Tropical Storm ROSA

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TROPICAL STORM ROSA DISCUSSION NUMBER   3
NWS NATIONAL HURRICANE CENTER MIAMI FL       EP172012
200 PM PDT TUE OCT 30 2012
 
ROSA CONTINUES TO SLOWLY ORGANIZE. VISIBLE IMAGERY SHOWS THAT WHILE
CONVECTION HAS WEAKENED SOMEWHAT NEAR THE CENTER...A WELL-DEFINED
CURVED BAND HAS FORMED IN THE SOUTHERN SEMICIRCLE. SATELLITE
INTENSITY ESTIMATES ARE 35 KT AND 45 KT FROM TAFB AND SAB
RESPECTIVELY...SO A BLEND OF 40 KT IS USED FOR THE INITIAL WIND
SPEED.

THE CENTER OF ROSA REMAINS ON THE WEST SIDE OF THE DEEP
CONVECTION...A SIGN OF THE WESTERLY SHEAR. MOST OF THE LARGE-SCALE
MODELS SUGGEST ROSA WILL STAY JUST SOUTH OF A BAND OF STRONG SHEAR
FOR THE NEXT DAY OR SO. THEREAFTER...THE MAJORITY OF THE GUIDANCE
SHOWS INCREASING WESTERLY SHEAR DUE TO AN UPPER-LEVEL TROUGH
DIGGING OVER THE EASTERN PACIFIC. THE INTENSITY MODELS NOW SHOW THE
STORM GETTING A LITTLE STRONGER BEFORE THE SHEAR ARRIVES...SO THE
OFFICIAL WIND SPEED FORECAST FOLLOWS THAT TREND.

VISIBLE AND MICROWAVE DATA GIVE A MORE CERTAIN MOTION ESTIMATE OF
280/5...A BIT SLOWER AND WEST OF PREVIOUS ESTIMATES. A WEAK RIDGE
OVER THE EASTERN PACIFIC SHOULD STEER THE STORM SLOWLY WESTWARD
THROUGH WEDNESDAY. HOWEVER...THE TRACK FORECAST IS CONSIDERABLY
MORE UNCERTAIN AFTER THAT TIME...WITH DIFFERENCES IN BOTH THE DEPTH
OF THE TROPICAL CYCLONE AND THE MID-LEVEL PATTERN BECOMING
APPARENT. THE GFS MODEL HAS JOINED THE GFDL SOLUTION OF A DEEPER
STORM...WHICH FEELS THE EFFECT OF WESTERLY WINDS ALOFT AND CAUSES
ROSA TO SLOW DOWN OR EVEN TURN NORTHEASTWARD BY DAY 5. SINCE THE
GFS FORECAST MADE SUCH A LARGE CHANGE AND IS AT ODDS WITH ITS MORE
WESTWARD ENSEMBLE MEAN PREDICTION...THE OFFICIAL FORECAST WILL STAY
CLOSER TO THE PREVIOUS FORECAST AND NEAR A BLEND OF THE ECMWF/GFS
ENSEMBLE MEAN. THE FORECAST WAS ADJUSTED SOUTHEASTWARD BY A FAIR
AMOUNT...BUT IS WELL WEST OF THE MODEL CONSENSUS.
 
FORECAST POSITIONS AND MAX WINDS
 
INIT  30/2100Z 14.4N 116.7W   40 KT  45 MPH
 12H  31/0600Z 14.6N 117.5W   45 KT  50 MPH
 24H  31/1800Z 14.9N 118.4W   50 KT  60 MPH
 36H  01/0600Z 15.0N 119.1W   45 KT  50 MPH
 48H  01/1800Z 15.0N 119.7W   40 KT  45 MPH
 72H  02/1800Z 14.5N 120.8W   35 KT  40 MPH
 96H  03/1800Z 13.5N 122.5W   30 KT  35 MPH...POST-TROP/REMNT LOW
120H  04/1800Z 13.5N 124.5W   25 KT  30 MPH...POST-TROP/REMNT LOW
 
$$
FORECASTER BLAKE
 
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