[Tropical] Tropical Cyclone Discussion

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WTNT42 KNHC 280250
TCDAT2
TROPICAL STORM GUSTAV DISCUSSION NUMBER  12
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL   AL072008
1100 PM EDT WED AUG 27 2008

THE LAST RECONNAISSANCE FIX WAS AT 23Z.  DATA FROM THE AIRCRAFT
INDICATED THAT THE CENTER OF GUSTAV BEGAN TO MOVE WEST-
SOUTHWESTWARD AND AWAY FROM THE DEEP CONVECTION.  PEAK FLIGHT-LEVEL
WINDS WERE 39 KT AND THE HIGHEST RECENT BELIEVABLE SFMR WINDS WERE
41 KT.  THE ADVISORY INTENSITY IS LOWERED TO 40 KT BASED ON THESE
OBSERVATIONS.

THE INITIAL MOTION IS NOW ESTIMATED TO BE 250/7...ALTHOUGH THE
CENTER HAS BEEN VERY HARD TO TRACK SINCE THE TIME OF THE LAST FIX
AND MIGHT BE A LITTLE SOUTH OF MY ADVISORY POSITION.  A DEEP-LAYER
RIDGE...ORIENTED NORTHEAST-SOUTHWEST...IS CENTERED OVER THE FLORIDA
PENINSULA. THIS RIDGE HAS IMPARTED A BIT OF A SOUTHERLY COMPONENT
OF MOTION THAT SOME MODELS SHOW PERSISTING FOR ANOTHER 24 HOURS OR
SO. AFTER THAT...GUSTAV IS EXPECTED TO ROUND THE PERIPHERY OF THE
RIDGE AND TURN TO THE NORTHWEST IN THE EASTERN GULF OF MEXICO.
COMPLICATING THE FORECAST IN THE LATTER PART OF THE PERIOD IS THE
EVOLUTION AND IMPACT OF AN UPPER-LEVEL TROUGH EXPECTED TO BE IN THE
CENTRAL OR WESTERN GULF OF MEXICO...AS WELL AS THE DEVELOPMENT OF A
BLOCKING HIGH AT THE END OF THE PERIOD REMINISCENT OF WHAT HAPPENED
WITH FAY A WEEK OR SO AGO. GIVEN THESE FACTORS...THE MODEL GUIDANCE
IS IN SURPRISINGLY GOOD AGREEMENT. THE OFFICIAL FORECAST RELIES
MOST STRONGLY ON A BLEND OF THE ECMWF...UKMET...GFDL...AND
GFS...WHICH IS NOW FOLLOWING THE VORTEX FAIRLY WELL...AND IS JUST
TO THE LEFT OF THE PREVIOUS ADVISORY TRACK. THE DYNAMICAL MODEL
CONSENSUS IS A LITTLE FARTHER TO THE LEFT.

GUSTAV HAS BEEN SIGNIFICANTLY DISPRUPTED BY ITS ENCOUNTER WITH THE
TERRAIN OF HAITI.  IN ADDITION...MID-LEVEL DRY AIR APPEARS TO BE
OVERTAKING THE CYCLONE FROM THE NORTHEAST.   IN ANOTHER 24-36
HOURS...HOWEVER...GUSTAV SHOULD FIND ITSELF UNDER AN UPPER
ANTICYCLONE AND OVER THE VERY DEEP WARM WATERS OF THE NORTHWESTERN
CARIBBEAN...AND SO THE CYCLONE SHOULD HAVE AN OPPORTUNITY TO
RESTRENGTHEN.  IN ADDITION...THE FORECAST TRACK TAKES GUSTAV OVER
THE LOOP CURRENT IN THE SOUTHEASTERN GULF.  AFTER THAT...GLOBAL
MODELS SUGGEST THE POSSIBILITY OF SOUTHWESTERLY SHEAR IN THE GULF
ASSOCIATED WITH THE UPPER TROUGH THAT COULD SLOW THE
INTENSIFICATION RATE.  THE OFFICIAL FORECAST SHOWS A SLOWER
RESTRENGTHENING THAN THE PREVIOUS ADVISORY INITIALLY...BUT IS
OTHERWISE SIMILAR...AND ROUGHLY SPLITS THE DIFFERENCE BETWEEN THE
SHIPS AND GFDL GUIDANCE.

IT PROBABLY WOULDN'T HURT TO REMIND EVERYONE THAT THE AVERAGE 5-DAY
OFFICIAL TRACK ERROR IS ABOUT 300 MILES...AND THE AVERAGE 5-DAY
INTENSITY ERROR IS ABOUT 25 MPH.


FORECAST POSITIONS AND MAX WINDS

INITIAL      28/0300Z 18.8N  75.4W    40 KT
 12HR VT     28/1200Z 18.8N  76.5W    45 KT
 24HR VT     29/0000Z 18.9N  78.0W    50 KT
 36HR VT     29/1200Z 19.4N  79.5W    60 KT
 48HR VT     30/0000Z 20.1N  81.0W    70 KT
 72HR VT     31/0000Z 22.5N  84.5W    85 KT
 96HR VT     01/0000Z 26.0N  87.5W    95 KT
120HR VT     02/0000Z 29.0N  89.5W    95 KT

$$
FORECASTER FRANKLIN

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