[Tropical] Tropical Cyclone Discussion

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WTNT41 KNHC 180253
TCDAT1
TROPICAL STORM FAY DISCUSSION NUMBER  10
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL   AL062008
1100 PM EDT SUN AUG 17 2008

AIR FORCE RECONNAISSANCE REPORTS NEAR 0000 UTC SHOWED LITTLE MOTION
SINCE THE EARLIER FIXES.  RECENT SATELLITE IMAGERY AND CUBAN RADAR
DATA IMAGERY INDICATE THAT THE CENTER IS ILL-DEFINED AT THE
MOMENT...AND SURFACE SYNOPTIC DATA SUGGEST THAT THE CIRCULATION IS
SOMEWHAT ELONGATED FROM EAST TO WEST.  STRONGEST CONVECTION IS
OCCURRING JUST TO THE EAST AND NORTHEAST OF THE ESTIMATED CENTER.
INITIAL MOTION IS A HIGHLY UNCERTAIN 305/9.  THE TRACK FORECAST
REASONING IS NOT MUCH DIFFERENT FROM EARLIER TODAY.  FAY IS LIKELY
TO TURN TOWARD THE NORTH ON THE WESTERN PERIPHERY OF A MID-LEVEL
RIDGE.  NOAA G-IV JET DATA SHOW MID-TROPOSPHERIC HEIGHT FALLS OVER
THE SOUTHEASTERN GULF OF MEXICO WHICH ALSO SUPPORTS A TURN TOWARD
THE NORTH.  SOME OF THE TRACK MODELS SUCH AS THE GFDL MODEL HAVE
SHIFTED...ONCE AGAIN...TO THE EAST.  THERE HAVE OBVIOUSLY BEEN SOME
RUN-TO-RUN CONSISTENCY PROBLEMS WITH OUR TRACK GUIDANCE...BUT THIS
IS OFTEN THE CASE FOR WEAK TROPICAL CYCLONES IN THE MODEL INITIAL
CONDITIONS.  I HAVE NOT MADE MUCH OF A CHANGE TO THE OFFICIAL
FORECAST WHICH REMAINS CLOSE TO THE DYNAMICAL MODEL CONSENSUS.

WE HAVE BEEN CARRYING 45 KT FOR THE CURRENT INTENSITY SINCE EARLIER
TODAY ALTHOUGH THERE HAVE BEEN NO RECENTLY OBSERVED FLIGHT-LEVEL
WINDS TO SUPPORT THIS VALUE.  HOWEVER IT IS BELIEVED THAT THESE
WINDS ARE LIKELY OCCURRING IN THE STRONG CONVECTION NORTHEAST OF
THE CENTER WHICH WAS NOT SAMPLED BY THE AIRCRAFT.  AN UPPER-LEVEL
LOW OVER THE EXTREME NORTHWESTERN CARIBBEAN SEA IS IMPEDING THE
OUTFLOW OVER THE WESTERN PORTION OF THE TROPICAL CYCLONE AND MAY
EVEN BE CAUSING SOME UPPER-LEVEL CONVERGENCE OVER THE STORM.  ON
THE OTHER HAND...THE SHIPS GUIDANCE INDICATES THAT VERTICAL SHEAR
WILL DECREASE DURING THE NEXT DAY OR SO.  THEREFORE SOME
STRENGTHENING IS FORECAST WHILE FAY IS OVER WATER DURING THE
EARLIER PART OF THE FORECAST PERIOD.  BY 48 HOURS OR SO...SHEAR
ASSOCIATED WITH AN UPPER-LEVEL TROUGH OVER THE EXTREME EASTERN GULF
OF MEXICO IS FORECAST TO INCREASE...AND THIS SHOULD LIMIT
INTENSIFICATION.  THE OFFICIAL INTENSITY FORECAST IS A BLEND OF THE
LATEST GFDL AND HWRF MODEL PREDICTIONS.  IT SHOULD BE ADDED THAT
THERE IS LOW CONFIDENCE IN THIS FORECAST HOWEVER.

IT IS IMPORTANT NOT TO FOCUS ON THE EXACT FORECAST TRACK.  A BETTER
WAY OF ASSESSING YOUR RISK IS TO MAKE USE OF THE WIND SPEED
PROBABILITIES.  THESE DO NOT CHANGE SIGNIFICANTLY FOR GIVEN
LOCATIONS WHEN SMALL ADJUSTMENTS ARE MADE TO THE TRACK FORECAST.

FORECAST POSITIONS AND MAX WINDS

INITIAL      18/0300Z 21.4N  80.6W    45 KT
 12HR VT     18/1200Z 22.3N  81.7W    50 KT...INLAND
 24HR VT     19/0000Z 23.8N  82.7W    55 KT
 36HR VT     19/1200Z 25.3N  82.8W    65 KT
 48HR VT     20/0000Z 27.0N  82.8W    70 KT
 72HR VT     21/0000Z 30.5N  82.5W    50 KT...INLAND
 96HR VT     22/0000Z 34.0N  82.5W    25 KT...INLAND
120HR VT     23/0000Z 37.5N  82.5W    20 KT...REMNANT LOW

$$
FORECASTER PASCH/ROBERTS



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