[Tropical] Tropical Cyclone Discussion

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WTNT42 KNHC 060337
TCDAT2

HURRICANE KATIA DISCUSSION NUMBER  32...CORRECTED
NWS NATIONAL HURRICANE CENTER MIAMI FL       AL122011
1100 PM AST MON SEP 05 2011

CORRECTED FOR STATUS AT 120 HOUR FORECAST IN TABLE

SATELLITE IMAGES INDICATE THAT KATIA HAS STRENGTHENED CONSIDERABLY
DURING THE PAST SEVERAL HOURS. AS THE ASSOCIATED DEEP CONVECTION
BECAME MUCH MORE SYMMETRIC AND THE EYE WARMED DURING THE EVENING
HOURS...DVORAK CLASSIFICATIONS FROM TAFB AND SAB INCREASED TO
6.0/115 KT AT 0000 UTC. DESPITE SOME FLUCTUATIONS IN THE APPEARANCE
OF THE EYE OVER THE LAST HOUR OR TWO...ADT ESTIMATES FROM UW-CIMSS
ARE STILL 6.2/122 KT...SO THE INITIAL INTENSITY IS INCREASED TO 115
KT...MAKING KATIA A CATEGORY FOUR HURRICANE.

THE LATEST 12-HOUR INITIAL MOTION ESTIMATE IS 315/9...A TOUCH SLOWER
THAN NOTED IN THE PREVIOUS PACKAGE. THE TRACK FORECAST REASONING IS
UNCHANGED. KATIA IS EXPECTED TO CONTINUE MOVING NORTHWESTWARD FOR
THE NEXT 36 HOURS AS IT REMAINS ON THE SOUTHWESTERN PERIPHERY OF
THE SUBTROPICAL RIDGE. A TURN TOWARD THE NORTH IS FORECAST IN 48 TO
72 HOURS AS THE HURRICANE BECOMES EMBEDDED IN SOUTHERLY FLOW
BETWEEN THE RIDGE AND A LARGE CUTOFF LOW OVER THE EASTERN UNITED
STATES. THIS STEERING PATTERN WILL ALLOW KATIA TO MOVE BETWEEN
BERMUDA AND THE UNITED STATES EAST COAST DURING THAT TIME PERIOD.
AFTER THAT...A SHARP NORTHEASTWARD AND EAST-NORTHEASTWARD TURN WITH
AN INCREASE IN FORWARD SPEED IS FORECAST AS KATIA GETS CAUGHT IN
THE MID-LATITUDE WESTERLIES. THE MODEL SOLUTIONS HAVE BEEN
CONVERGING DURING THE PAST FEW CYCLES AND ARE NOW IN RELATIVELY
GOOD AGREEMENT...INCREASING CONFIDENCE IN THE TRACK FORECAST. THE
OFFICIAL FORECAST IS SIMILAR TO THE PREVIOUS ONE AND NEAR THE
MIDDLE OF THE GUIDANCE ENVELOPE.

FLUCTUATIONS IN THE INTENSITY OF KATIA ARE LIKELY DURING THE NEXT 12
TO 24 HOURS...PERHAPS DUE TO EYEWALL REPLACEMENT CYCLES...AS THE
MAJOR HURRICANE REMAINS IN A FAVORABLE ENVIRONMENT. SLOW WEAKENING
IS EXPECTED BEYOND THAT TIME AS KATIA MOVES INTO AN ENVIRONMENT OF
MODERATE SHEAR AND SLIGHTLY COOLER WATERS. THE NEW NHC INTENSITY
FORECAST HAS BEEN ADJUSTED UPWARD THROUGH 36 HOURS BASED ON THE
OBSERVED STRENGTHENING AND IS NEAR THE MODEL CONSENSUS. KATIA IS
NOW FORECAST TO BE A POST-TROPICAL CYCLONE BY DAY 5...AS IT IS
EXPECTED TO BE WELL-EMBEDDED IN THE WESTERLIES AND OVER 20-21C
WATERS BY THAT TIME.

DRIFTING BUOY 41855...WHICH WAS LOCATED ABOUT 20 N MI NORTHEAST OF
THE EYE OF KATIA AT 0000 UTC...REPORTED A MINIMUM PRESSURE OF 952
MB.

FORECAST POSITIONS AND MAX WINDS

INIT  06/0300Z 25.8N  64.4W  115 KT 135 MPH
 12H  06/1200Z 26.9N  65.5W  115 KT 135 MPH
 24H  07/0000Z 28.1N  66.9W  115 KT 135 MPH
 36H  07/1200Z 29.4N  68.3W  110 KT 125 MPH
 48H  08/0000Z 30.9N  69.5W  100 KT 115 MPH
 72H  09/0000Z 35.4N  69.7W   90 KT 105 MPH
 96H  10/0000Z 39.5N  63.5W   75 KT  85 MPH
120H  11/0000Z 42.5N  48.0W   65 KT  75 MPH...POST-TROP/EXTRATROP

$$
FORECASTER CANGIALOSI



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