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| #456054 (Received by flhurricane at: 4:52 PM 03.Sep.2011) 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 |
