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| #546506 (Received by flhurricane at: 10:44 AM 29.Sep.2012) TCDAT4 HURRICANE NADINE DISCUSSION NUMBER 68 NWS NATIONAL HURRICANE CENTER MIAMI FL AL142012 1100 AM AST SAT SEP 29 2012 ALTHOUGH ANALYSES FROM CIMSS AND THE SHIPS MODEL CONTINUE TO SHOW 20 KT OF SOUTHWESTERLY VERTICAL WIND SHEAR...NADINE HAS BECOME BETTER ORGANIZED DURING THE PAST SEVERAL HOURS. AN EYE HAS RE-APPEARED IN VISIBLE IMAGERY...AND AN SSM/IS OVERPASS AT 1112 UTC SHOWED THAT THE LOW- AND MID-LEVEL CENTERS ARE NOW MORE VERTICALLY ALIGNED. SATELLITE INTENSITY ESTIMATES FROM TAFB AND SAB ARE 65 KT. ALSO...CIMSS ADT ESTIMATES ARE NEAR 80 KT...AND A RECENT CIMSS AMSU ESTIMATE IS 64 KT. BASED ON THESE...THE INITIAL INTENSITY IS INCREASED TO 65 KT. THE INITIAL MOTION IS NOW 345/12. NADINE IS BETWEEN A DEEP-LAYER RIDGE TO THE EAST AND A MID/UPPER-LEVEL LOW TO THE WEST. THE GLOBAL MODELS FORECAST THE CYCLONE TO MERGE WITH THE LOW BETWEEN 24-72 HR...WITH THE SYSTEM THEN CAUGHT IN AN AREA OF LIGHT STEERING CURRENTS. THE DYNAMICAL MODELS ARE IN GOOD AGREEMENT THAT NADINE WILL SLOW DOWN AND MAKE A CYCLONIC LOOP DURING THE NEXT 72-96 HR. THE CANADIAN MODEL FORECASTS THE LARGEST LOOP...WITH THE CENTER OF NADINE MOVING SOUTH OF 30N BEFORE TURNING EASTWARD. THE NEW FORECAST TRACK FOLLOWS THE LOOP SCENARIO...BUT TO KEEP CONTINUITY WITH THE PREVIOUS FORECAST IT SHOWS LESS OF A SOUTHWARD MOTION THAN INDICATED BY THE GUIDANCE. AFTER 96 HR...THE GLOBAL MODELS FORECAST A LARGE BAROCLINIC CYCLONE TO DEVELOP OVER THE NORTHEASTERN ATLANTIC WITH THE ASSOCIATED WESTERLY WINDS EXTENDING SOUTHWARD TO AT LEAST 30N. THIS SYSTEM SHOULD STEER NADINE TO THE EAST OR NORTHEAST NEAR THE END OF THE FORECAST PERIOD. WATER VAPOR IMAGERY SHOWS A SHORTWAVE TROUGH THAT IS ROTATING AROUND THE MID/UPPER-LEVEL LOW IS NOW APPROACHING NADINE FROM THE SOUTH. IT IS POSSIBLE THIS SYSTEM WILL PROVIDE SOME UPPER-LEVEL DIVERGENCE TO MAINTAIN THE CURRENT INTENSITY DESPITE THE SHEAR...SO THE NEW INTENSITY FORECAST KEEPS NADINE A HURRICANE THROUGH 24 HR. NADINE COULD ENCOUNTER DECREASING SHEAR AS IT MERGES WITH THE LOW. HOWEVER...THE GUIDANCE IS IN POOR AGREEMENT ON THE DETAILS...WITH THE GFS SHOWING CYCLONIC UPPER-LEVEL FLOW AROUND THE STORM AT 36 HR AND THE ECMWF SHOWING ANTICYCLONIC FLOW. THE INTENSITY FORECAST SHOWS SOME WEAKENING DURING THE MERGER BASED ON THE PREMISE THAT IT WILL AT LEAST SOMEWHAT DISRUPT THE STRUCTURE OF NADINE. LATE IN THE FORECAST PERIOD...INTERACTION BETWEEN NADINE AND THE BAROCLINIC CYCLONE SHOULD LEAD TO EXTRATROPICAL TRANSITION. THE FORECAST NOW CALLS FOR THIS AT 120 HR...ALTHOUGH IT COULD BE DELAYED IF NADINE IS SOUTH OF THE CURRENT FORECAST POSITION. FORECAST POSITIONS AND MAX WINDS INIT 29/1500Z 33.3N 36.2W 65 KT 75 MPH 12H 30/0000Z 34.8N 36.7W 65 KT 75 MPH 24H 30/1200Z 36.4N 37.5W 65 KT 75 MPH 36H 01/0000Z 36.7N 38.1W 60 KT 70 MPH 48H 01/1200Z 36.3N 38.1W 55 KT 65 MPH 72H 02/1200Z 35.5N 38.0W 55 KT 65 MPH 96H 03/1200Z 35.5N 36.5W 50 KT 60 MPH 120H 04/1200Z 38.0N 33.0W 45 KT 50 MPH...POST-TROP/EXTRATROP $$ FORECASTER BEVEN |
