[Tropical] Tropical Cyclone Discussion

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WTNT42 KNHC 040852
TCDAT2

TROPICAL STORM KATIA DISCUSSION NUMBER  25
NWS NATIONAL HURRICANE CENTER MIAMI FL       AL122011
500 AM AST SUN SEP 04 2011

KATIA REMAINS IN A NEARLY STEADY STATE. THE CLOUD PATTERN CONTINUES
TO CONSIST OF A RATHER INDISTINCT CENTRAL DENSE OVERCAST WHICH HAS
BEEN PULSATING SOMEWHAT FREQUENTLY. A COUPLE OF MICROWAVE PASSES
SHOWED THE EXISTENCE OF A MID-LEVEL EYE THAT HAS BEEN LESS DEFINED
IN THE LOW-LEVELS. WITH ESSENTIALLY NO STRUCTURAL CHANGES TO REPORT
AND DVORAK T-NUMBERS THE SAME AS AT 0000 UTC...THE INITIAL
INTENSITY IS HELD AT 60 KT. CIRRUS CLOUD MOTIONS AND UW-CIMSS
ANALYSES SUGGEST A SOUTHWESTERLY FLOW UNDERCUTTING THE OUTFLOW
LAYER...WHICH MAY HAVE BEEN STALLING THE INTENSIFICATION PROCESS.
GLOBAL MODELS CONTINUE TO INSIST ON A MORE CONDUCIVE UPPER AIR
FORECAST AHEAD OF KATIA THAT WOULD FAVOR INTENSIFICATION BEGINNING
IN A COUPLE OF DAYS. THEN AGAIN...THE FORECAST REDUCTION IN SHEAR
BY THIS TIME HAS NOT MATERIALIZED AND IT WOULD SEEM THAT THE MODELS
HAVE CONTINUALLY UNDERFORECAST THE AMOUNT OF SHEAR. THE OFFICIAL
FORECAST WILL KEEP THIS IN MIND AND REPRESENT A MEASURED
APPROACH...BLENDING THE MORE RELIABLE STATISTICAL MODELS INDICATING
MODEST STRENGTHENING AND DYNAMICAL GUIDANCE WHICH STILL FORECASTS
KATIA TO BECOME A MAJOR HURRICANE.

LOCATING THE CENTER HAS BEEN DIFFICULT IN CONVENTIONAL SATELLITE
IMAGERY...BUT A TIMELY AMSR-E PASS HELPED TO ESTABLISH THE INITIAL
MOTION ESTIMATE OF 305/10.  WATER VAPOR IMAGERY SHOWS KATIA HEADING
NORTHWESTWARD TOWARD A MID- TO UPPER-LEVEL IMPULSE LOCATED OVER THE
WESTERN ATLANTIC.  ALTHOUGH THE LARGE-SCALE MODELS FORECAST THIS
FEATURE TO LIFT OUT DURING THE NEXT DAY OR TWO...THEY ALSO FORECAST
A WEAKNESS OVER THIS REGION TO REMAIN IN PLACE WHICH SHOULD CAUSE
KATIA TO CONTINUE ON A NORTHWESTWARD COURSE AND SLOW DURING THE
NEXT SEVERAL DAYS.  THE LONGER-TERM TRACK OF KATIA SEEMS DEPENDENT
ON THE TROUGH ASSOCIATED WITH THE REMNANTS OF LEE AND A PROCESSION
OF SHORTWAVE TROUGHS MOVING THROUGH THE NORTHEASTERN UNITED
STATES...BOTH OF WHICH THE MODELS ARE HANDLING DIFFERENTLY TO
VARYING DEGREES.  THERE HAS BEEN A SIGNIFICANT WESTWARD SHIFT IN
THE GUIDANCE THIS CYCLE...ALONG WITH A NOTABLE INCREASE IN THE
SPREAD.  THE OFFICIAL TRACK AT THIS LONGER RANGE IS OF SOMEWHAT
LOWER CONFIDENCE...GIVEN THE SPREAD...AND IS ADJUSTED TO THE
LEFT...BUT NOT AS FAR LEFT AS THE LATEST MULTI-MODEL CONSENSUS.



FORECAST POSITIONS AND MAX WINDS

INIT  04/0900Z 21.4N  58.5W   60 KT  70 MPH
 12H  04/1800Z 22.3N  59.8W   65 KT  75 MPH
 24H  05/0600Z 23.5N  61.6W   70 KT  80 MPH
 36H  05/1800Z 24.7N  63.5W   75 KT  85 MPH
 48H  06/0600Z 25.8N  65.0W   80 KT  90 MPH
 72H  07/0600Z 27.7N  68.0W   85 KT 100 MPH
 96H  08/0600Z 30.0N  71.0W   90 KT 105 MPH
120H  09/0600Z 32.5N  72.0W   85 KT 100 MPH

$$
FORECASTER KIMBERLAIN


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