000 WTNT41 KNHC 280855 TCDAT1 TROPICAL DEPRESSION SIXTEEN DISCUSSION NUMBER 2 NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL AL162007 500 AM EDT SUN OCT 28 2007 THE CENTER OF THE DEPRESSION IS DIFFICULT TO IDENTIFY ON INFRARED OR NIGHT-VIS IMAGERY. RECENT MICROWAVE PASSES ALSO ARE NOT CONCLUSIVE...BUT SUGGEST THAT THE DEPRESSION IS CONTINUING ON ITS PREVIOUS TRACK...WITH AN INITIAL MOTION ESTIMATE OF 300/6. DEEP CONVECTION NEAR THE CENTER LACKS ANY APPRECIABLE BANDING...AND A RECENT ASCAT PASS DOES NOT INDICATE THAT ANY STRENGTHENING HAS OCCURRED. WITH AN UPPER-LEVEL LOW IMPARTING WESTERLY SHEAR OVER THE CYCLONE...THE ENVIRONMENT DOES NOT FAVOR MUCH DEVELOPMENT IN THE SHORT TERM. GLOBAL MODELS SUGGEST THAT THE UPPER LOW WILL WASH OUT IN A COUPLE OF DAYS...LEAVING THE CYCLONE UNDER A LESS HOSTILE UPPER PATTERN...BUT THE ENVIRONMENT NEVER APPEARS TO BE IDEAL FOR DEVELOPMENT. IN ADDITION...THERE IS AMPLE OPPORTUNITY FOR LAND INTERACTIONS OVER THE NEXT FEW DAYS THAT WOULD HINDER STRENGTHENING. THE GFDL AND HWRF INTENSITY FORECASTS...WHICH SUGGEST A MORE VERTICALLY-CONNECTED CYCLONE THAN APPEARS TO EXIST...ARE LARGELY BEING DISCOUNTED. THE OFFICIAL FORECAST IS IN GOOD AGREEMENT WITH THE LGEM. TRACK FORECASTING OF WEAK SYSTEMS IN SHEARED ENVIRONMENTS IS PARTICULARLY CHALLENGING...AND THE AVAILABLE MODEL GUIDANCE REFLECTS THIS UNCERTAINTY. THE PRIMARY SYNOPTIC PLAYERS ARE THE UPPER-LOW ALREADY MENTIONED...A MID-LEVEL RIDGE OVER THE SOUTHWESTERN ATLANTIC...A BROAD LOW-LEVEL CYCLONIC ENVELOPE SURROUNDING THE DEPRESSION...AND A MID- TO UPPER-LEVEL SHORTWAVE TROUGH FORECAST TO MOVE INTO THE SOUTHEASTERN UNITED STATES IN ABOUT FOUR DAYS. THE GFDL AND HWRF LIE ON THE EASTERN EDGE OF THE GUIDANCE ENVELOPE...TAKING THE CYCLONE ACROSS HISPANIOLA AND THROUGH THE CENTRAL BAHAMAS IN 2-3 DAYS. THIS APPEARS TO RESULT FROM AN OVERLY STRONG INTERACTION WITH THE UPPER LOW. ANOTHER SCENARIO IS FOR THE DEPRESSION TO TURN TEMPORARILY TO THE NORTHWEST IN RESPONSE TO THE UPPER-LOW...BUT THEN BEND BACK TO THE WEST-NORTHWEST IN A COUPLE DAYS AROUND THE BROAD LOW-LEVEL GYRE...BEFORE BEING DEFLECTED NORTHEASTWARD WHEN THE SHORT WAVE ARRIVES ON DAYS 4-5. THIS IS THE SOLUTION OF THE UKMET. ON THE LEFT SIDE OF THE GUIDANCE ENVELOPE ARE THE BAM MODELS AND THE GFS...WHICH TAKE A RELATIVELY WEAK AND ILL-DEFINED LOW WEST-NORTHWESTWARD UNTIL THE MID-LATITUDE SHORT WAVE ARRIVES AND SLOWLY RECURVES THE CYCLONE. THIS IS THE SOLUTION FAVORED BY THE OFFICIAL FORECAST. IT IS WORTH REITERATING THAT THE UNCERTAINTY LEVEL IS HIGH. FORECAST POSITIONS AND MAX WINDS INITIAL 28/0900Z 16.2N 72.1W 30 KT 12HR VT 28/1800Z 17.0N 73.2W 30 KT 24HR VT 29/0600Z 17.9N 74.6W 35 KT 36HR VT 29/1800Z 18.9N 76.3W 35 KT 48HR VT 30/0600Z 19.7N 77.7W 40 KT 72HR VT 31/0600Z 21.5N 80.0W 50 KT 96HR VT 01/0600Z 23.0N 79.0W 40 KT 120HR VT 02/0600Z 25.0N 77.0W 45 KT...EXTRATROPICAL $$ FORECASTER FRANKLIN