Evaluation of NCEP Global Ensemble in Predicting Tropical Cyclogenesis Over the East Atlantic: Case studies during August-September 2006

The ability of the NCEP global ensemble forecasting system (GEFS) in predicting tropical cyclogenesis over the Eastern Atlantic Ocean is evaluated with case studies during August-September of 2006. First, we conduct synoptic and statistical analyses to investigate the accuracy of tropical cyclogenesis forecast from NCEP global ensemble. Then the structures of the ensemble spreads of different variables are analyzed to identify the most uncertain factors (e.g., environmental conditions such as wind shear and thermodynamic fields) that may affect the accuracy of the tropical cyclogenesis forecast. Finally, the sensitivity of accuracy of global ensemble forecasts to the sizes of initial perturbations is going to be further evaluated by comparing the ensemble forecasts with high-resolution data obtained from the NASA African Monsoon Multidisciplinary Analyses (NAMMA) field program.