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#635481 (Received by flhurricane at: 4:41 AM 30.Sep.2013) TCDAT1 TROPICAL DEPRESSION ELEVEN DISCUSSION NUMBER 6 NWS NATIONAL HURRICANE CENTER MIAMI FL AL112013 500 AM AST MON SEP 30 2013 THE CONVECTIVE CLOUD SHIELD REMAINS SHEARED NORTHEAST THROUGH SOUTHEAST OF THE CENTER. THERE HAS BEEN A NOTICEABLE INCREASE IN LIGHTNING ACTIVITY DURING THE PAST COUPLE OF HOURS...WHICH IS OFTEN INDICATIVE OF INCREASING VERTICAL WIND SHEAR. SATELLITE INTENSITY ESTIMATES REMAIN T2.0/30 KT FROM TAFB AND SAB...ALTHOUGH SAB REPORTED A DATA T-NUMBER OF T2.5/35 KT. ADT VALUES ARE T2.8/41 KT AND A 02032Z OSCAT PASS CONTAINED SOME RAIN-FREE 30-35 KT WIND VECTORS IN THE EASTERN QUADRANT...SUGGESTING THAT THE CYCLONE IS VERY NEAR TROPICAL STORM STRENGTH. HOWEVER...GIVEN THE HISTORY OF THIS SYSTEM GOING THROUGH SPORADIC CONVECTIVE BURSTING PHASES...THE INTENSITY IS BEING MAINTAINED AT 30 KT WITH THE GUST DIFFERENTIAL BEING INCREASED TO 45 KT UNTIL A MORE PERSISTENT CONVECTIVE PATTERN BECOMES ESTABLISHED. THE DEPRESSION HAS TURNED EASTWARD AND HAS SLOWED DOWN...AND THE INITIAL MOTION IS NOW 090/04 KT. THERE IS NO SIGNIFICANT CHANGE TO THE PREVIOUS FORECAST TRACK OR REASONING. THE NHC MODEL GUIDANCE REMAINS IN GOOD AGREEMENT ON THE CYCLONE MAKING A SLOW CLOCKWISE LOOP OVER THE NEXT 48-72 HOURS BEFORE ACCELERATING OFF TO THE NORTHEAST OVER THE OPEN CENTRAL ATLANTIC AHEAD OF A BROAD MID-/UPPER-LEVEL TROUGH ON DAYS 4 AND 5. THE FORECAST TRACK IS SIMILAR TO THE PREVIOUS ADVISORY TRACK...AND LIES TO THE RIGHT OF THE CONSENSUS MODEL TVCA AT 72 HOURS AND BEYOND DUE TO A SIGNIFICANT WESTWARD BIAS CAUSED BY THE HWRF MODEL. MOST OF THE INTENSITY MODEL GUIDANCE...AS WELL AS THE GLOBAL MODELS...INDICATE THAT THE CYCLONE WILL REMAIN IN MODERATE SHEAR CONDITIONS THROUGHOUT THE ENTIRE FORECAST CYCLE. THE EXCEPTION IS BETWEEN 48 TO 72 HOURS WHEN THE SHEAR COULD LESSEN SOMEWHAT AS THE CYCLONE BRIEFLY MOVES UNDERNEATH A NARROW UPPER-LEVEL RIDGE AS A TROUGH BYPASSES THE SYSTEM TO THE NORTHEAST. THIS COULD ALLOW FOR MORE STRENGTHENING BETWEEN THOSE TWO FORECAST TIME PERIODS BEFORE SOUTHWESTERLY SHEAR BEGINS TO INCREASE AGAIN AT AROUND 72 HOURS AND BEYOND. THE INTENSITY FORECAST IS CLOSE TO THE ICON CONSENSUS MODEL...AND REMAINS NEAR THE LOW END OF THE GUIDANCE SUITE. FORECAST POSITIONS AND MAX WINDS INIT 30/0900Z 26.9N 46.7W 30 KT 35 MPH 12H 30/1800Z 26.9N 46.1W 35 KT 40 MPH 24H 01/0600Z 26.6N 46.0W 35 KT 40 MPH 36H 01/1800Z 26.4N 46.3W 40 KT 45 MPH 48H 02/0600Z 26.3N 47.2W 40 KT 45 MPH 72H 03/0600Z 27.4N 49.0W 40 KT 45 MPH 96H 04/0600Z 29.5N 48.2W 35 KT 40 MPH 120H 05/0600Z 32.0N 44.7W 35 KT 40 MPH $$ FORECASTER STEWART |