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| #454889 (Received by flhurricane at: 4:55 AM 30.Aug.2011) TCDAT2 TROPICAL STORM KATIA DISCUSSION NUMBER 5 NWS NATIONAL HURRICANE CENTER MIAMI FL AL122011 500 AM AST TUE AUG 30 2011 THE CONVECTIVE PATTERN OF THE CYCLONE HAS IMPROVED OVERNIGHT...WITH A LARGE AREA OF COLD CLOUD TOPS NOW SITUATED TO THE WEST AND SOUTHWEST OF THE ESTIMATED CENTER LOCATION. THE 06Z DVORAK INTENSITY ESTIMATES FROM TAFB AND SAB WERE BOTH 2.5/35 KT...AND ON THIS BASIS THE CYCLONE IS UPGRADED TO A TROPICAL STORM. THE STRUCTURE OF KATIA IS CONSISTENT WITH THE 15-20 KT OF EAST-NORTHEASTERLY SHEAR OVER THE CYCLONE ANALYZED BY THE SHIPS MODEL AND UW-CIMSS. THIS SHEAR SHOULD DECREASE IN THE NEXT 12 HOURS OR SO...AND AFTER THAT TIME STEADY INTENSIFICATION SHOULD COMMENCE AS THE CYCLONE MOVES OVER PROGRESSIVELY HIGHER OCEAN HEAT CONTENT. MOST OF THE INTENSITY GUIDANCE HAS TRENDED UPWARD THIS CYCLE...AND THE OFFICIAL FORECAST HAS AS WELL. KATIA IS EXPECTED TO BE NEAR HURRICANE STRENGTH WITHIN 36 TO 48 HOURS WITH CONTINUED STRENGTHENING TO NEAR MAJOR HURRICANE STATUS BY THE END OF THE PERIOD. THE NHC FORECAST IS CLOSE TO THE MULTI-MODEL CONSENSUS THAT INCLUDES THE HFIP INTENSITY AIDS. A TIMELY AMSR-E PASS FROM 0326Z WAS HELPFUL IN LOCATING THE CENTER ON THE EASTERN EDGE OF THE DEEP CONVECTION...WHICH WAS A BIT NORTH OF PREVIOUS ESTIMATES. THE INITIAL MOTION ESTIMATE IS 290/15...AS KATIA CONTINUES TO BE STEERED WEST-NORTHWESTWARD BY THE SUBTROPICAL RIDGE TO ITS NORTH. THE MODEL GUIDANCE IS IN GOOD AGREEMENT ON A CONTINUATION OF THIS GENERAL MOTION THROUGH THE PERIOD AS THE MID-LEVEL RIDGE BUILDS WESTWARD TO THE NORTH OF THE CYCLONE. AT DAYS 4 AND 5...THE WESTERN EDGE OF THE RIDGE BEGINS TO WEAKEN AS A MID-LEVEL TROUGH AMPLIFIES OVER THE WESTERN ATLANTIC...WHICH SHOULD RESULT IN SOME DECREASE IN FORWARD SPEED. THE TRACK GUIDANCE REMAINS TIGHTLY CLUSTERED BUT THERE ARE SOME FORWARD SPEED DIFFERENCES...WITH THE UKMET AND GFDL MODELS ON THE FAST SIDE OF THE GUIDANCE AND THE GFS CONTINUING TO BE A SLOW OUTLIER. FOR THIS CYCLE THE MODELS HAVE TRENDED FASTER DURING THE FIRST 72 HOURS... AND SO HAS THE OFFICIAL FORECAST. OTHERWISE...THE NHC FORECAST IS VERY CLOSE TO THE PREVIOUS ONE AND LIES NEAR OR A LITTLE TO THE RIGHT OF THE TVCA MULTI-MODEL CONSENSUS THROUGH THE PERIOD. FORECAST POSITIONS AND MAX WINDS INIT 30/0900Z 11.8N 31.7W 35 KT 40 MPH 12H 30/1800Z 12.5N 33.7W 40 KT 45 MPH 24H 31/0600Z 13.5N 36.8W 50 KT 60 MPH 36H 31/1800Z 14.4N 40.2W 60 KT 70 MPH 48H 01/0600Z 15.3N 43.7W 70 KT 80 MPH 72H 02/0600Z 17.0N 49.5W 80 KT 90 MPH 96H 03/0600Z 18.5N 54.0W 90 KT 105 MPH 120H 04/0600Z 20.5N 58.0W 100 KT 115 MPH $$ FORECASTER BRENNAN |
