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| #546020 (Received by flhurricane at: 4:35 PM 27.Sep.2012) TCDAT4 TROPICAL STORM NADINE DISCUSSION NUMBER 61 NWS NATIONAL HURRICANE CENTER MIAMI FL AL142012 500 PM AST THU SEP 27 2012 THE CONVECTION ASSOCIATED WITH NADINE HAS CHANGED FROM RAGGED TO WRAPPED-UP THIS AFTERNOON...WITH FORMATION OF A WELL-DEFINED CENTRAL DENSE OVERCAST AND AN EARLIER ATTEMPT AT EYE FORMATION. SATELLITE INTENSITY ESTIMATES FROM TAFB AND SAB HAVE INCREASED TO 55 KT...AND THAT IS THE INITIAL INTENSITY. THIS COULD BE A LITTLE CONSERVATIVE...AS RECENT AMSU INTENSITY ESTIMATES FROM CIMSS AND CIRA HAVE BEEN 55-65 KT. THE CIRRUS OUTFLOW IS FAIR IN THE NORTHEASTERN SEMICIRCLE...BUT IT IS RESTRICTED IN THE SOUTHWESTERN SEMICIRCLE WHERE THERE ARE SIGNS OF INCREASING VERTICAL WIND SHEAR. THE INITIAL MOTION IS NOW 255/6. NADINE IS ON THE SOUTH SIDE OF A DEEP-LAYER RIDGE...WHICH IS FORECAST TO MOVE EASTWARD DURING THE NEXT 48-72 HR. THIS WILL ALLOW NADINE TO TURN NORTHWESTWARD AND NORTHWARD AS IT MOVES BETWEEN THE RIDGE AND A MID/UPPER-LEVEL LOW SEEN IN WATER VAPOR IMAGERY NEAR 30N48W. AFTER 72 HR...THE TRACK GUIDANCE REMAINS CONSISTENT IN ITS DIVERGENCE. THE GFS...GFS ENSEMBLE MEAN...GFDL...AND HWRF FORECAST NADINE TO MOVE SLOWLY EASTWARD TO NORTHEASTWARD ALONG THE SOUTHERN EDGE OF THE WESTERLIES AS A TROUGH PASSES NORTH OF THE STORM. THE UKMET...ECMWF... CANADIAN...AND NOGAPS FORECAST A RIDGE TO BUILD NORTH AND NORTHWEST OF NADINE IN THE WAKE OF THE WESTERLY TROUGH...WHICH WOULD STEER THE STORM BACK TOWARD THE SOUTH OR SOUTHWEST. SINCE THERE IS LITTLE CHANGE TO THE TRACK GUIDANCE SINCE THE LAST ADVISORY...THE NEW FORECAST TRACK IS AN UPDATE OF THE PREVIOUS FORECAST...WITH A FORECAST SLOW MOTION AFTER 72 HR. THE GLOBAL MODELS FORECAST NADINE TO INTERACT WITH THE MID/UPPER-LEVEL LOW NEAR 30N48W DURING THE FORECAST PERIOD...WITH THE TWO SYSTEMS POSSIBLY MERGING BY 96-120 HR. IN ADDITION...SMALL SHORTWAVE TROUGHS ROTATING AROUND THE LOW COULD ALSO INTERACT WITH THE STORM. WHILE IT IS EXPECTED THAT NADINE WILL ENCOUNTER INCREASING SHEAR...IT IS POSSIBLE THAT THE SHORTWAVE TROUGHS COULD PARTLY SHIELD THE STORM...AS WELL AS PROVIDE UPPER-LEVEL DIVERGENCE THAT COULD ALLOW STRENGTHENING. THE INTENSITY GUIDANCE IS IN FAIR AGREEMENT ON FORECASTING A LITTLE MORE INTENSIFICATION BEFORE NADINE REACHES COOLER SEA SURFACE TEMPERATURES IN ABOUT 36 HR. THE NEW INTENSITY FORECAST DOES LIKEWISE AND IS NOW CLOSE TO THE SHIPS...LGEM...AND INTENSITY CONSENSUS MODELS. HOWEVER...THIS IS A LOW CONFIDENCE FORECAST DUE TO THE UNCERTAINTY IN HOW MUCH SHEAR NADINE COULD ENCOUNTER. FORECAST POSITIONS AND MAX WINDS INIT 27/2100Z 28.6N 32.8W 55 KT 65 MPH 12H 28/0600Z 28.8N 33.8W 60 KT 70 MPH 24H 28/1800Z 29.7N 34.8W 60 KT 70 MPH 36H 29/0600Z 31.2N 35.5W 60 KT 70 MPH 48H 29/1800Z 32.9N 36.1W 60 KT 70 MPH 72H 30/1800Z 35.5N 37.0W 55 KT 65 MPH 96H 01/1800Z 36.0N 37.0W 50 KT 60 MPH 120H 02/1800Z 36.5N 37.0W 45 KT 50 MPH $$ FORECASTER BEVEN |
