Hurricane KATIA

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HURRICANE KATIA DISCUSSION NUMBER  21
NWS NATIONAL HURRICANE CENTER MIAMI FL       AL122011
500 AM AST SAT SEP 03 2011
 
KATIA CONTINUES TO STRUGGLE THIS MORNING WITH BURSTS OF CONVECTION
FORMING AN UNSHAPELY CENTRAL DENSE OVERCAST.  THE OVERALL PATTERN
IS NOT WELL ORGANIZED EITHER WITH THE HURRICANE HAVING TROUBLE
MAINTAINING BANDING FEATURES.  SATELLITE CLASSIFICATIONS ARE A
LITTLE LOWER THAN EARLIER...BUT STILL SUPPORT 65 KT ON THIS
ADVISORY. IT WOULD NOT BE SURPRISING IF IT WERE A LITTLE WEAKER
GIVEN THE RAGGED SATELLITE APPEARANCE.
 
SOUTHWESTERLY SHEAR AND SOME DRY AIR CONTINUE TO PREVENT SIGNIFICANT
STRENGTHENING OF THE TROPICAL CYCLONE.  THE UPPER-LEVEL TROUGH TO
THE NORTHWEST OF KATIA...HOWEVER...HAS BEEN WEAKENING...AND MOST OF
THE GLOBAL MODELS SUGGEST THE SHEAR WILL DECREASE STARTING ON
SUNDAY.  THUS SLOW INTENSIFICATION IS INDICATED AT THAT TIME IN THE
NHC FORECAST.  AFTERWARD...VERTICAL WIND SHEAR COULD BECOME RATHER
LOW BY DAY 4 AS AN UPPER-HIGH BUILDS CLOSER TO THE TROPICAL CYCLONE
WHILE KATIA MOVES OVER 29C WATER TEMPERATURES.  THE NHC FORECAST IS
SIMILAR TO THE PREVIOUS ONE EARLY ON...NEAREST THE LGEM/SHIPS
MODELS...BUT THEN IS BLENDED A LITTLE HIGHER AT THE END OF THE
FORECAST PERIOD WITH THE DYNAMICAL MODEL CONSENSUS.   BOTH THE HWRF
AND GFDL ARE SIGNIFICANTLY STRONGER THAN THE NHC FORECAST...BUT
THEY ARE PROBABLY NOT HANDLING THE MODERATE TO STRONG VERTICAL
SHEAR ENVIRONMENT CORRECTLY.
 
KATIA CONTINUES MOVING TOWARD THE NORTHWEST AT ABOUT 9 KT.  ALMOST
ALL OF THE GUIDANCE KEEP THIS GENERAL TRACK GOING FOR THE NEXT
SEVERAL DAYS AS THE CYCLONE APPROACHES THE WESTERN PERIPHERY OF THE
SUBTROPICAL RIDGE.  THE UKMET MODEL HAS BEEN STUBBORNLY FORECASTING
A MUCH STRONGER RIDGE...WHICH FORCES THE CYCLONE ON A WESTWARD
COURSE CLOSER TO THE BAHAMAS.  THIS WESTWARD TRACK SEEMS HIGHLY
UNLIKELY DUE TO A PRONOUNCED TROUGH OVER THE WESTERN ATLANTIC OCEAN
AND THE UKMET SOLUTION IS DISREGARDED FOR THIS FORECAST.  
OTHERWISE...THE MOST RELIABLE GUIDANCE HAS SHIFTED NORTHWARD
TONIGHT...PROBABLY DUE TO THE AFOREMENTIONED TROUGH OVER THE
WESTERN ATLANTIC BEING A BIT STRONGER THAN EARLIER ANTICIPATED. 
THE NHC FORECAST IS NEAR THE PREVIOUS ONE FOR THE FIRST COUPLE OF
DAYS...THEN IS SHIFTED TO THE NORTH...BUT NOT NEARLY AS FAR AS THE
MOST RECENT ECMWF/GFS/GFDL MODEL SOLUTIONS.
 
 
FORECAST POSITIONS AND MAX WINDS
 
INIT  03/0900Z 19.3N  55.1W   65 KT  75 MPH
 12H  03/1800Z 20.1N  56.3W   65 KT  75 MPH
 24H  04/0600Z 21.1N  57.9W   65 KT  75 MPH
 36H  04/1800Z 22.2N  59.7W   70 KT  80 MPH
 48H  05/0600Z 23.4N  61.5W   75 KT  85 MPH
 72H  06/0600Z 26.0N  64.5W   90 KT 105 MPH
 96H  07/0600Z 28.5N  67.5W  100 KT 115 MPH
120H  08/0600Z 31.0N  70.0W   95 KT 110 MPH
 
$$
FORECASTER BLAKE
 
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