[Tropical] Tropical Cyclone Discussion

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WTNT42 KNHC 051447
TCDAT2

HURRICANE KATIA DISCUSSION NUMBER  30
NWS NATIONAL HURRICANE CENTER MIAMI FL       AL122011
1100 AM AST MON SEP 05 2011

KATIA APPEARS TO HAVE GONE THROUGH AN EYEWALL REPLACEMENT AND NOW
HAS A 30 N MI WIDE EYE SURROUNDED BY A RELATIVELY NARROW BAND OF
THE COLDEST CLOUD TOPS.  DVORAK INTENSITY ESTIMATES HAVE RISEN TO
T5.0 FROM TAFB AND SAB...AND THE OBJECTIVE NUMBERS ARE AT T5.5.
THE INITIAL INTENSITY IS THEREFORE BEING RAISED TO 95 KT.

THE EYE HAS BEEN WOBBLING A BIT...BUT THE 12-HOUR SMOOTHED MOTION IS
310/11 KT.  KATIA IS MOVING AROUND THE SOUTHWESTERN PERIPHERY OF A
CENTRAL ATLANTIC MID-LEVEL ANTICYCLONE AND TOWARDS DEEP-LAYER
TROUGHING OVER THE EASTERN UNITED STATES AND WESTERN ATLANTIC.  THE
TRACK GUIDANCE IS IN GOOD AGREEMENT IN MAINTAINING A NORTHWESTWARD
HEADING WITH SOME DECREASE IN FORWARD SPEED DURING THE FIRST 48
HOURS.  ALTHOUGH ALL THE GUIDANCE SHOWS SHARP RE-CURVATURE BETWEEN
BERMUDA AND THE U.S. EAST COAST IN ABOUT 3 DAYS...THERE IS STILL A
LARGE DIVERGENCE IN FORWARD SPEED WITH GREATER-THAN-NORMAL SPREAD
AT DAYS 4 AND 5.  FOR THIS CYCLE...THE GUIDANCE IS BOUNDED BY THE
SLOWER-MOVING ECMWF AND UKMET...AND THE FASTER-MOVING GFS. IF
TRENDS FROM THE PAST FEW DAYS CONTINUE TODAY...I WOULD EXPECT
THE 12Z GUIDANCE TO SHOW LESS SPREAD AND FOR NOW WILL MAINTAIN THE
OFFICIAL FORECAST AS BEING SLOWER THAN THE CONSENSUS MODELS.

THE UPPER-LEVEL ENVIRONMENT NEAR KATIA APPEARS CONDUCIVE FOR FURTHER
STRENGTHENING OVER THE NEXT SEVERAL DAYS.  HOWEVER...WITHIN THE NEXT
24 HOURS OR SO...THE HURRICANE WILL BE MOVING OVER OCEAN HEAT
CONTENT VALUES THAT DO NOT NORMALLY SUPPORT SIGNIFICANT
INTENSIFICATION.  THE OFFICIAL FORECAST THEREFORE INDICATES GRADUAL
STRENGTHENING OVER THE NEXT 24 HOURS AND THEN MAINTAINS THE
INTENSITY THROUGH DAYS 2 AND 3.  WEAKENING IS FORECAST ON DAYS 4
AND 5 AS VERTICAL SHEAR INCREASES...AND AS KATIA MOVES OVER EVEN
LESS CONDUCIVE OCEAN WATERS.  THE OFFICIAL INTENSITY FORECAST IS AT
THE UPPER END OF THE GUIDANCE FOR MOST OF THE FORECAST PERIOD.

DUE TO THE EYEWALL REPLACEMENT...IT APPEARS THAT THE WIND FIELD HAS
EXPANDED A BIT...AND THIS IS REFLECTED IN THE ANALYSIS AND FORECAST.

FORECAST POSITIONS AND MAX WINDS

INIT  05/1500Z 24.6N  63.3W   95 KT 110 MPH
 12H  06/0000Z 25.6N  64.2W  100 KT 115 MPH
 24H  06/1200Z 26.9N  65.7W  105 KT 120 MPH
 36H  07/0000Z 28.1N  67.3W  105 KT 120 MPH
 48H  07/1200Z 29.2N  68.7W  100 KT 115 MPH
 72H  08/1200Z 32.5N  70.5W   95 KT 110 MPH
 96H  09/1200Z 37.0N  67.5W   80 KT  90 MPH
120H  10/1200Z 40.0N  60.0W   70 KT  80 MPH

$$
FORECASTER BERG


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