[Tropical] Tropical Cyclone Discussion

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WTNT42 KNHC 032052
TCDAT2

TROPICAL STORM KATIA DISCUSSION NUMBER  23
NWS NATIONAL HURRICANE CENTER MIAMI FL       AL122011
500 PM AST SAT SEP 03 2011

DVORAK INTENSITY ESTIMATES HAVE FALLEN THROUGH THE DAY AND ARE NOW
T3.0/4.0 FROM TAFB AND T3.5/3.5 FROM SAB.  BASED ON THE STRUCTURE
NOTED IN EARLIER MICROWAVE DATA...IT APPEARS THAT KATIA HAS
WEAKENED SOME AND AGAIN IS A TROPICAL STORM.  FLUCTUATIONS IN
INTENSITY BY 5 TO 10 KT ARE POSSIBLE OVER THE NEXT DAY OR SO...BUT
THIS FACT WILL ONLY BE MORE APPARENT THAN USUAL SINCE THE INTENSITY
WOULD BE OSCILLATING AROUND THE 65-KT HURRICANE THRESHOLD.

IT CANNOT BE STRESSED ENOUGH THAT THERE IS CONSIDERABLE UNCERTAINTY
IN THE TRACK FORECAST...WHICH IS EXTREMELY SENSITIVE TO THE
EVOLUTION OF TROPICAL STORM LEE AND ITS INTERACTION WITH A MID-
TO UPPER-LEVEL LOW OVER THE EASTERN UNITED STATES.  THE MODEL
GUIDANCE IS IN PRETTY GOOD AGREEMENT DURING THE FIRST 36 HOURS OR
SO...BUT THE DIVERGENCE ONLY GROWS FROM THERE.  COMPARED TO THE
PREVIOUS FORECAST CYCLE...THE UKMET HAS SHIFTED TO THE NORTH AND
THE GFS HAS SLOWED DOWN...WHICH NORMALLY WOULD HAVE INCREASED
CONFIDENCE IN THE FORECAST.  FURTHERMORE...THE ECMWF...WHICH IS
NORMALLY RELIABLE...SWUNG FROM THE NORTH AND EAST SIDE OF THE
GUIDANCE TO THE SOUTH AND WEST SIDE...SHOWING A MORE WESTWARD
MOTION BY DAY 5.  THE OFFICIAL TRACK FORECAST HAS BEEN NUDGED A BIT
TO THE WEST TOWARDS THE VARIOUS CONSENSUS MODELS...BUT WE WOULD
RATHER SEE SOME STABILITY IN THE MODELS BEFORE MAKING A LARGER
SHIFT.

NEEDLESS TO SAY...THE INTENSITY FORECAST IS ALSO COMPLEX.  KATIA HAS
NOT BEEN STRENGTHENING AS ANTICIPATED...AND UPPER-LEVEL WINDS DO
NOT APPEAR AS THOUGH THEY WILL BE CONDUCIVE FOR SIGNIFICANT
INTENSIFICATION FOR THE NEXT 24 TO 48 HOURS.  THE UPPER-LEVEL
ENVIRONMENT AROUND KATIA BECOMES MORE UNCERTAIN AFTER
THAT TIME DEPENDING ON THE POSITIONING OF THE EASTERN U.S.
MID-/UPPER-LEVEL LOW.  THE STATISTICAL SHIPS AND LGEM MODELS DO NOT
STRENGTHEN KATIA BEYOND CATEGORY 1 STATUS WHEREAS THE GFDL AND HWRF
STILL SHOW THE STORM REACHING MAJOR HURRICANE STRENGTH.  THE
OFFICIAL INTENSITY FORECAST IS STILL NEAR OR JUST ABOVE THE
INTENSITY CONSENSUS...ESPECIALLY AT DAYS 4 AND 5.

FORECAST POSITIONS AND MAX WINDS

INIT  03/2100Z 19.9N  56.8W   60 KT  70 MPH
 12H  04/0600Z 20.7N  58.1W   65 KT  75 MPH
 24H  04/1800Z 21.8N  59.8W   65 KT  75 MPH
 36H  05/0600Z 23.1N  61.5W   70 KT  80 MPH
 48H  05/1800Z 24.3N  63.2W   75 KT  85 MPH
 72H  06/1800Z 27.0N  66.0W   85 KT 100 MPH
 96H  07/1800Z 29.5N  69.0W   90 KT 105 MPH
120H  08/1800Z 31.5N  70.5W   85 KT 100 MPH

$$
FORECASTER BERG


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