000 WTPZ42 KNHC 010241 TCDEP2 TROPICAL STORM ROSA DISCUSSION NUMBER 8 NWS NATIONAL HURRICANE CENTER MIAMI FL EP172012 800 PM PDT WED OCT 31 2012 A 0145Z SSMIS PASS SHOWS THAT THE CENTER OF ROSA IS STILL DISPLACED TO THE WEST OF THE DEEPEST CONVECTION BY ABOUT 10 KNOTS OF WESTERLY SHEAR. HOWEVER...CLOUD TOPS HAVE COOLED NEAR AND EAST OF THE CENTER OVER THE PAST FEW HOURS AND THE LATEST DVORAK ESTIMATES ARE 3.5/55 KT FROM TAFB AND 3.0/45 KT FROM SAB. BASED ON A BLEND OF THESE... THE INITIAL INTENSITY IS SET TO 50 KT. ROSA SHOULD BE PEAKING IN INTENSITY SOON AS THE SHEAR ALREADY APPEARS TO BE RESTRICTING OUTFLOW IN THE NORTHWEST QUADRANT. THE SHIPS MODEL SHOWS THE SHEAR INCREASING TO OVER 20 KT BY 12 HOURS...WHICH SHOULD RESULT IN GRADUAL WEAKENING. DECAY TO REMNANT LOW STATUS IS FORECAST BY 96 HOURS AS THE SHEAR INCREASES EVEN MORE LATE IN THE PERIOD. THE INITIAL MOTION ESTIMATE IS 260/02. A SLOW WESTWARD OR WEST- SOUTHWESTWARD MOTION SHOULD CONTINUE FOR THE NEXT COUPLE OF DAYS AS ROSA IS SITUATED BETWEEN A MID-LEVEL RIDGE TO THE WEST AND A BROAD FLAT TROUGH PASSING TO THE NORTH. THE SPREAD OF THE TRACK GUIDANCE REMAINS QUITE LARGE AFTER THAT TIME. THE GFS AND HWRF SHOW ROSA MOVING EASTWARD AND THEN TURNING NORTHWARD AS THE CYCLONE COMES UNDER THE INFLUENCE OF A MID-LEVEL LOW THAT FORMS WEST OF BAJA CALIFORNIA. ON THE OTHER SIDE OF THE GUIDANCE ENVELOPE...THE ECMWF SHOWS A NORTHWESTWARD MOTION AT DAYS 4 AND 5 AS ROSA INTERACTS WITH A WEAKER POSITIVELY-TILTED TROUGH...ENDING UP ABOUT 500 MILES SOUTHWEST OF THE GFS AT DAY 5. GIVEN THAT THE GFS/HWRF SOLUTION STILL APPEARS TO BE AN OUTLIER COMPARED TO THE GEFS AND ECMWF ENSEMBLE MEMBERS...THE NHC FORECAST CONTINUES TO FAVOR THE MORE WESTWARD SOLUTION. THE NEW NHC TRACK LIES ROUGHLY BETWEEN...BUT IS A BIT SLOWER THAN...A BLEND OF THE ECMWF AND THE GEFS ENSEMBLE MEAN AT DAYS 4 AND 5. NEEDLESS TO SAY...CONFIDENCE IN THE TRACK FORECAST IS LOWER THAN NORMAL LATE IN THE PERIOD. FORECAST POSITIONS AND MAX WINDS INIT 01/0300Z 14.1N 118.1W 50 KT 60 MPH 12H 01/1200Z 14.1N 118.4W 45 KT 50 MPH 24H 02/0000Z 14.1N 118.6W 40 KT 45 MPH 36H 02/1200Z 14.0N 118.8W 35 KT 40 MPH 48H 03/0000Z 13.9N 119.0W 35 KT 40 MPH 72H 04/0000Z 14.0N 119.5W 30 KT 35 MPH 96H 05/0000Z 14.5N 120.5W 25 KT 30 MPH...POST-TROP/REMNT LOW 120H 06/0000Z 16.0N 122.0W 25 KT 30 MPH...POST-TROP/REMNT LOW $$ FORECASTER BRENNAN