[Tropical] Tropical Cyclone Discussion

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WTNT42 KNHC 042048
TCDAT2

HURRICANE KATIA DISCUSSION NUMBER  27
NWS NATIONAL HURRICANE CENTER MIAMI FL       AL122011
500 PM AST SUN SEP 04 2011

WHILE KATIA HAS HAD A FAIRLY WELL-DEFINED EYE IN VISIBLE SATELLITE
IMAGERY...THE INFRARED REPRESENTATION OF THE EYE HAS COME AND GONE
OVER THE PAST FEW HOURS.  DVORAK INTENSITY ESTIMATES AT 1800 UTC
WERE A UNANIMOUS T5.0 FROM TAFB...SAB...AND THE UW-CIMSS ADT...SO
THE INITIAL INTENSITY IS RAISED TO 90 KT FOR THIS ADVISORY.

KATIA HAS TURNED JUST A BIT TO THE RIGHT WITH AN INITIAL MOTION OF
310/10 KT.  COMPARED TO THE PREVIOUS FEW FORECAST CYCLES...THERE IS
CONSIDERABLY MORE AGREEMENT IN THE TRACK MODEL GUIDANCE FOR THIS
PACKAGE.  FOR THE FIRST 48 HOURS...THE GUIDANCE IS TIGHTLY CLUSTERED
AND AGREES ON MAINTAINING KATIA ON A HEADING OF 310 DEGREES WITH
SOME DECELERATION.  THEREAFTER...THERE IS SOME DIVERGENCE BUT NOT
AS MUCH AS THERE WAS EARLIER.  ACTUALLY...THE GFS...ECWMF...AND
UKMET MODELS ARE ALL SHOWING A MID- TO UPPER-LEVEL CLOSED LOW
DEVELOPING OVER THE EASTERN UNITED STATES AND HAVE THE POSITION OF
THE LOW WITHIN 200 N MI OF EACH OTHER BY DAY 5.  THIS CONFIGURATION
SHOULD CAUSE KATIA TO MAKE A TURN TOWARD THE NORTH BY THE END OF
THE FORECAST PERIOD.  THE USUALLY RELIABLE ECMWF HAS SHIFTED A BIT
TO THE EAST AND IS NOW VERY CLOSE TO THE PREVIOUS OFFICIAL
FORECAST.  THEREFORE...LITTLE CHANGE WAS MADE TO THE TRACK FORECAST
FOR THIS CYCLE.

THE PERIOD OF RAPID INTENSIFICATION MAY HAVE LEVELED OFF A BIT...BUT
ENVIRONMENTAL CONDITIONS STILL APPEAR FAVORABLE FOR ADDITIONAL
STRENGTHENING.  THE ONLY APPARENT NEGATIVE FACTORS FOR THIS ARE
RELATIVELY WARM UPPER-TROPOSPHERIC TEMPERATURES AND LOWER OCEANIC
HEAT CONTENT VALUES ALONG THE FORECAST PATH...ESPECIALLY FROM DAYS
3 THROUGH 5.  THE OFFICIAL FORECAST IS STILL AT THE UPPER END OF
THE RANGE OF GUIDANCE VALUES...CLOSE TO THE DYNAMICAL HURRICANE
MODELS...AND INDICATES GRADUAL STRENGTHENING OVER THE NEXT 48
HOURS...FOLLOWED BY GRADUAL WEAKENING ON DAYS 4 AND 5.

LONG-PERIOD SWELLS ASSOCIATED WITH KATIA ARE ALREADY APPROACHING
PARTS OF THE EAST COAST OF THE UNITED STATES.  EVEN IF KATIA DOES
NOT DIRECTLY IMPACT THE UNITED STATES...THE THREAT FOR HIGH SURF
AND RIP CURRENTS ALONG EAST COAST BEACHES IS EXPECTED TO INCREASE
OVER THE NEXT FEW DAYS.  PLEASE CONSULT PRODUCTS ISSUED BY LOCAL
NATIONAL WEATHER SERVICE OFFICES FOR MORE INFORMATION.

FORECAST POSITIONS AND MAX WINDS

INIT  04/2100Z 22.7N  60.1W   90 KT 105 MPH
 12H  05/0600Z 23.7N  61.5W   95 KT 110 MPH
 24H  05/1800Z 25.0N  63.2W  100 KT 115 MPH
 36H  06/0600Z 26.1N  64.7W  100 KT 115 MPH
 48H  06/1800Z 27.1N  66.1W  105 KT 120 MPH
 72H  07/1800Z 29.0N  69.0W  105 KT 120 MPH
 96H  08/1800Z 31.5N  71.5W  100 KT 115 MPH
120H  09/1800Z 34.5N  71.5W   90 KT 105 MPH

$$
FORECASTER BERG



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