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| #543369 (Received by flhurricane at: 4:41 AM 17.Sep.2012) TCDAT4 TROPICAL STORM NADINE DISCUSSION NUMBER 24 NWS NATIONAL HURRICANE CENTER MIAMI FL AL142012 500 AM AST MON SEP 17 2012 AIRMASS IMAGERY FROM EUMETSAT INDICATES THAT AN UPPER-LEVEL SHORTWAVE TROUGH IS NOW INTERACTING WITH NADINE...WITH A TONGUE OF DRY AIR WRAPPING AROUND THE SOUTH AND WEST SIDES OF THE CYCLONE. THIS HAS RESULTED IN A DECREASE IN THE CENTRAL CONVECTION AND AN INCREASE IN CONVECTIVE BANDING OVER THE NORTHERN SEMICIRCLE. SATELLITE INTENSITY ESTIMATES ARE TROPICAL 65 KT FROM TAFB AND SUBTROPICAL 55-65 KT FROM SAB. A RECENT OSCAT OVERPASS SHOWED SEVERAL 55 KT WIND VECTORS TO THE SOUTH AND SOUTHEAST OF THE CENTER...WHILE RECENT CIMSS AMSU INTENSITY ESTIMATES WERE 77-79 KT. THE INITIAL INTENSITY REMAINS 60 KT BASED ON A BLEND OF THESE DATA. THE INITIAL MOTION IS NOW 065/15. AN ADDITIONAL REDUCTION IN FORWARD SPEED AND A TURN TOWARD THE NORTH-NORTHEAST ARE EXPECTED DURING THE NEXT DAY OR TWO AS A MID-LEVEL RIDGE SLIDES EASTWARD TO THE NORTH OF NADINE...AND A CUT-OFF LOW FORMS TO THE WEST OF THE CYCLONE. THE MODEL GUIDANCE IS IN GOOD AGREEMENT DURING THE FIRST 48-72 HR...AND THIS PART OF THE NEW FORECAST IS LITTLE CHANGED FROM THE PREVIOUS ADVISORY. AFTER THAT TIME...ANOTHER MID-/UPPER-LEVEL LOW IS FORECAST TO MOVE SOUTHWARD OVER THE NORTHEASTERN ATLANTIC TOWARD NADINE...WITH THE TWO SYSTEMS LIKELY TO STRONGLY INTERACT AFTER 96 HR. AS THIS OCCURS...THE DYNAMICAL GUIDANCE BECOMES QUITE DIVERGENT DUE TO THE DIFFERENCES IN HOW THEY DEPICT THIS INTERACTION. GIVEN THE UNCERTAINTY...THE NEW TRACK FORECAST FOLLOWS THE TREND OF THE PREVIOUS FORECAST IN SHOWING A SLOW MOTION...WHICH SMOOTHS THROUGH SOME POSSIBLY VERY ERRATIC MOTION DURING THIS TIME. THE GLOBAL MODELS FORECAST THAT NADINE WILL INTERACT WITH THE CURRENT UPPER-LEVEL TROUGH...AND A SECOND TROUGH APPROACHING FROM THE WEST...DURING THE NEXT 48 HR. THESE INTERACTIONS SHOULD CAUSE NADINE TO INGEST UPPER-LEVEL COOL/DRY AIR...WHICH COULD START EXTRATROPICAL TRANSITION. HOWEVER...THE GLOBAL MODELS AGREE THAT THERE IS NOT ENOUGH COLD AIR TO COMPLETE TRANSITION...AND THEY MAINTAIN NADINE AS A WARM-CORE SYSTEM THROUGH AT LEAST 96 HR... POSSIBLY WITH SOME HYBRID CHARACTERISTICS. THE FORECAST OF NADINE BECOMING EXTRATROPICAL AT 120 HR IS BASED ON THE PREMISE THAT INTERACTION WITH THE NORTH ATLANTIC LOW WILL BRING A LARGER BATCH OF COLD AIR INTO THE SYSTEM. HOWEVER...THIS IS A LOW CONFIDENCE TRANSITION FORECAST. REGARDLESS OF WHETHER THE CYCLONE IS TROPICAL...EXTRATROPICAL...OR HYBRID...ALL OF THE INTENSITY GUIDANCE FORECASTS NADINE TO REMAIN A LARGE AND VIGOROUS SYSTEM OVER THE NORTHEASTERN ATLANTIC THROUGH THE FORECAST PERIOD. FORECAST POSITIONS AND MAX WINDS INIT 17/0900Z 32.0N 36.4W 60 KT 70 MPH 12H 17/1800Z 32.8N 34.7W 55 KT 65 MPH 24H 18/0600Z 34.0N 33.2W 55 KT 65 MPH 36H 18/1800Z 35.2N 32.5W 55 KT 65 MPH 48H 19/0600Z 36.3N 32.2W 55 KT 65 MPH 72H 20/0600Z 37.0N 31.0W 50 KT 60 MPH 96H 21/0600Z 37.0N 29.0W 50 KT 60 MPH 120H 22/0600Z 37.0N 27.0W 50 KT 60 MPH...POST-TROP/EXTRATROP $$ FORECASTER BEVEN |
