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Tropical Storm ROSA


ZCZC MIATCDEP2 ALL
TTAA00 KNHC DDHHMM
 
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
 
NNNN


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Page last modified: Monday, 31-Dec-2012 12:10:45 UTC