMPTING TO OUTRUN THE BAROCLINIC ZONE ENCROACHING ON IT DURING THE NEXT DAY OR TWO...BUT THIS MAY BE OPTIMISTIC GIVEN THE CURRENT SEPARATION BETWEEN THESE TWO FEATURES. THE TRANSITION TO A POST-TROPICAL LOW COULD NOW BE MORE IMMINENT...AND POST-TROPICAL STATUS IS FORECAST TO OCCUR SOONER THAN IN THE PREVIOUS ADVISORY. THEN AGAIN...NADINE COULD TEMPORARILY FIND ITSELF SECLUDED FROM THE BAROCLINIC ENVIRONMENT...OVER RELATIVELY WARMER WATERS...AND IN A MORE UNSTABLE ENVIRONMENT DUE TO A STEEPENING OF LAPSE RATES. GIVEN THE CURRENT SATELLITE APPEARANCE OF NADINE...THE LATTER POSSIBILITY IS TREATED AS A LOWER PROBABILITY ALTERNATE SCENARIO. FORECAST POSITIONS AND MAX WINDS INIT 21/0300Z 35.4N 28.0W 55 KT 65 MPH 12H 21/1200Z 34.5N 27.1W 55 KT 65 MPH 24H 22/0000Z 33.2N 26.1W 55 KT 65 MPH...POST-TROPICAL 36H 22/1200Z 32.5N 25.1W 50 KT 60 MPH...POST-TROPICAL 48H 23/0000Z 32.4N 24.3W 50 KT 60 MPH...POST-TROPICAL 72H 24/0000Z 32.4N 24.0W 50 KT 60 MPH...POST-TROPICAL 96H 25/0000Z 32.4N 23.9W 50 KT 60 MPH...POST-TROPICAL 120H 26/0000Z 32.4N 23.8W 50 KT 60 MPH...POST-TROPICAL $$ FORECASTER KIMBERLAIN/BROWN