[Tropical] Tropical Cyclone Discussion

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WTNT43 KNHC 242041
TCDAT3

HURRICANE RINA DISCUSSION NUMBER   6
NWS NATIONAL HURRICANE CENTER MIAMI FL       AL182011
500 PM EDT MON OCT 24 2011

VISIBLE SATELLITE IMAGES SHOW SEVERAL BANDS OF DEEP CONVECTION
WRAPPING AROUND THE CENTER OF RINA AND A SMALL CENTRAL DENSE
OVERCAST FEATURE. THE HURRICANE HUNTER AIRCRAFT HAS NOT REPORTED
ANY STRONGER WINDS SINCE THEIR INITIAL PASS INTO THE CENTER JUST
BEFORE 1800 UTC...AND BASED ON THE EARLIER DATA THE INITIAL
INTENSITY WILL REMAIN 65 KT.

RINA WILL BE TRAVERSING VERY WARM WATER AND REMAIN IN A LOW SHEAR
ENVIRONMENT DURING THE NEXT COUPLE OF DAYS. THE ONLY NEGATIVE
FACTOR FOR INTENSIFICATION IS AN AREA OF DRY AIR TO THE NORTHWEST
OF THE CYCLONE. SO FAR...RINA HAS REMAINED WELL INSULATED FROM THE
DRY AIR AND THE OFFICIAL FORECAST ASSUMES THAT THE DRY AIR WILL NOT
REACH THE CORE DURING THE NEXT COUPLE OF DAYS. AFTER THAT...
SOUTHERLY SHEAR IS FORECAST TO INCREASE AND RINA IS ALSO EXPECTED
TO INTERACT WITH A FRONTAL BOUNDARY THAT MOVES INTO THE
SOUTHEASTERN GULF OF MEXICO NEAR THE END OF THE FORECAST PERIOD.
THE INTENSITY FORECAST IS VERY SIMILAR TO THE ONE ISSUED IN THE
SPECIAL ADVISORY AND IS NEAR THE GFDL AND HWRF GUIDANCE THROUGH 48
HOURS. AFTER THAT TIME...IT IS CLOSER TO A BLEND OF THE STATISTICAL
AND DYNAMICAL MODEL GUIDANCE. GIVEN THE RELATIVELY SMALL SIZE OF
THE HURRICANE...IT WOULD NOT BE SURPRISING TO SEE RAPID CHANGES
BOTH UP AND DOWN IN ITS INTENSITY.

THE AIRCRAFT FIXES SHOW THAT THE HURRICANE HAS SLOWED DOWN.  A
BUILDING HIGH PRESSURE RIDGE OVER THE NORTHERN GULF OF MEXICO IS
EXPECTED TO STEER RINA WESTWARD DURING THE NEXT 24 TO 36 HOURS.
AS THE RIDGE SLIDES EASTWARD THE HURRICANE SHOULD TURN
NORTHWESTWARD...THEN NORTHWARD IN 2 TO 3 DAYS.  AFTER THAT...THE
TRACK GUIDANCE BECOMES QUITE DIVERGENT WITH THE GFDL AND HWRF
TAKING THE CYCLONE NORTHEASTWARD...AND THE GFS SHOWING AN
EASTWARD OR EAST-SOUTHEASTWARD MOTION.  FOR NOW...THE NHC FORECAST
REMAINS BETWEEN THESE TWO EXTREMES AND SHOWS A SLOW EAST-NORTHEAST
MOTION NEAR THE END OF THE PERIOD.

GIVEN THE EXTREMELY LARGE SPREAD IN THE GUIDANCE...AND THE POOR RUN
TO RUN CONSISTENCY...THERE IS MUCH LOWER THAN NORMAL CONFIDENCE IN
THE LONG-RANGE TRACK FORECAST OF RINA.


FORECAST POSITIONS AND MAX WINDS

INIT  24/2100Z 17.1N  83.1W   65 KT  75 MPH
 12H  25/0600Z 17.2N  83.7W   75 KT  85 MPH
 24H  25/1800Z 17.3N  84.4W   90 KT 105 MPH
 36H  26/0600Z 17.6N  85.2W  100 KT 115 MPH
 48H  26/1800Z 18.1N  86.0W  105 KT 120 MPH
 72H  27/1800Z 19.8N  87.2W   95 KT 110 MPH
 96H  28/1800Z 21.0N  87.0W   85 KT 100 MPH
120H  29/1800Z 21.5N  85.0W   75 KT  85 MPH

$$
FORECASTER BROWN


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