Tropical Storm ROSA

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TROPICAL STORM ROSA DISCUSSION NUMBER   5
NWS NATIONAL HURRICANE CENTER MIAMI FL       EP172012
200 AM PDT WED OCT 31 2012
 
RECENT MICROWAVE IMAGES CONTINUE TO SHOW THAT THE LOW-LEVEL CENTER
OF ROSA IS LOCATED ON THE WESTERN EDGE OF THE DEEP CONVECTIVE
MASS.  DVORAK ESTIMATES FROM TAFB AND SAB ARE STEADY FROM 6 HOURS
AGO...AND A PARTIAL ASCAT PASS AT 0434 UTC REVEALED A BAND OF 35-40
KT WINDS WITHIN THE EASTERN SEMICIRCLE.  BASED ON THESE DATA...THE
INTENSITY IS HELD AT 40 KT.  ROSA APPEARS TO HAVE 12 TO 24 HOURS
BEFORE STRONG UPPER-LEVEL WESTERLY WINDS SAG SOUTHWARD CLOSER TO
THE CYCLONE.  THE INTENSITY MODELS INDICATE LITTLE TO NO
STRENGTHENING DURING THAT PERIOD...BUT THE NHC FORECAST LEAVES OPEN
THE POSSIBILITY THAT ROSA COULD GET JUST A BIT STRONGER LATER
TODAY.  EVEN THOUGH THE STORM WILL BE OVER WARM WATERS DURING THE
FORECAST PERIOD...INCREASING VERTICAL SHEAR IN THE NEXT DAY OR TWO
SHOULD CAUSE ROSA TO GRADUALLY WEAKEN AND DEGENERATE INTO A REMNANT
LOW BY DAY 4.

ROSA IS MOVING VERY SLOWLY WESTWARD...OR 275/4 KT.  A MID-LEVEL
ANTICYCLONE LOCATED NEAR 130W APPEARS TO BE IMPEDING THE WESTWARD
MOTION OF ROSA...AND THIS FEATURE IS EXPECTED TO MOVE LITTLE DURING
THE NEXT COUPLE OF DAYS.  ON DAYS 3 THROUGH 5...THE ANTICYCLONE IS
FORECAST TO MIGRATE NORTHWESTWARD WHILE A MID- TO UPPER-LEVEL
CUTOFF LOW DEVELOPS JUST WEST OF THE BAJA PENINSULA.  THIS EVOLVING
PATTERN SHOULD CAUSE ROSA TO DRIFT WESTWARD OR BE NEARLY STATIONARY
OVER THE NEXT 5 DAYS.  THE GFS CONTINUES TO BE THE OUTLIER SOLUTION
BY SHOWING A STRONGER ROSA GETTING PICKED UP BY THE CUTOFF LOW AND
MOVING NORTHEASTWARD BY THE END OF THE FORECAST PERIOD.  HOWEVER...
A BULK OF THE GFS ENSEMBLE MEMBERS SUPPORT THE SLOW WESTWARD MOTION
SHOWN BY THE OTHER DETERMINISTIC MODELS.  PERHAPS IN CELEBRATION OF
HALLOWEEN...THE TRACK GUIDANCE ENVELOPE IS IN THE SHAPE OF A
SQUASHED SPIDER...WHICH IS NORMALLY INDICATIVE OF VERY LITTLE
MOTION.  AS WAS FORESHADOWED IN THE 8 PM PDT DISCUSSION...AN
EASTWARD ADJUSTMENT TO THE PREVIOUS NHC TRACK FORECAST HAS BEEN
MADE...AND THE NEW OFFICIAL FORECAST LIES BETWEEN THE ECMWF MODEL
AND THE MULTI-MODEL CONSENSUS TVCE.
 
FORECAST POSITIONS AND MAX WINDS
 
INIT  31/0900Z 14.5N 117.3W   40 KT  45 MPH
 12H  31/1800Z 14.6N 117.8W   45 KT  50 MPH
 24H  01/0600Z 14.7N 118.3W   40 KT  45 MPH
 36H  01/1800Z 14.7N 118.7W   35 KT  40 MPH
 48H  02/0600Z 14.7N 118.8W   35 KT  40 MPH
 72H  03/0600Z 14.5N 119.5W   30 KT  35 MPH
 96H  04/0600Z 14.5N 120.0W   25 KT  30 MPH...POST-TROP/REMNT LOW
120H  05/0600Z 15.0N 120.5W   20 KT  25 MPH...POST-TROP/REMNT LOW
 
$$
FORECASTER BERG
 
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