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| #542269 (Received by flhurricane at: 4:44 AM 12.Sep.2012) TCDAT4 TROPICAL STORM NADINE DISCUSSION NUMBER 4 NWS NATIONAL HURRICANE CENTER MIAMI FL AL142012 500 AM AST WED SEP 12 2012 NADINE CONTINUES TO BECOME BETTER ORGANIZED WITH THE FORMATION OF A CENTRAL DENSE OVERCAST AND AN OUTER CONVECTIVE BAND IN THE SOUTHEASTERN SEMICIRCLE. SATELLITE INTENSITY ESTIMATES ARE 45 KT FROM SAB AND 35 KT FROM TAFB. IN ADDITION...RECENT AUTOMATED DVORAK INTENSITY ESTIMATES FROM CIMSS ARE NEAR 45 KT. THE INITIAL INTENSITY IS INCREASED TO 40 KT...AND THIS COULD BE A LITTLE CONSERVATIVE. THE INITIAL MOTION IS 300/15. NADINE IS MOVING TOWARD A SIGNIFICANT BREAK IN THE SUBTROPICAL RIDGE OVER THE CENTRAL NORTH ATLANTIC. THE GLOBAL MODELS FORECAST THIS BREAK TO BECOME EVEN MORE PRONOUNCED BY 72 HR AS A DEEP-LAYER LOW PRESSURE SYSTEM FORMS NEAR OR NORTH OF BERMUDA. THIS EVOLUTION SHOULD STEER NADINE GENERALLY NORTHWESTWARD FOR 36 HR OR SO...FOLLOWED BY A TURN TOWARD THE NORTH. THIS PART OF THE NEW FORECAST TRACK IS SIMILAR TO THE PREVIOUS TRACK AND LIES JUST TO THE RIGHT OF THE CONSENSUS MODELS. AFTER 72 HR...THE SUBTROPICAL RIDGE IS FORECAST TO BUILD ALONG 20N...LEAVING NADINE IN WESTERLY OR SOUTHWESTERLY FLOW ON THE NORTH SIDE OF THE RIDGE. THE TRACK GUIDANCE BECOMES MORE DIVERGENT DURING THIS PERIOD. THE UKMET SHOWS NADINE GOING NORTHWARD AND BECOMING ENTANGLED WITH THE DEEP-LAYER LOW...WHILE THE GFS SHOWS AN EASTWARD MOTION. THE OTHER DYNAMICAL MODELS ARE SPREAD BETWEEN THESE EXTREMES. THIS PORTION OF THE NEW FORECAST TRACK IS SHIFTED A LITTLE NORTH OF THE PREVIOUS TRACK...BUT LIES TO THE SOUTH OF THE CONSENSUS MODELS AND THE CENTER OF THE TRACK GUIDANCE ENVELOPE. OVERALL...THE NEW FORECAST TRACK IS IN BEST AGREEMENT WITH THE FLORIDA STATE SUPERENSEMBLE. NADINE IS CURRENTLY IN AN ENVIRONMENT OF LIGHT VERTICAL WIND SHEAR WITH GOOD TO EXCELLENT CIRRUS OUTFLOW IN ALL DIRECTIONS. THE QUESTION IS HOW LONG WILL THE FAVORABLE CONDITIONS LAST? THE SHIPS MODEL FORECASTS WESTERLY SHEAR OF ABOUT 15 KT TO DEVELOP WITHIN 24 HR...ALTHOUGH THE SOURCE OF THIS IS NOT READILY APPARENT IN THE GFS MODEL FIELDS. THE SHIPS AND LGEM MODELS SHOW NADINE BECOMING A HURRICANE IN 36-48 HR DESPITE THE SHEAR FORECAST...SO THE NEW INTENSITY FORECAST DOES LIKEWISE. THERE IS AN ALTERNATIVE SCENARIO FOR THIS PORTION OF THE INTENSITY FORECAST...WHICH IS THE SHEAR DOES NOT OCCUR AND NADINE RAPIDLY STRENGTHENS. THIS IS SOMEWHAT SUPPORTED BY THE RAPID INTENSIFICATION INDEX OF THE SHIPS MODEL... WHICH SHOWS ABOUT A 40 PERCENT CHANCE OF RAPID INTENSIFICATION DURING THE NEXT 24 HOURS. REGARDLESS OF WHAT HAPPENS IN THE SHORT TERM...FROM 72-120 HR NADINE IS LIKELY TO ENCOUNTER AT LEAST 20-25 KT OF WESTERLY SHEAR NORTH OF THE SUBTROPICAL RIDGE AXIS...WHICH SHOULD STOP INTENSIFICATION AND START A WEAKENING TREND. FORECAST POSITIONS AND MAX WINDS INIT 12/0900Z 18.6N 46.6W 40 KT 45 MPH 12H 12/1800Z 19.7N 48.5W 50 KT 60 MPH 24H 13/0600Z 21.4N 50.6W 60 KT 70 MPH 36H 13/1800Z 23.3N 52.6W 65 KT 75 MPH 48H 14/0600Z 25.4N 53.8W 70 KT 80 MPH 72H 15/0600Z 29.0N 54.0W 75 KT 85 MPH 96H 16/0600Z 31.0N 51.0W 70 KT 80 MPH 120H 17/0600Z 32.5N 46.5W 65 KT 75 MPH $$ FORECASTER BEVEN |
