The Global Ensemble Forecast System (GEFS v11) will be upgraded in early December 2015 with following main changes: 1) Increasing horizontal and vertical resolutions; 2) Latest GFS model physics with semi-Lagrangian integration of advection instead of Euler integration; 3) New initial analysis from hybrid GSI and initial perturbations from EnKF 6-hour forecast. The GEFS (v11) has best performance for large-scale circulation, summer precipitation forecast, surface temperature forecast, extreme weather event and TC track forecast overall. However, it degrades TC track forecast of day-6 and day-7 for Atlantic and East Pacific basins, and increases TC intensity forecast error (or weaker TC intensity) as well.
The study focuses on the extend-range (beyond day-5) TC track forecast for Atlantic basin. The four-way experiments have been designed for selected Hurricane cases those include: 1) Operational GEFS (BV-ETR initial perturbations and GEFSv10); 2) Parallel GEFS (EnKF-F06 initial perturbations and GEFSv11); 3) Experimental GEFS-1 (BV-ETR initial perturbations and GEFSv11); and 4) Experimental GEFS-2 (EnKF-F06 initial perturbations and GEFSv10). Through the case study, we could identify the differences those are relatively contributed by initial condition/perturbations or numerical modeling. Meanwhile, an analysis of other atmospheric variables, such as lower level winds, surface pressure, water vapors and et. al. around tropical region, will help us to understand the impact from the changes of initial condition, model physics and numerical schemes.
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