000 WTPZ42 KNHC 310237 TCDEP2 TROPICAL STORM ROSA DISCUSSION NUMBER 4 NWS NATIONAL HURRICANE CENTER MIAMI FL EP172012 800 PM PDT TUE OCT 30 2012 SATELLITE IMAGERY SHOWS THAT THE CONVECTIVE PATTERN OF ROSA HAS NOT CHANGED MUCH OVER THE PAST FEW HOURS. THE COLDEST CLOUD TOPS ARE SEEN IN A CDO-LIKE FEATURE EAST OF THE LOW-LEVEL CENTER...WHILE THERE IS LITTLE CONVECTIVE BANDING ELSEWHERE. DVORAK ESTIMATES REMAIN 45 KT FROM SAB AND 35 KT FROM TAFB...AND THE INITIAL INTENSITY REMAINS 40 KT BASED ON A BLEND OF THESE VALUES. WESTERLY FLOW ALOFT TO THE NORTH OF ROSA APPEARS TO BE ENHANCING THE OUTFLOW IN THAT SEMICIRCLE...BUT THE SHEAR IS DISPLACING THE CONVECTION EAST OF THE LOW-LEVEL CENTER. GLOBAL MODEL FIELDS AND THE SHIPS GUIDANCE SHOW WESTERLY SHEAR INCREASING OVER THE NEXT 24 HOURS... WHICH SHOULD ALLOW FOR ONLY LIMITED STRENGTHENING IN THE SHORT TERM. AFTER 24 HOURS...A CONTINUED INCREASE IN SHEAR SHOULD LEAD TO WEAKENING AND REMNANT LOW STATUS IN ABOUT 4 DAYS. A 2231 UTC AMSU PASS SHOWED THAT ROSA IS LOCATED A LITTLE TO THE EAST OF EARLIER ESTIMATES...AND THE INITIAL MOTION ESTIMATE IS 275/04. ROSA IS CURRENTLY SITUATED ON THE SOUTHEASTERN FLANK OF A MID-LEVEL RIDGE....WHICH SHOULD RESULT IN A SLOW WESTWARD MOTION FOR THE NEXT DAY OR SO. THEN...AS A DEEP-LAYER TROUGH MOVES INTO THE EASTERN PACIFIC TO THE NORTH OF THE TROPICAL CYCLONE...THE TRACK MODEL GUIDANCE BECOMES QUITE DIVERGENT. THE ECMWF...UKMET... AND NOGAPS SHOW A WEAKENING ROSA TURNING WEST-SOUTHWESTWARD BY DAY 4. ALTERNATIVELY...THE GFS AND GFDL SHOW A DEEPER REPRESENTATION OF ROSA TURNING NORTHEASTWARD AT DAYS 4 AND 5 IN RESPONSE TO A MID- LEVEL CUTOFF LOW THAT FORMS OFF THE COAST OF THE BAJA PENINSULA. GIVEN THAT ROSA IS NOT EXPECTED TO BE IN AN ENVIRONMENT CONDUCIVE FOR MUCH STRENGTHENING...THE GFS/GFDL SEENARIO SEEMS A LITTLE LESS LIKELY...ALTHOUGH THIS SOLUTION NOW HAS THE SUPPORT OF A FEW OF THE GEFS ENSEMBLE MEMBERS. GIVEN THAT THE TVCE MULTI-MODEL CONSENSUS AND THE GEFS ENSEMBLE MEAN SHOW VERY LITTLE MOTION AT DAYS 3 THROUGH 5...THE NHC FORECAST HAS BEEN SLOWED DOWN CONSIDERABLY...BUT STILL SHOWS A WEST-SOUTHWESTWARD MOTION TO PROVIDE SOME CONTINUITY WITH THE PREVIOUS NHC FORECAST. FURTHER ADJUSTMENTS TO THE TRACK MAY BE NECESSARY IN THE NEXT CYCLE. FORECAST POSITIONS AND MAX WINDS INIT 31/0300Z 14.5N 117.0W 40 KT 45 MPH 12H 31/1200Z 14.6N 117.6W 45 KT 50 MPH 24H 01/0000Z 14.7N 118.3W 45 KT 50 MPH 36H 01/1200Z 14.8N 118.8W 40 KT 45 MPH 48H 02/0000Z 14.9N 119.3W 40 KT 45 MPH 72H 03/0000Z 14.5N 120.5W 35 KT 40 MPH 96H 04/0000Z 14.2N 121.7W 30 KT 35 MPH...POST-TROP/REMNT LOW 120H 05/0000Z 14.0N 123.0W 25 KT 30 MPH...POST-TROP/REMNT LOW $$ FORECASTER BRENNAN