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| #542476 (Received by flhurricane at: 4:47 AM 13.Sep.2012) TCDAT4 TROPICAL STORM NADINE DISCUSSION NUMBER 8 NWS NATIONAL HURRICANE CENTER MIAMI FL AL142012 500 AM AST THU SEP 13 2012 THE OVERALL APPEARANCE OF NADINE IN INFRARED IMAGERY HAS CHANGED LITTLE DURING THE PAST SEVERAL HOURS. A RECENT AMSU IMAGE SHOWS A MID-LEVEL EYE DISPLACED TO THE EAST-NORTHEAST OF OF THE APPARENT LOW-LEVEL CENTER. THIS MAY BE DUE TO 10-20 KT OF SOUTHWESTERLY VERTICAL WIND SHEAR DIAGNOSED BY THE SHIPS MODEL AND ANALYSES FROM CIMSS. SATELLITE INTENSITY ESTIMATES ARE 55 KT FROM TAFB AND SAB...AND A ASCAT OVERPASS RECEIVED JUST AFTER THE PREVIOUS ADVISORY SUPPORTS WINDS OF AT LEAST 55-60 KT. BASED ON THESE DATA...THE INITIAL INTENSITY REMAINS 60 KT. THE INITIAL WIND RADII HAVE BEEN REVISED A LITTLE BASED ON THE ASCAT DATA. THE INITIAL MOTION IS 305/14. NADINE IS MOVING TOWARD A BREAK IN THE SUBTROPICAL RIDGE...AND DURING THE NEXT 48 HR THE GUIDANCE IS IN GOOD AGREEMENT THAT THE CYCLONE SHOULD RECURVE AROUND THE WESTERN END OF THE RIDGE INTO THE WESTERLIES. THIS PART OF THE FORECAST TRACK IS SIMILAR TO THE PREVIOUS TRACK. AFTER 48 HR...THE GUIDANCE BECOMES SERIOUSLY DIVERGENT. THE GFDL FORECASTS A NORTHWARD MOVEMENT TOWARD NEWFOUNDLAND...WHILE THE GFS AND ECMWF FORECAST A GENERALLY EASTWARD MOTION. THE OTHER DYNAMICAL AND CONSENSUS MODELS ARE SPREAD BETWEEN THESE EXTREMES. THIS SPREAD SEEMS TO RESULT FROM HOW THE MODELS HANDLE THE INTERACTIONS BETWEEN NADINE...A DEEP-LAYER LOW FORECAST TO BE TO ITS EAST...AND A MID/UPPER-LEVEL TROUGH FORECAST TO BE IN THE WESTERLIES NEAR NEWFOUNDLAND. AT THIS TIME...IT IS NOT CLEAR WHICH OF THE MODELS HAS THE BEST HANDLE ON THESE INTERACTIONS. THEREFORE...THE FORECAST TRACK IS NUDGED ONLY SLIGHTLY NORTHWARD...AND IT LIES NEAR THE SOUTHERN EDGE OF THE GUIDANCE ENVELOPE IN BEST AGREEMENT WITH THE GFS...ECMWF...AND FLORIDA STATE SUPERENSEMBLE. ADDITIONAL ADJUSTMENTS OF THIS PART OF THE TRACK MAY BE NECESSARY WHEN THE MODELS COME INTO BETTER AGREEMENT. THE WINDOW FOR NADINE TO STRENGTHEN MAY BE CLOSING. IN ADDITION TO THE CURRENT INCREASE IN SHEAR...WATER VAPOR IMAGERY SHOWS MID/UPPER-LEVEL DRY AIR IMPINGING ON THE CYCLONE FROM THE SOUTHWEST. DESPITE THE LESS FAVORABLE ENVIRONMENT...MOST OF THE INTENSITY GUIDANCE SHOWS SOME STRENGTHENING DURING THE NEXT 24 HR...AND THE NEW FORECAST CALLS FOR NADINE TO BECOME A HURRICANE DURING THAT TIME. AFTER 24 HR...THE DYNAMICAL MODELS ARE IN GOOD AGREEMENT THAT NADINE WILL ENCOUNTER AT LEAST 20-30 KT OF WESTERLY SHEAR...WHICH SHOULD CAUSE SOME WEAKENING. THERE ARE HINTS THAT THE SHEAR COULD SUBSIDE AFTER 72 HR...BUT DUE TO THE UNCERTAINTY OF HOW NADINE WILL INTERACT WITH THE OTHER SYSTEMS IN THE WESTERLIES THE FORECAST WILL NOT SHOW STRENGTHENING DURING THAT PERIOD. THE NEW FORECAST IS SIMILAR TO...BUT LESS INTENSE THAN...THE PREVIOUS FORECAST USING A BLEND OF THE SHIPS...LGEM...AND INTENSITY CONSENSUS MODELS. FORECAST POSITIONS AND MAX WINDS INIT 13/0900Z 21.5N 51.3W 60 KT 70 MPH 12H 13/1800Z 23.1N 52.7W 65 KT 75 MPH 24H 14/0600Z 25.4N 54.0W 70 KT 80 MPH 36H 14/1800Z 27.6N 54.2W 70 KT 80 MPH 48H 15/0600Z 29.3N 53.3W 65 KT 75 MPH 72H 16/0600Z 31.5N 49.5W 60 KT 70 MPH 96H 17/0600Z 32.5N 44.0W 60 KT 70 MPH 120H 18/0600Z 34.0N 38.0W 60 KT 70 MPH $$ FORECASTER BEVEN |
