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| #544225 (Received by flhurricane at: 4:50 PM 19.Sep.2012) TCDAT4 TROPICAL STORM NADINE DISCUSSION NUMBER 34 NWS NATIONAL HURRICANE CENTER MIAMI FL AL142012 500 PM AST WED SEP 19 2012 NADINE HAS NOT CHANGED MUCH SINCE EARLIER TODAY...AS IT CONTINUES TO MAINTAIN MINIMAL DEEP CONVECTION...MAINLY TO THE NORTH OF THE CENTER. THE DVORAK TECHNIQUE CONTINUES TO UNDERESTIMATE THE INTENSITY OF THIS MARGINAL TROPICAL CYCLONE...AS THE LATEST CI NUMBERS FROM TAFB AND SAB ONLY SUPPORT 35 KT. AN ASCAT PASS FROM THIS MORNING SHOWED THAT THE MAXIMUM WINDS WERE NEAR 45 KT...AND SINCE THE CONVECTION HAS NOT CHANGED SIGNIFICANTLY FROM THAT TIME...THE ADVISORY WIND SPEED IS KEPT AT THE LATTER VALUE. AMSU ESTIMATES SUGGEST THAT THE CYCLONE MIGHT EVEN BE A LITTLE STRONGER. SINCE NADINE HAS BEEN ABLE TO MAINTAIN ITS INTENSITY WITH SO LITTLE DEEP CONVECTION AND SUBSTANTIAL SHEAR...IT IS PROBABLY DERIVING SOME ENERGY FROM BAROCLINIC SOURCES. THE INTENSITY FORECAST ASSUMES THAT THIS REGIME WILL CONTINUE...SO LITTLE CHANGE IN STRENGTH IS FORECAST FOR THE NEXT SEVERAL DAYS. IT IS PRESUMED THAT WITHIN A DAY OR SO NADINE WILL LOSE MOST OF ITS DEEP CONVECTION AND THEREFORE BECOME A POST-TROPICAL CYCLONE. GLOBAL MODEL FORECASTS SUGGEST THAT THE SYSTEM COULD STRENGTHEN SOMEWHAT AROUND THE END OF THE FORECAST PERIOD. THE CENTER HAS BEEN MEANDERING ABOUT FOR MOST OF THE DAY...AND THE INITIAL MOTION ESTIMATE IS STATIONARY. FORECASTING THE TRACK OF THIS SYSTEM CONTINUES TO BE EXTREMELY CHALLENGING. A PROMINENT BLOCKING PATTERN IS EXPECTED TO EVOLVE AT MID-TROPOSPHERIC LEVELS OVER THE NORTH ATLANTIC...RESULTING IN A COMPLICATED STEERING PATTERN. THE DYNAMICAL TRACK MODELS HAVE HARDLY BEEN A MODEL OF CONSISTENCY FOR NADINE. FOR EXAMPLE...THE 5-DAY FORECAST POSITION FROM THE 1200 UTC RUN OF THE GFS HAS SHIFTED A MERE 900 N MI TO THE SOUTHWEST OF THE 0600 UTC RUN. THE TRACK OF THE CYCLONE IN THE 3- TO 5-DAY RANGE IS APPARENTLY VERY SENSITIVE TO HOW NADINE INTERACTS WITH A STRONG TROUGH OVER THE NORTHEAST ATLANTIC AND A MASSIVE ANTICYCLONE OVER THE NORTH-CENTRAL ATLANTIC. IN ONE SCENARIO...THE SYSTEM IS PULLED EASTWARD BY THE TROUGH... AND IN ANOTHER IT MOVES SOUTHWARD AND WESTWARD ALONG THE SOUTHEASTERN FLANK OF THE ANTICYCLONE. IT IS NOT CLEAR WHICH SCENARIO SHOULD BE FAVORED AT THIS TIME. AS A COURSE OF LEAST REGRET...THE OFFICIAL FORECAST SLOWS THE MOTION TO A CRAWL IN 4 TO 5 DAYS. THIS IS A LITTLE SOUTH OF THE PREVIOUS FORECAST AND NORTH OF THE LATEST MODEL CONSENSUS. FORECAST POSITIONS AND MAX WINDS INIT 19/2100Z 37.1N 32.0W 45 KT 50 MPH 12H 20/0600Z 36.7N 31.2W 45 KT 50 MPH 24H 20/1800Z 35.9N 29.8W 45 KT 50 MPH...POST-TROPICAL 36H 21/0600Z 34.6N 28.1W 45 KT 50 MPH...POST-TROPICAL 48H 21/1800Z 33.5N 26.5W 45 KT 50 MPH...POST-TROPICAL 72H 22/1800Z 33.5N 24.0W 45 KT 50 MPH...POST-TROPICAL 96H 23/1800Z 33.5N 23.0W 45 KT 50 MPH...POST-TROPICAL 120H 24/1800Z 33.5N 22.0W 55 KT 65 MPH...POST-TROPICAL $$ FORECASTER PASCH/ZELINSKY |
