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| #546556 (Received by flhurricane at: 4:41 PM 29.Sep.2012) TCDAT4 HURRICANE NADINE DISCUSSION NUMBER 69 NWS NATIONAL HURRICANE CENTER MIAMI FL AL142012 500 PM AST SAT SEP 29 2012 ALTHOUGH ANALYSES FROM UW-CIMSS AND THE SHIPS MODEL CONTINUE TO SHOW 20 KT OF SOUTHWESTERLY VERTICAL WIND SHEAR...NADINE HAS CONTINUED TO BECOME BETTER ORGANIZED. THE EYE HAS BECOME MORE APPARENT IN VISIBLE AND INFRARED IMAGERY...AND THERE HAS BEEN AN INCREASE IN BANDING AROUND THE EYE. A RECENT SSM/IS OVERPASS SHOWS THAT THE EYE IS TILTED TOWARD THE NORTH...BUT THE TILT IS LESS THAN THIS TIME YESTERDAY. WHILE SATELLITE INTENSITY ESTIMATES ARE 65 KT FROM TAFB AND SAB...THE CIMSS ADT ESTIMATE IS NEAR 80 KT...THE LATEST AMSU ESTIMATES FROM CIMSS AND CIRA ARE IN THE 70-80 KT RANGE...AND THE LATEST CIMSS SATCON ESTIMATE IS 78 KT. BASED ON THIS...THE INITIAL INTENSITY IS INCREASED TO 70 KT...AND THIS COULD BE A LITTLE CONSERVATIVE. THE INITIAL MOTION IS 345/13. 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 96 HR. THE CANADIAN MODEL FORECASTS THE LARGEST LOOP...WITH THE CENTER OF NADINE MOVING SOUTHWARD TO 30N BEFORE TURNING EASTWARD. THE NEW FORECAST TRACK SHOWS MORE SOUTHWARD MOTION DURING THE LOOP THAN THE PREVIOUS FORECAST...BUT STILL NOT AS MUCH AS FORECAST BY THE DYNAMICAL MODELS. 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. NADINE DOES NOT APPEAR AS SHEARED AS THE CIMSS/SHIPS-ANALYZED SHEAR SUGGESTS...AND IT MAY BE THAT A MID-/UPPER-LEVEL TROUGH SHORTWAVE TROUGH JUST SOUTH OF THE SYSTEM IS PARTIALLY SHELTERING IT. THIS TROUGH COULD ALSO PROVIDE SOME FAVORABLE UPPER-LEVEL DIVERGENCE... AND THE INTENSITY FORECAST THUS CALLS FOR A LITTLE MORE STRENGTHENING DURING THE FIRST 12 HR. FROM 24-72 HR...NADINE COULD ENCOUNTER DECREASING SHEAR AS IT MERGES WITH THE MID-/UPPER-LEVEL LOW. HOWEVER...THIS MERGER IS LIKELY TO AT LEAST SOMEWHAT DISRUPT THE STRUCTURE...AND THE NEW INTENSITY FORECAST FOLLOWS THE PREVIOUS FORECAST IN CALLING FOR WEAKENING DURING THIS TIME. LATE IN THE FORECAST PERIOD...INTERACTION BETWEEN NADINE AND THE BAROCLINIC CYCLONE SHOULD LEAD TO EXTRATROPICAL TRANSITION. THE FORECAST CALLS FOR THIS AT 120 HR...ALTHOUGH IT COULD BE DELAYED IF NADINE IS SOUTH OF THE CURRENT FORECAST TRACK. FORECAST POSITIONS AND MAX WINDS INIT 29/2100Z 34.4N 36.7W 70 KT 80 MPH 12H 30/0600Z 35.8N 37.4W 75 KT 85 MPH 24H 30/1800Z 36.7N 38.2W 70 KT 80 MPH 36H 01/0600Z 36.5N 38.7W 65 KT 75 MPH 48H 01/1800Z 35.9N 39.0W 60 KT 70 MPH 72H 02/1800Z 35.0N 39.0W 55 KT 65 MPH 96H 03/1800Z 35.0N 37.0W 50 KT 60 MPH 120H 04/1800Z 38.5N 32.0W 45 KT 50 MPH...POST-TROP/EXTRATROP $$ FORECASTER BEVEN |
