341 
 WTNT43 KNHC 280836
 TCDAT3
  
 TROPICAL STORM RINA DISCUSSION NUMBER  21
 NWS NATIONAL HURRICANE CENTER MIAMI FL       AL182011
 400 AM CDT FRI OCT 28 2011
  
 AFTER AN EARLIER BURST OF VERY COLD-TOPPED CONVECTION OVER THE
 LOW-LEVEL CENTER...WATER VAPOR IMAGERY INDICATES A SURGE OF 40-KT
 SOUTHERLY UPPER-LEVEL WINDS HAS STARTED TO SHEAR AWAY THE
 CONVECTION. AS A RESULT OF THE SHARP DEGRADATION IN THE CONVECTIVE
 STRUCTURE...THE INITIAL INTENSITY HAS BEEN DECREASED TO 45 KT...
 WHICH IS CONSISTENT WITH THE DOWNWARD TREND IN WIND SPEEDS NOTED IN
 NEARBY SURFACE OBSERVATION SITES. 
  
 THE INITIAL POSITION IS BASED ON A COUPLE OF SURFACE OBS AND POOR
 RADAR SIGNATURES FROM BOTH CUBAN AND MEXICAN RADARS...WHICH MAKES
 THE INITIAL MOTION ESTIMATE AN UNCERTAIN 015/04 KT. THE RAGGED
 APPEARANCE IN RADAR IMAGERY SUGGESTS THAT THE SMALL CIRCULATION OF
 RINA MAY ALREADY BE SUCCUMBING TO THE INCREASING SOUTHERLY VERTICAL
 WIND SHEAR. SOME MID-LEVEL ROTATION HAS BECOME APPARENT JUST
 NORTHEAST OF THE TIP OF YUCATAN...WHEREAS SURFACE OBS INDICATE THE
 SURFACE CENTER IS STILL OVER LAND. WITH THE VERTICAL CIRCULATIONS
 FORECAST TO COMPLETELY DECOUPLE DURING THE NEXT 12 HOURS OR SO...
 THE LOW-LEVEL CENTER IS EXPECTED TO GRADUALLY TURN SLOWLY EASTWARD
 AND THEN TURN SOUTHWARD BACK OVER THE NORTHWESTERN CARIBBEAN SEA BY
 24 HOURS. THE OFFICIAL FORECAST TRACK IS SIMILAR TO THE PREVIOUS
 ADVISORY AND IS WELL TO THE RIGHT OF THE CONSENSUS MODELS...TVCN
 AND TVCA.
 
 SINCE THE VERTICAL SHEAR IS FORECAST TO GRADUALLY INCREASE...THE
 MID-/UPPER-LEVEL CIRCULATION IS EXPECTED TO DECOUPLE FROM THE
 LOW-LEVEL CIRCULATION AND LIFT OUT TO THE NORTHEAST WHILE THE
 LOW-LEVEL CIRCULATION REMAINS BEHIND OVER THE NORTHWESTERN
 CARIBBEAN SEA. THIS STRONG SHEAR PATTERN SHOULD CAUSE RINA TO
 STEADILY WEAKEN THROUGHOUT THE FORECAST PERIOD...AND THE CYCLONE
 COULD BECOME A TROPICAL DEPRESSION BY LATER TODAY OR EARLY
 SATURDAY. RINA IS EXPECTED TO BECOME A REMNANT LOW OVER THE
 NORTHWESTERN CARIBBEAN BY 48 HOURS...BUT WITH A SLIGHT CHANCE OF
 REGENERATING INTO A TROPICAL CYCLONE IF IT DOES NOT GET ABSORBED
 INTO THE BROAD LOW PRESSURE SYSTEM LOCATED EAST OF NICARAGUA.
  
 FORECAST POSITIONS AND MAX WINDS
  
 INIT  28/0900Z 21.1N  87.0W   45 KT  50 MPH
  12H  28/1800Z 21.5N  86.8W   40 KT  45 MPH
  24H  29/0600Z 21.3N  86.4W   35 KT  40 MPH
  36H  29/1800Z 20.6N  86.1W   30 KT  35 MPH
  48H  30/0600Z 20.0N  86.1W   25 KT  30 MPH...POST-TROP/REMNT LOW
  72H  31/0600Z 19.2N  86.3W   25 KT  30 MPH...POST-TROP/REMNT LOW
  96H  01/0600Z 17.9N  86.8W   20 KT  25 MPH...POST-TROP/REMNT LOW
 120H  02/0600Z 17.0N  87.1W   20 KT  25 MPH...POST-TROP/REMNT LOW
  
 $$
 FORECASTER STEWART