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| #456226 (Received by flhurricane at: 4:54 AM 04.Sep.2011) 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 |
