000
WTNT42 KNHC 012031
TCDAT2
 
TROPICAL STORM KATIA DISCUSSION NUMBER  15
NWS NATIONAL HURRICANE CENTER MIAMI FL       AL122011
500 PM AST THU SEP 01 2011

KATIA HAS TAKEN THE APPEARANCE OF A SHEARED TROPICAL CYCLONE.
VISIBLE AND MICROWAVE SATELLITE IMAGERY CONTINUE TO INDICATE THAT
THE LOW-LEVEL CENTER IS DISPLACED TO THE WEST OF THE CONVECTION.
THE CURVED BAND THAT WAS LOCATED SOUTH OF THE CENTER HAS
DISSIPATED...AND CONVECTION IS NOW LIMITED TO THE NORTHEAST
QUADRANT OF THE SYSTEM. BASED ON A BLEND OF DVORAK CI AND T NUMBERS
FROM SAB AND TAFB...THE INTENSITY HAS BEEN LOWERED TO 60 KT FOR
THIS ADVISORY.

UW-CIMMS SHEAR ANALYSIS CONTINUES TO INDICATE THAT SOUTHWESTERLY
SHEAR OF ABOUT 15 KT IS CURRENTLY IMPACTING KATIA. AN UPPER-LEVEL
LOW LOCATED TO THE NORTHWEST OF THE CYCLONE APPEARS TO BE THE
PRIMARY SOURCE OF THIS SHEAR. KATIA IS EXPECTED TO CONTINUE TO
INTERACT WITH THIS LOW FOR THE NEXT 24 TO 36 HOURS. AFTER
THAT...THE UPPER-LEVEL LOW IS EXPECTED TO LIFT TO THE
NORTH...RESULTING IN A MORE CONDUCIVE ENVIRONMENT FOR
INTENSIFICATION. THE OFFICIAL FORECAST HAS BEEN LOWERED SLIGHTLY
DUE TO THE MARGINAL ENVIRONMENTAL CONDITIONS IN THE SHORT
TERM...HOWEVER IT STILL BRINGS KATIA TO A MAJOR HURRICANE IN A FEW
DAYS.

KATIA CONTINUES TO MOVE TO THE WEST AT 16 KT. IT IS EXPECTED TO SLOW
DOWN AND BEGIN A GRADUAL TURN TO THE NORTHWEST AS IT APPROACHES A
WEAKNESS IN THE SUBTROPICAL RIDGE. THE GFS...ECMWF...AND HFIP
CONSENSUS MODELS ARE IN GOOD AGREEMENT FOR THE FIRST 3 DAYS. AFTER
THAT THERE IS MORE UNCERTAINTY IN THE FORECAST AS THE MODEL SPREAD
INCREASES. SOME MODELS SUGGEST A TURN TOWARD THE WEST AS THE
SUBTROPICAL RIDGE REBUILDS TO THE NORTH OF KATIA...WHILE OTHERS
SUGGEST THAT THE WEAKNESS WILL PERSIST...BRINGING THE CYCLONE
FARTHER NORTH. THE OFFICIAL FORECAST LIES BETWEEN THESE SCENARIOS
AND IS VERY CLOSE TO THE HFIP CONSENSUS. 

FORECAST POSITIONS AND MAX WINDS
 
INIT  01/2100Z 16.1N  49.2W   60 KT  70 MPH
 12H  02/0600Z 16.8N  51.0W   65 KT  75 MPH
 24H  02/1800Z 17.7N  52.9W   70 KT  80 MPH
 36H  03/0600Z 18.7N  54.6W   75 KT  85 MPH
 48H  03/1800Z 19.7N  56.1W   85 KT 100 MPH
 72H  04/1800Z 21.6N  59.0W   95 KT 110 MPH
 96H  05/1800Z 23.5N  62.0W  100 KT 115 MPH
120H  06/1800Z 25.5N  65.0W  105 KT 120 MPH
 
$$
FORECASTER ZELINSKY/CANGIALOSI