000 WTNT43 KNHC 271445 TCDAT3 TROPICAL STORM RINA DISCUSSION NUMBER 18 NWS NATIONAL HURRICANE CENTER MIAMI FL AL182011 1000 AM CDT THU OCT 27 2011 A COMBINATION OF SOUTHERLY VERTICAL WIND SHEAR AND MID/UPPER-LEVEL DRY AIR ENTRAINMENT APPEARS TO HAVE DISRUPTED THE CONVECTIVE STRUCTURE OF RINA. THE LOW-LEVEL CENTER IS NOW PARTIALLY EXPOSED AT THE SOUTHERN EDGE OF A BURST OF DEEP CONVECTION...AND RADAR DATA FROM BELIZE CITY AND CANCUN SHOWS LITTLE EVIDENCE OF BANDING IN THE CONVECTION. A NOAA HURRICANE HUNTER AIRCRAFT INVESTIGATING THE STORM IS REPORTING FLIGHT-LEVEL WINDS BELOW HURRICANE STRENGTH AND SURFACE WIND ESTIMATES FROM THE STEPPED FREQUENCY MICROWAVE RADIOMETER NEAR 60 KT. BASED ON THESE DATA...RINA IS DOWNGRADED TO A 60 KT TROPICAL STORM. AFTER WOBBLING A LITTLE MORE WESTWARD...RINA APPEARS TO HAVE RESUMED ITS RIGHT TURN WITH THE INITIAL MOTION NOW 330/5. RINA SHOULD MOVE SLOWLY NORTHWARD NEAR THE EAST COAST OF THE YUCATAN PENINSULA FOR THE NEXT 24-36 HOURS ON THE WEST SIDE OF A MID/UPPER-LEVEL RIDGE OVER THE CARIBBEAN SEA. AFTER THAT...THE DYNAMICAL MODELS ARE IN GOOD AGREEMENT THAT A COMBINATION OF RINA WEAKENING TO A SHALLOW VORTEX AND RISING LOW-LEVEL PRESSURES TO ITS NORTHWEST SHOULD CAUSE RINA TO TURN SOUTHWARD. WHILE THERE ARE DIFFERENCE IN THE DETAILS...THE GUIDANCE SUGGESTS THAT RINA OR ITS REMNANTS WILL MEANDER OVER THE NORTHWEST CARIBBEAN SEA OR THE YUCATAN PENINSULA FOR THE REST OF THE FORECAST PERIOD. THE NEW FORECAST TRACK SHOWS A SHARPER TURN AND A SLIGHTLY FASTER SOUTHWARD MOTION THAN THE PREVIOUS FORECAST. HOWEVER...IN DEFERENCE TO THE PREVIOUS FORECAST...IT DOES NOT SHOW AS FAST OF A SOUTHWARD MOTION AS MOST OF THE DYNAMICAL MODELS. MODERATE TO STRONG SOUTHERLY VERTICAL WIND SHEAR IS LIKELY TO PERSIST NEAR OR OVER RINA FOR THE NEXT 96 HOURS OR SO. THIS... ALONG WITH ADDITIONAL DRY AIR ENTRAINING INTO THE CYCLONE...SHOULD CAUSE CONTINUED WEAKENING. THE NEW INTENSITY FORECAST CALLS FOR A FASTER WEAKENING THAN PREVIOUS...WITH RINA WEAKENING TO A TROPICAL DEPRESSION IN ABOUT 72 HOURS AND DEGENERATING TO A REMNANT LOW BY 120 HOURS. SINCE THE ENVIRONMENT IS HOSTILE AND THE CYCLONE IS RELATIVELY SMALL...THIS DEGENERATION COULD OCCUR EARLIER THAN FORECAST...ESPECIALLY IF THE CENTER MOVES BACK OVER THE YUCATAN PENINSULA. FORECAST POSITIONS AND MAX WINDS INIT 27/1500Z 19.2N 87.0W 60 KT 70 MPH 12H 28/0000Z 20.0N 87.1W 55 KT 65 MPH 24H 28/1200Z 21.1N 87.1W 50 KT 60 MPH...INLAND 36H 29/0000Z 21.6N 86.7W 45 KT 50 MPH...OVER WATER 48H 29/1200Z 21.4N 86.2W 40 KT 45 MPH 72H 30/1200Z 21.0N 86.0W 30 KT 35 MPH 96H 31/1200Z 20.0N 86.0W 25 KT 30 MPH 120H 01/1200Z 19.0N 86.0W 20 KT 25 MPH...POST-TROP/REMNT LOW $$ FORECASTER BEVEN