000
WTPZ42 KNHC 311440
TCDEP2
 
TROPICAL STORM ROSA DISCUSSION NUMBER   6
NWS NATIONAL HURRICANE CENTER MIAMI FL       EP172012
800 AM PDT WED OCT 31 2012
 
DEEP CONVECTION HAS BEEN ON THE INCREASE NEAR THE CENTER OF ROSA
WITH A BIT MORE CURVATURE SEEN IN THE OVERALL CLOUD PATTERN. AN
OSCAT PASS FROM OVERNIGHT SHOWED THAT THE CENTER WAS MORE EMBEDDED
WITHIN THE CENTRAL CONVECTION...WHICH SUGGESTS THE STORM IS
PROBABLY A LITTLE STRONGER. THE WIND SPEED IS SET TO 45 KT...
CONSISTENT WITH THE MOST RECENT SAB SATELLITE CLASSIFICATION. ROSA
HAS ABOUT 24 HOURS BEFORE WESTERLY SHEAR IS LIKELY TO HALT ANY
INTENSIFICATION. MOST OF THE GUIDANCE SHOW NO SIGNIFICANT CHANGE IN
STRENGTH FOR THE NEXT DAY OR SO...WITH A STEADY WEAKENING AFTER
THAT TIME. THE OFFICIAL FORECAST IS CLOSE TO THE TREND OF THE
PREVIOUS ONE WITH A BLEND OF THE LATEST INTENSITY CONSENSUS AID.
STRONG VERTICAL SHEAR SHOULD CAUSE ROSA TO DEGENERATE INTO A
REMNANT LOW BY DAY 4.

ROSA APPEARS TO BE MOVING VERY SLOWLY WESTWARD...OR 275/3. THE STORM
IS WITHIN AN AREA OF RELATIVELY LIGHT STEERING DUE TO A MID-LEVEL
ANTICYCLONE LOCATED NEAR 130W AND A FLAT TROUGH OVER MEXICO. LITTLE
CHANGE TO THIS PATTERN IS INDICATED BY MOST OF THE MODELS FOR THE
NEXT COUPLE OF DAYS...SO THE NHC FORECAST WILL JUST CONTINUE THE
SLOW WESTWARD MOTION. IN THE LONG RANGE...A CUT-OFF LOW IS EXPECTED
TO FORM JUST TO THE WEST OF THE BAJA PENINSULA AND DROP
SOUTHWESTWARD WHILE THE ANTICYCLONE WEAKENS. THERE CONTINUE TO BE
LARGE DIFFERENCES IN THE MODELS WITH THE TIMING OF THIS LOW...WITH
THE GLOBAL MODELS TOTALLY AT ODDS WITH THE FORECAST MOTION BEYOND A
DAY OR TWO. THE GFS MODEL HAS A MUCH STRONGER LOW THAN MOST OF THE
OTHER GUIDANCE...AND CONSEQUENTLY TURNS ROSA TO THE NORTHEAST AHEAD
OF THE LOW. THE GFS ENSEMBLE MEMBERS SUGGEST THAT THE GFS
DETERMINISTIC FORECAST IS SOMEWHAT OF AN OUTLIER...WITH THE MAJORITY
OF THE ENSEMBLE MEMBERS CLOSER TO THE MORE WESTWARD ECMWF OR HWRF
MODEL SOLUTIONS. GIVEN THE HIGH UNCERTAINTY...THE OFFICIAL FORECAST
WILL STAY CLOSE TO THE PREVIOUS NHC PREDICTION...REMAINING WEST OF
THE MODEL CONSENSUS.
 
FORECAST POSITIONS AND MAX WINDS
 
INIT  31/1500Z 14.5N 117.6W   45 KT  50 MPH
 12H  01/0000Z 14.6N 117.9W   45 KT  50 MPH
 24H  01/1200Z 14.7N 118.3W   45 KT  50 MPH
 36H  02/0000Z 14.7N 118.7W   40 KT  45 MPH
 48H  02/1200Z 14.6N 118.9W   35 KT  40 MPH
 72H  03/1200Z 14.4N 119.7W   30 KT  35 MPH
 96H  04/1200Z 14.5N 120.3W   30 KT  35 MPH...POST-TROP/REMNT LOW
120H  05/1200Z 15.5N 121.0W   25 KT  30 MPH...POST-TROP/REMNT LOW
 
$$
FORECASTER BLAKE