[Tropical] Tropical Cyclone Discussion

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WTNT42 KNHC 312039
TCDAT2

TROPICAL STORM KATIA DISCUSSION NUMBER  11
NWS NATIONAL HURRICANE CENTER MIAMI FL       AL122011
500 PM AST WED AUG 31 2011

KATIA IS NEAR THE THRESHOLD OF HURRICANE STATUS.  THE SYSTEM
CONTINUES TO EXHIBIT PROMINENT CURVED CONVECTIVE BANDS AND DEEP
CONVECTION IS BECOMING STRONGER OVER THE CENTER.  THE STORM ALSO
HAS A FAIRLY SYMMETRIC AND WELL-ESTABLISHED UPPER-LEVEL OUTFLOW
PATTERN.  DVORAK INTENSITY ESTIMATES FROM BOTH AGENCIES REMAIN AT
55 KT...BUT AMSU INTENSITY ESTIMATES FROM THE UNIVERSITY OF
WISCONSIN CIMSS ARE A LITTLE HIGHER.  THE INTENSITY IS SET AT 60 KT
FOR THIS ADVISORY.  WEAK VERTICAL SHEAR AND MODESTLY WARM WATERS
ARE LIKELY TO PREVAIL OVER THE NEXT FEW DAYS...SO CONTINUED
INTENSIFICATION IS FORECAST.  A LARGE UPPER-LEVEL LOW TO THE
NORTHWEST OF KATIA COULD CAUSE AN INCREASE IN SHEAR...AND INHIBIT
INTENSIFICATION...LATE IN THE FORECAST PERIOD.  HOWEVER SOME OF THE
GLOBAL MODELS...SUCH AS THE GFS...SUGGEST THAT THE OUTFLOW
ANTICYCLONE OF KATIA WILL DOMINATE THE UPPER-LEVEL WIND PATTERN AND
DISPLACE THE SHEARING FLOW ASSOCIATED WITH THE LOW.  IF THAT
OCCURS...KATIA WOULD LIKELY BECOME A MAJOR HURRICANE BY DAY 4 OR 5.
THE OFFICIAL INTENSITY FORECAST IS SIMILAR TO THE PREVIOUS ONE AND
SLIGHTLY HIGHER THAN THE STATISTICAL-DYNAMICAL GUIDANCE.

THE STORM CONTINUES TO MOVE WEST-NORTHWESTWARD ON THE SOUTH SIDE OF
A SUBTROPICAL ANTICYCLONE.  THE TRACK FORECAST AND REASONING ARE
ESSENTIALLY UNCHANGED.  AS KATIA NEARS THE SOUTHWEST SIDE OF THE
ANTICYCLONE...A GRADUAL TURN TOWARD THE NORTHWEST WITH DECREASING
FORWARD SPEED IS LIKELY.  THE CURRENT OFFICIAL TRACK FORECAST IS AN
UPDATE OF THE PREVIOUS ONE AND ABOUT IN THE MIDDLE OF THE GUIDANCE
ENVELOPE.  IT IS ALSO A LITTLE TO THE WEST OF THE GFS AND ECMWF
SOLUTIONS.

FORECAST POSITIONS AND MAX WINDS

INIT  31/2100Z 14.6N  42.6W   60 KT  70 MPH
 12H  01/0600Z 15.1N  44.9W   65 KT  75 MPH
 24H  01/1800Z 15.8N  47.7W   75 KT  85 MPH
 36H  02/0600Z 16.6N  50.0W   85 KT 100 MPH
 48H  02/1800Z 17.7N  52.0W   90 KT 105 MPH
 72H  03/1800Z 20.0N  55.5W   95 KT 110 MPH
 96H  04/1800Z 22.0N  58.5W  100 KT 115 MPH
120H  05/1800Z 23.5N  61.0W  105 KT 120 MPH

$$
FORECASTER PASCH


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