ZCZC MIATCDEP2 ALL TTAA00 KNHC DDHHMM TROPICAL STORM ROSA DISCUSSION NUMBER 7 NWS NATIONAL HURRICANE CENTER MIAMI FL EP172012 200 PM PDT WED OCT 31 2012 VISIBLE SATELLITE IMAGES AND MICROWAVE DATA SHOW THAT THE CENTER OF ROSA REMAINS ON THE WESTERN EDGE OF A LARGE AREA OF DEEP CONVECTION. SATELLITE INTENSITY ESTIMATES ARE 45 KT FROM TAFB AND SAB...WITH A RECENT ASCAT PASS SHOWING MAXIMUM WINDS OF ABOUT 40 KT. THUS THE INITIAL INTENSITY REMAINS 45 KT. WESTERLY VERTICAL WIND SHEAR IS EXPECTED TO SIGNIFICANTLY INCREASE TOMORROW...WHICH SHOULD INDUCE WEAKENING. THIS SCENARIO HAS BEEN WELL ADVERTISED BY THE LARGE-SCALE AND REGIONAL GUIDANCE...AND THE LATEST NHC FORECAST IS BASICALLY AN UPDATE OF THE PREVIOUS ONE. STRONG VERTICAL SHEAR STILL SHOULD CAUSE ROSA TO DEGENERATE INTO A REMNANT LOW BY DAY 4. THE INITIAL MOTION OF ROSA IS ESTIMATED TO BE ABOUT 260/3...WITH THE ASCAT AND OTHER MICROWAVE DATA SHOWING PRETTY CLEARLY THAT THE STORM HAS BEEN MOVING A BIT SOUTH OF WEST TODAY. THE TROPICAL CYCLONE REMAINS CAUGHT WITHIN LIGHT STEERING BETWEEN A MID-LEVEL HIGH LOCATED NEAR 130W AND FLAT TROUGHING NORTH OF ROSA. OTHER THAN ACCOUNTING FOR A SLIGHT SOUTHWARD RELOCATION OF THE CENTER...THE FORECAST TRACK OF ROSA IS BASICALLY UNCHANGED DURING THE NEXT DAY OR SO. THE MODEL GUIDANCE FROM THIS CYCLE IS EERILY SIMILAR TO THE PREVIOUS PACKAGE WITH A HUGE DISPARITY BETWEEN THE BEST PERFORMING MODELS. THE KEY TO THE FORECAST COULD LIE IN THE EVOLUTION OF A SIGNIFICANT CUTOFF LOW THAT IS PREDICTED BY MOST OF THE GUIDANCE TO FORM WEST OF BAJA CALIFORNIA IN A FEW DAYS. THE MODELS THAT FORM A STRONGER LOW FASTER...SUCH AS THE GFS/GFDL/HWRF...SHOW ROSA TURNING TOWARD THE NORTH BEYOND DAY 3 AS IT GETS CAUGHT BY THE TROUGH. HOWEVER...ANOTHER CAMP OF MODELS...INCLUDING THE ECMWF/UKMET/GEFS MEAN AND FSU SUPERENSEMBLE...SHOW A SLOWER AND MORE POSITIVELY TILTED TROUGH...WHICH CAUSES ROSA TO SHEAR OUT SOONER AND CONTINUE MOVING WESTWARD. THE GEFS AND ECMWF ENSEMBLE MEMBERS SUPPORT THE WESTWARD MODEL SOLUTIONS...AND THE OFFICIAL FORECAST CONTINUES TO LEAN IN THAT DIRECTION. FORECAST POSITIONS AND MAX WINDS INIT 31/2100Z 14.2N 117.9W 45 KT 50 MPH 12H 01/0600Z 14.3N 118.2W 45 KT 50 MPH 24H 01/1800Z 14.3N 118.6W 40 KT 45 MPH 36H 02/0600Z 14.2N 118.8W 35 KT 40 MPH 48H 02/1800Z 14.0N 119.0W 35 KT 40 MPH 72H 03/1800Z 13.8N 119.6W 30 KT 35 MPH 96H 04/1800Z 14.5N 120.5W 30 KT 35 MPH...POST-TROP/REMNT LOW 120H 05/1800Z 15.5N 121.0W 25 KT 30 MPH...POST-TROP/REMNT LOW $$ FORECASTER BLAKE NNNN
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Page last modified: Monday, 31-Dec-2012 12:10:45 UTC