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#372925 (Received by flhurricane at: 11:49 AM 01.Sep.2010) TCDAT4 TROPICAL DEPRESSION NINE DISCUSSION NUMBER 1 NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL AL092010 1100 AM AST WED SEP 01 2010 THE VIGOROUS TROPICAL WAVE IN THE EASTERN TROPICAL ATLANTIC HAS BECOME BETTER ORGANIZED WITH DEEP CONVECTION WRAPPING ALMOST HALF WAY AROUND THE VORTEX. CONSEQUENTLY...DVORAK INTENSITY ESTIMATES FROM TAFB AND SAB SUPPORT INITIATING ADVISORIES ON THIS SYSTEM AS A TROPICAL DEPRESSION. AN ASCAT PASS AT 1126Z ALONG THE EDGE OF THE CYCLONE INDICATED WINDS OF 25-30 KT. THE INITIAL INTENSITY IS SET AT 30 KT. THE MOTION OF THE DEPRESSION IS 275 DEGREES AT 15 KT AS IT IS BEING STEERED PRIMARILY BY A LARGE DEEP-LAYER SUBTROPICAL RIDGE TO ITS NORTH. AS A STRONG MID-LATITUDE SHORT WAVE MOVES ACROSS THE NORTH ATLANTIC...THE RIDGE WEAKENS SOME DURING THE NEXT TWO TO THREE DAYS. THIS SHOULD RESULT IN A SLOWING OF THE CYCLONE AND A SLIGHT TURN TOWARD THE WEST-NORTHWEST. BY DAYS FOUR AND FIVE...THE SUBTROPICAL RIDGE RESTRENGTHENS AND THE DEPRESSION SHOULD CORRESPONDINGLY ACCELERATE. THE GLOBAL MODELS ARE HAVING DIFFICULTY DISTINGUISHING THE CYCLONE FROM THE PRONOUNCED MONSOON TROUGH IN THE EASTERN ATLANTIC. THE FORECAST TRACK IS A BLEND OF THE AVAILABLE GLOBAL MODELS...THE UKMET AND CANADIAN...AND THE GFDL AND HWRF HURRICANE MODELS AND IS CLOSEST TO THE BAM-MEDIUM MODEL. THE 12Z GLOBAL MODEL GUIDANCE SHOULD PROVIDE A BETTER TRACK PREDICTION SINCE THEY WILL HOPEFULLY HAVE A MORE REALISTIC HANDLE ON THE INITIAL CONDITIONS OF THE DEPRESSION. THE INTENSITY FORECAST...AS USUAL...IS QUITE UNCERTAIN. WHILE THE DEPRESSION WILL BE TRAVERSING OVER VERY WARM WATERS...THE VERTICAL SHEAR...ESPECIALLY THE MID-LEVEL CONTRIBUTION...IS MODERATE TO STRONG. ADDITIONALLY...A LARGE OUTBREAK OF THE SAHARAN AIR LAYER IS SITUATED JUST NORTH AND WEST OF THE DEPRESSION...WHICH MAY INHIBIT SOME OF THE DEEP CONVECTION IN THE CORE OF THE SYSTEM. THE FORECAST INTENSITY ONLY CALLS FOR GRADUALLY SPINNING THE CYCLONE UP AND IS CLOSE TO THE FOUR-MODEL INTENSITY CONSENSUS. IT IS WORTH NOTING THAT SOME OF THE GLOBAL MODELS...IN PARTICULAR THE GFS AND NOGAPS DO NOT EVEN ACKNOWLEDGE THAT THE CYCLONE EXISTS NOW OR IN THE NEAR FUTURE. HOWEVER...A QUICK DECAY OF THIS SYSTEM DOES NOT APPEAR TO BE LIKELY. FORECAST POSITIONS AND MAX WINDS INITIAL 01/1500Z 12.4N 35.8W 30 KT 12HR VT 02/0000Z 12.6N 37.8W 35 KT 24HR VT 02/1200Z 13.0N 39.8W 35 KT 36HR VT 03/0000Z 13.5N 41.4W 40 KT 48HR VT 03/1200Z 14.0N 42.8W 40 KT 72HR VT 04/1200Z 15.0N 45.0W 40 KT 96HR VT 05/1200Z 16.0N 49.0W 45 KT 120HR VT 06/1200Z 17.0N 53.0W 50 KT $$ FORECASTER LANDSEA/BLAKE |