000
WTNT42 KNHC 071448
TCDAT2
 
HURRICANE KATIA DISCUSSION NUMBER  38
NWS NATIONAL HURRICANE CENTER MIAMI FL       AL122011
1100 AM AST WED SEP 07 2011
 
THE CLOUD PATTERN OF KATIA HAS CHANGED LITTLE SINCE EARLY
THIS MORNING. RECENT MICROWAVE IMAGES SHOW THE REMAINING
FRAGMENTS OF AN INNER EYE WALL WITH A COUPLE OF CONVECTIVE BANDS
OVER THE NORTHEASTERN SEMICIRCLE.  IT APPEARS THAT DRY AIR HAS
WRAPPED AROUND THE SOUTHWESTERN SIDE OF THE CIRCULATION WITH DEEP
CONVECTION NON EXISTENT OVER THAT PORTION OF THE CYCLONE.  THE
DVORAK T- AND CI-NUMBERS FROM TAFB HAVE DECREASED AND CI-NUMBERS
FROM BOTH AGENCIES ARE NOW T4.5.  THIS SUPPORTS LOWERING THE
INITIAL INTENSITY TO 75 KT.  GIVEN THE MODERATE WESTERLY SHEAR AND
THE LACK OF A TIGHT-INNER CORE...SOME SLIGHT WEAKENING IS
ANTICIPATED DURING THE NEXT 24 HOURS.  AS KATIA BEGINS MOVING
NORTH-NORTHEASTWARD IN A DAY OR SO...THE SHIPS GUIDANCE SHOWS THAT
THE SHEAR WILL DECREASE...HOWEVER THE HURRICANE WILL BE MOVING OVER
COOLER SSTS...WHICH SHOULD NEGATE THE SLIGHTLY MORE FAVORABLE
ATMOSPHERIC ENVIRONMENT.  THE OFFICIAL FORECAST CALLS FOR VERY
LITTLE CHANGE IN INTENSITY UNTIL THE SYSTEM BECOMES AN
EXTRATROPICAL CYCLONE IN 3-4 DAYS.
 
THE INITIAL MOTION ESTIMATE IS 315/9.  THE MODELS ARE IN EXCELLENT
AGREEMENT SHOWING A TURN TOWARD THE NORTH DURING THE NEXT 24
HOURS...FOLLOWED BY A TURN TOWARD THE NORTHEAST IN A COUPLE OF
DAYS.  AFTER THAT TIME...THE CYCLONE IS EXPECTED TO ACCELERATE
INTO THE WESTERLIES AHEAD OF A TROUGH THAT MOVES OVER THE CANADIAN
MARITIMES IN 3-4 DAYS.  THE GFS AND ECMWF ARE IN VERY GOOD
AGREEMENT EVEN DURING THE EXTRATROPICAL PORTION OF THE TRACK.  THE
NEW NHC FORECAST IS CLOSE TO THESE RELIABLE MODELS AND ONLY SLIGHT
ADJUSTMENTS WERE MADE TO THE PREVIOUS FORECAST.
 
THE WIND RADII OVER THE NORTHWEST QUADRANT OF THE HURRICANE WERE
EXPANDED OUTWARD BASED ON DATA FROM NOAA BUOY 41048.  THE CENTER OF
KATIA IS FORECAST TO PASS VERY NEAR THAT BUOY TONIGHT.
 
 
FORECAST POSITIONS AND MAX WINDS
 
INIT  07/1500Z 29.2N  68.8W   75 KT  85 MPH
 12H  08/0000Z 30.6N  69.6W   70 KT  80 MPH
 24H  08/1200Z 32.8N  69.8W   70 KT  80 MPH
 36H  09/0000Z 35.4N  69.0W   70 KT  80 MPH
 48H  09/1200Z 38.1N  66.6W   70 KT  80 MPH
 72H  10/1200Z 42.5N  52.5W   65 KT  75 MPH
 96H  11/1200Z 51.0N  29.0W   65 KT  75 MPH...POST-TROP/EXTRATROP
120H  12/1200Z 60.0N   8.0W   65 KT  75 MPH...POST-TROP/EXTRATROP
 
$$
FORECASTER BROWN