[Tropical] Tropical Cyclone Discussion

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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



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