ZCZC MIATCDAT1 ALL TTAA00 KNHC DDHHMM TROPICAL DEPRESSION SIXTEEN DISCUSSION NUMBER 3 NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL AL162010 1100 PM EDT TUE SEP 28 2010 TROPICAL DEPRESSION SIXTEEN CONTINUES TO HAVE A STRUCTURE MORE CHARACTERISTIC OF A WESTERN NORTH PACIFIC/NORTH INDIAN OCEAN MONSOON DEPRESSION. SURFACE OBSERVATIONS CONTINUE TO INDICATE WINDS OF 20 KT OR LESS OVER AN AREA ENCOMPASSING 100 N MI IN DIAMETER FROM THE CENTER...AND THAT THE STRONGEST WINDS AND CONVECTION ARE 250-300 N MI AWAY FROM THE CENTER IN THE SOUTHEASTERN QUADRANT. AN EARLIER AIR FORCE RESERVE HURRICANE HUNTER MISSION IN THIS AREA FOUND FLIGHT-LEVEL WINDS SUPPORTING AN INITIAL INTENSITY OF 30 KT. SURFACE OBSERVATIONS INDICATE THAT THE CENTRAL PRESSURE IS NEAR 997 MB. THERE ARE MULTIPLE LOW-LEVEL CLOUD SWIRLS PRESENT...AND THE CENTER APPEARS TO RE-FORM FROM TIME TO TIME. THE INITIAL MOTION OF 035/7 IS THUS A BIT UNCERTAIN. OTHER THAN THAT...THERE IS NO CHANGE IN THE FORECAST PHILOSOPHY FROM THE PREVIOUS ADVISORY...AND ONLY MINOR CHANGES TO THE FORECAST TRACK. A COMBINATION OF A DEEP-LAYER TROUGH OVER THE SOUTHEASTERN UNITED STATES AND EASTERN GULF OF MEXICO AND A LOW/MID-LEVEL RIDGE OVER THE WESTERN ATLANTIC SHOULD STEER THE CYCLONE NORTH-NORTHEASTWARD WITH ACCELERATION FOR THE NEXT 12-24 HOURS...FOLLOWED BY A QUICK NORTHWARD MOTION. THERE IS SOME SPREAD IN BOTH THE SPEED AND DIRECTION OF MOTION BY 48 HR. THE GFS... GFDL...AND HWRF ARE MUCH FASTER AND TO THE LEFT OF THE REST OF THE GUIDANCE...WHILE THE NOGAPS...GFDN...AND GFS ENSEMBLE MEAN ARE SLOWER AND TO THE RIGHT. THESE DIFFERENCES LIKELY RESULT FROM THE MODEL HANDLING OF THE DEPRESSION INTERACTING WITH A DEVELOPING BAROCLINIC LOW OVER THE EASTERN UNITED STATES. THE NEW FORECAST TRACK IS DOWN THE MIDDLE OF THE GUIDANCE ENVELOPE CLOSE TO THE CONSENSUS MODELS. THE DEPRESSION IS CURRENTLY IN AN ENVIRONMENT OF 15 KT OF SOUTHWESTERLY VERTICAL WIND SHEAR...WHICH THE LARGE-SCALE MODELS FORECAST TO INCREASE DURING THE NEXT 12-24 HR. THUS...NEITHER THE ENVIRONMENT NOR THE CURRENT STRUCTURE ARE CONDUCIVE FOR SIGNIFICANT STRENGTHENING. THE INTENSITY FORECAST IS THE SAME AS IN THE PREVIOUS ADVISORY...WITH MODEST STRENGTHENING ALONG THE LINES OF THE SHIPS AND LGEM MODELS. EXTRATROPICAL TRANSITION IS EXPECTED TO BEGIN IN ABOUT 24 HR OR SO AND BE COMPLETE BY 36-48 HR. THE CYCLONE IS FORECAST TO BE ABSORBED BY THE EASTERN U. S. BAROCLINIC LOW AFTER 48 HR...AS FORECAST BY MOST OF THE DYNAMICAL GUIDANCE. UNLESS THE STRUCTURE CHANGES RADICALLY IN THE NEXT 12-24 HOURS...IT IS LIKELY THAT THERE WILL CONTINUE TO BE A LARGE AREA OF LIGHT WINDS NEAR THE CENTER. THE STRONGEST WINDS SHOULD OCCUR IN AREAS WELL TO THE EAST OF THE FORECAST TRACK. FORECAST POSITIONS AND MAX WINDS INITIAL 29/0300Z 21.9N 81.9W 30 KT 12HR VT 29/1200Z 23.3N 81.2W 35 KT 24HR VT 30/0000Z 26.3N 80.2W 40 KT 36HR VT 30/1200Z 30.6N 79.3W 40 KT...POST-TROP/EXTRATROP 48HR VT 01/0000Z 36.3N 78.0W 35 KT...POST-TROP/EXTRATROP 72HR VT 02/0000Z...ABSORBED BY EXTRATROPICAL LOW $$ FORECASTER BEVEN NNNN
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