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| #543148 (Received by flhurricane at: 4:50 AM 16.Sep.2012) TCDAT4 HURRICANE NADINE DISCUSSION NUMBER 20 NWS NATIONAL HURRICANE CENTER MIAMI FL AL142012 500 AM AST SUN SEP 16 2012 NADINE LOOKS A LITTLE RAGGED IN SATELLITE IMAGERY THIS MORNING...AS THE CENTRAL CONVECTION LOOKS MORE SHEARED THAN IT DID EARLIER. AN AMSU OVERPASS AT 0448 UTC SUGGESTS THAT THE SYSTEM REMAINS TILTED VERTICALLY...WITH THE MID-LEVEL CENTER DISPLACED EAST OF THE LOW-LEVEL CENTER DUE TO 25 KT OF WESTERLY VERTICAL WIND SHEAR. SATELLITE INTENSITY ESTIMATES ARE 77 KT FROM SAB AND 65 KT FROM TAFB...AND AN AMSU-BASED INTENSITY ESTIMATE FROM CIMSS IS 72 KT. BASED ON THESE DATA...THE INITIAL INTENSITY REMAINS 70 KT. THE INITIAL MOTION REMAINS 095/15. NADINE IS EMBEDDED IN MID-/UPPER-LEVEL WESTERLY FLOW THAT SHOULD CONTINUE TO STEER THE CYCLONE EASTWARD FOR THE NEXT 12-24 HR. AFTER THAT TIME...THE GLOBAL MODELS AGREE ON THE FORMATION OF A DEEP-LAYER LOW WEST OF NADINE...WHICH SHOULD CAUSE THE CYCLONE TO TURN NORTHEASTWARD. NEAR THE END OF THE FORECAST PERIOD...THE MODELS DIVERGE ON THE INTERACTION OF NADINE WITH AN MID-/UPPER-LEVEL LOW OVER THE NORTHEASTERN ATLANTIC. THE ECMWF...CANADIAN...AND NOGAPS SHOW NADINE TRYING TO MERGE WITH THIS LOW. THE GFS DOES NOT SHOW A MERGER AND TRAPS NADINE SOUTH OF A BUILDING RIDGE. THE UKMET SHOWS THE LOW MOVING FARTHER EAST THAN THE ECMWF/CANADIAN/NOGAPS...AND AS A RESULT...FORECASTS NADINE TO MOVE MUCH FARTHER TO THE EAST THAN THE OTHER MODELS. GIVEN THE UNCERTAINTY AND THE SPREAD IN THE TRACK GUIDANCE BY 120 HR...THE NEW TRACK FORECAST FOLLOWS THE PREVIOUS FORECAST IN SHOWING A SLOW MOTION. OVERALL...THE NEW TRACK FORECAST IS SIMILAR TO THE PREVIOUS FORECAST AND LIES NEAR THE CENTER OF THE TRACK GUIDANCE ENVELOPE. THE INTENSITY FORECAST IS FULL OF ISSUES. THE FIRST IS THE WESTERLY SHEAR...WHICH LIKELY SHOULD CONTINUE FOR THE NEXT 24 HR AND COULD CAUSE WEAKENING. THE SECOND IS THAT THE GLOBAL MODELS FORECAST TWO UPPER-LEVEL SHORTWAVE TROUGHS WEST OF NADINE TO OVERTAKE THE HURRICANE BETWEEN 24-72 HR. THIS COULD DECREASE THE SHEAR... PROVIDE AN IMPROVED OUTFLOW...AND PERMIT SOME INTENSIFICATION. THE THIRD IS THE POSSIBILITY OF A MERGER WITH THE UPPER-LEVEL LOW NEAR 120 HR...WHICH...IF IT OCCURS...WOULD SIGNIFICANTLY CHANGE THE STRUCTURE OF NADINE. FINALLY...THE FORECAST TRACK TAKES THE CYCLONE OVER DECREASING SEA SURFACE TEMPERATURES. DESPITE THIS COMPLEXITY...THE INTENSITY GUIDANCE IS IN RELATIVELY GOOD AGREEMENT THAT NADINE SHOULD CHANGE LITTLE IN STRENGTH DURING THE NEXT 48 HR...FOLLOWED BY A SLOW WEAKENING. THE NEW INTENSITY FORECAST FOLLOWS THAT SCENARIO AND IS UNCHANGED FROM THE PREVIOUS FORECAST. IT IS ALSO IN GOOD AGREEMENT WITH THE SHIPS...LGEM...AND THE INTENSITY CONSENSUS. FORECAST POSITIONS AND MAX WINDS INIT 16/0900Z 30.5N 44.7W 70 KT 80 MPH 12H 16/1800Z 30.5N 42.0W 70 KT 80 MPH 24H 17/0600Z 31.3N 38.6W 70 KT 80 MPH 36H 17/1800Z 32.3N 36.0W 65 KT 75 MPH 48H 18/0600Z 33.5N 34.3W 65 KT 75 MPH 72H 19/0600Z 36.0N 32.5W 60 KT 70 MPH 96H 20/0600Z 36.5N 32.0W 55 KT 65 MPH 120H 21/0600Z 36.5N 31.5W 50 KT 60 MPH $$ FORECASTER BEVEN |
