Evaluation of causes of large 96-h and 120-h track errors in the western North Pacific

Previous experience at the Joint Typhoon Warning Center (JTWC) has demonstrated that consensus track forecasting works best when four or more skillful dynamical models tracks are available. Whereas JTWC has ten track forecasts to 72 h, at longer intervals only four forecasts are available. A consensus that includes one or more erroneous tracks can then seriously degrade the 96-h and 120-h forecasts. Proper identification and removal of the track forecast displaying an error mechanism could form a selective consensus that will be more accurate than the non-selective consensus. Kehoe (2005, M.S. thesis, NPS) examined all large (>400 n mi at 96 h, and >500 n mi at 120 h) Navy Operational Global Atmospheric Prediction System (NOGAPS) and U.S. Navy version of the Geophysical Fluid Dynamics Laboratory Model (GFDN) tropical cyclone track forecast errors in the western North Pacific during the 2004 typhoon season. Error mechanisms are described by conceptual models that are related to known tropical cyclone motion processes being misrepresented in the dynamical fields. Large error cases occurring due to tropical influences were dominated by the excessive direct cyclone interaction (E-DCI) mechanism. Large error cases due to midlatitude influences were dominated by midlatitude system evolutions to include both excessive and insufficient midlatitude cyclogenesis (E-MCG and I-MCG), excessive midlatitude cyclolysis (E-MCL), and excessive midlatitude anticyclogenesis (I-MAG.) In this research, large errors during the 2005 typhoon season by the NOGAPS, GFDN, United Kingdom Met Office (UKMO) and NCEP Global Forecast System (GFS) are examined. Characteristics and symptoms of the erroneous forecast tracks and model fields are documented and illustrative case studies are presented.