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Hurricane KATIA (Text)

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HURRICANE KATIA DISCUSSION NUMBER  20
NWS NATIONAL HURRICANE CENTER MIAMI FL       AL122011
1100 PM AST FRI SEP 02 2011
 
A SERIES OF MICROWAVE IMAGES DURING THE LATE AFTERNOON CLEARLY
SHOWED THE MID-LEVEL CENTER DISPLACED TO THE NORTH OF THE LOW-LEVEL
ONE. THIS MEANS THAT KATIA CONTINUES SUFFERING FROM SOUTHERLY SHEAR
AND HAS NOT INTENSIFIED. THE CLOUD PATTERN IS NOT VERY IMPRESSIVE
FOR A HURRICANE...BUT THE INITIAL INTENSITY IS CONSERVATIVELY KEPT
AT 65 KNOTS BASED ON T-NUMBERS FROM TAFB AND SAB. THERE IS A
SIGNIFICANT EXPANSION OF THE OUTFLOW IN THE WESTERN SEMICIRCLE
GIVING THE FALSE IMPRESSION THAT THE SHEAR IS WEAKENING. THIS IS
EXPECTED TO BE TRANSIENT SINCE WATER VAPOR IMAGES STILL SHOW THAT
THE UPPER-LEVEL TROUGH CAUSING THE SHEAR IS STILL THERE...AND
GLOBAL MODELS BASICALLY KEEP POSTPONING ITS WEAKENING.  ACTUALLY...
THE SHIPS MODEL INDICATE THAT UPPER-LEVEL WIND ENVIRONMENT WILL
REMAIN HOSTILE FOR 24 TO 36 HOURS...WHILE THE ECMWF KEEPS IT
HOSTILE EVEN LONGER. ON THIS BASIS...THE OFFICIAL FORECAST CALLS
FOR NO CHANGE IN INTENSITY FOR ABOUT TWO DAYS AND FOR STRENGTHENING
THEREAFTER.

KATIA IS MOVING TOWARD THE NORTHWEST OR 305 DEGREES AT 10 KNOTS.
GLOBAL MODELS UNANIMOUSLY BUILD THE SUBTROPICAL RIDGE WESTWARD AND
WEAKEN THE TROUGH OVER THE WESTERN ATLANTIC. THIS FORECAST PATTERN
CALLS FOR A GENERAL NORTHWEST TO WEST-NORTHWEST TRACK WITH NO
SIGNIFICANT CHANGE IN SPEED THROUGH FIVE DAYS AS INDICATED IN THE
NHC FORECAST. WITH THE EXCEPTION OF THE UK MODEL WHICH BUILDS A
STRONGER SUBTROPICAL RIDGE THAN THE OTHER MODELS AND KEEPS KATIA ON
A MORE WESTWARD TRACK...THE REST OF THE TRACK MODELS ARE IN GOOD
AGREEMENT. THE OFFICIAL FORECAST IS IN THE MIDDLE OF THE GUIDANCE
ENVELOPE AND IS VERY CLOSE TO THE ECMWF AND THE GFS GLOBAL MODELS.
 
  
FORECAST POSITIONS AND MAX WINDS
 
INIT  03/0300Z 18.5N  54.3W   65 KT  75 MPH
 12H  03/1200Z 19.5N  55.4W   65 KT  75 MPH
 24H  04/0000Z 20.5N  57.0W   65 KT  75 MPH
 36H  04/1200Z 21.5N  59.0W   65 KT  75 MPH
 48H  05/0000Z 22.5N  60.5W   75 KT  85 MPH
 72H  06/0000Z 24.5N  63.5W   85 KT 100 MPH
 96H  07/0000Z 26.5N  66.5W   95 KT 110 MPH
120H  08/0000Z 28.0N  69.5W   95 KT 110 MPH
 
$$
FORECASTER AVILA
 
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