000 WTPZ42 KNHC 302040 TCDEP2 TROPICAL STORM ROSA DISCUSSION NUMBER 3 NWS NATIONAL HURRICANE CENTER MIAMI FL EP172012 200 PM PDT TUE OCT 30 2012 ROSA CONTINUES TO SLOWLY ORGANIZE. VISIBLE IMAGERY SHOWS THAT WHILE CONVECTION HAS WEAKENED SOMEWHAT NEAR THE CENTER...A WELL-DEFINED CURVED BAND HAS FORMED IN THE SOUTHERN SEMICIRCLE. SATELLITE INTENSITY ESTIMATES ARE 35 KT AND 45 KT FROM TAFB AND SAB RESPECTIVELY...SO A BLEND OF 40 KT IS USED FOR THE INITIAL WIND SPEED. THE CENTER OF ROSA REMAINS ON THE WEST SIDE OF THE DEEP CONVECTION...A SIGN OF THE WESTERLY SHEAR. MOST OF THE LARGE-SCALE MODELS SUGGEST ROSA WILL STAY JUST SOUTH OF A BAND OF STRONG SHEAR FOR THE NEXT DAY OR SO. THEREAFTER...THE MAJORITY OF THE GUIDANCE SHOWS INCREASING WESTERLY SHEAR DUE TO AN UPPER-LEVEL TROUGH DIGGING OVER THE EASTERN PACIFIC. THE INTENSITY MODELS NOW SHOW THE STORM GETTING A LITTLE STRONGER BEFORE THE SHEAR ARRIVES...SO THE OFFICIAL WIND SPEED FORECAST FOLLOWS THAT TREND. VISIBLE AND MICROWAVE DATA GIVE A MORE CERTAIN MOTION ESTIMATE OF 280/5...A BIT SLOWER AND WEST OF PREVIOUS ESTIMATES. A WEAK RIDGE OVER THE EASTERN PACIFIC SHOULD STEER THE STORM SLOWLY WESTWARD THROUGH WEDNESDAY. HOWEVER...THE TRACK FORECAST IS CONSIDERABLY MORE UNCERTAIN AFTER THAT TIME...WITH DIFFERENCES IN BOTH THE DEPTH OF THE TROPICAL CYCLONE AND THE MID-LEVEL PATTERN BECOMING APPARENT. THE GFS MODEL HAS JOINED THE GFDL SOLUTION OF A DEEPER STORM...WHICH FEELS THE EFFECT OF WESTERLY WINDS ALOFT AND CAUSES ROSA TO SLOW DOWN OR EVEN TURN NORTHEASTWARD BY DAY 5. SINCE THE GFS FORECAST MADE SUCH A LARGE CHANGE AND IS AT ODDS WITH ITS MORE WESTWARD ENSEMBLE MEAN PREDICTION...THE OFFICIAL FORECAST WILL STAY CLOSER TO THE PREVIOUS FORECAST AND NEAR A BLEND OF THE ECMWF/GFS ENSEMBLE MEAN. THE FORECAST WAS ADJUSTED SOUTHEASTWARD BY A FAIR AMOUNT...BUT IS WELL WEST OF THE MODEL CONSENSUS. FORECAST POSITIONS AND MAX WINDS INIT 30/2100Z 14.4N 116.7W 40 KT 45 MPH 12H 31/0600Z 14.6N 117.5W 45 KT 50 MPH 24H 31/1800Z 14.9N 118.4W 50 KT 60 MPH 36H 01/0600Z 15.0N 119.1W 45 KT 50 MPH 48H 01/1800Z 15.0N 119.7W 40 KT 45 MPH 72H 02/1800Z 14.5N 120.8W 35 KT 40 MPH 96H 03/1800Z 13.5N 122.5W 30 KT 35 MPH...POST-TROP/REMNT LOW 120H 04/1800Z 13.5N 124.5W 25 KT 30 MPH...POST-TROP/REMNT LOW $$ FORECASTER BLAKE