000 WTPZ42 KNHC 230246 TCDEP2 TROPICAL DEPRESSION SEVENTEEN-E DISCUSSION NUMBER 1 NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL EP172009 800 PM PDT TUE SEP 22 2009 SATELLITE IMAGERY INDICATES THAT THE BROAD AREA OF LOW PRESSURE LOCATED SEVERAL HUNDRED MILES SOUTHWEST OF THE SOUTHERN TIP OF BAJA CALIFORNIA HAS ACQUIRED SUFFICIENT CONVECTION ORGANIZATION TO BE DESIGNATED AS A TROPICAL DEPRESSION...THE SEVENTEENTH OF THE SEASON. THE DEPRESSION IS COMPRISED OF AN ELONGATED AND FAIRLY SHAPELESS MASS OF CENTRAL CONVECTION...DISPLACED NORTHWEST OF THE ESTIMATED CENTER DUE TO SOUTHEASTERLY SHEAR. DVORAK T-NUMBERS ARE T 2.0 FROM BOTH TAFB AND SAB AND SERVE AS THE BASIS FOR SETTING THE ADVISORY INTENSITY AT 30 KT. WITHIN 24 HOURS... SOUTHWESTERLY SHEAR IS EXPECTED TO BEGIN INCREASING AND SHOULD BECOME PROHIBITIVELY STRONG BY 48 HOURS. HOWEVER...PRIOR TO ENCOUNTERING THIS HIGH SHEAR ENVIRONMENT...THE DEPRESSION HAS SOME OPPORTUNITY TO BECOME A TROPICAL STORM. WEAKENING IS THEN FORECAST AFTER 36 HOURS...WITH THE DEPRESSION FORECAST TO BECOME A REMNANT LOW BY 72 HOURS. THE OFFICIAL FORECAST IS IN BEST AGREEMENT WITH THE SHIPS/LGEM GUIDANCE AND DOES NOT CONSIDER THE GFDL/HWRF INTENSITY FORECASTS WHICH CALL FOR THE DEPRESSION TO BECOME A HURRICANE. THESE FORECASTS APPEAR TO BE UNREALISTIC..GIVEN THE STRONG SHEAR FORECAST BY THE GLOBAL MODELS. THERE IS MORE UNCERTAINTY THAN NORMAL IN THE INITIAL MOTION...WHICH IS ESTIMATED AT 320/08. GLOBAL MODELS SHOW A BREAK IN THE SUBTROPICAL RIDGE BETWEEN 115 WEST AND 120 WEST...WHICH SHOULD STEER THE DEPRESSION ON A GENERAL NORTHWESTWARD COURSE FOR THE NEXT 24 HOURS. THEREAFTER...THE STRONG SHEAR FORECAST BY THE GLOBAL MODELS SHOULD CAUSE A DECOUPLING OF THE CYCLONE...WITH THE LOW- LEVEL CENTER EXPECTED TO TURN TOWARD THE WEST AT A REDUCED FORWARD SPEED UNTIL DISSIPATION. FORECAST POSITIONS AND MAX WINDS INITIAL 23/0300Z 15.7N 115.7W 30 KT 12HR VT 23/1200Z 16.4N 116.5W 35 KT 24HR VT 24/0000Z 17.3N 117.5W 40 KT 36HR VT 24/1200Z 17.6N 118.2W 35 KT 48HR VT 25/0000Z 17.7N 119.0W 30 KT 72HR VT 26/0000Z 17.8N 120.5W 20 KT...REMNANT LOW 96HR VT 27/0000Z...DISSIPATED $$ FORECASTER KIMBERLAIN