An Evaluation of Tropical Cyclone Forecast Skill in the GEFS Reforecast Version 2

The prediction skill of tropical cyclones in the GEFS Reforecast Version 2 was evaluated using different metrics. It was found that the GEFS skillfully captures the seasonal cycle of tropical cyclogenesis over the Atlantic. However, large errors exist on the regional scales in both the week-1 and week-2 reforecasts. In particular, tropical cyclogenesis frequency and track density were significantly under-predicted over the West Atlantic and the Gulf of Mexico but over-predicted over the East Atlantic. Regional biases were also found over the other northern hemispheric basins. Further analyses suggested that such biases can be attributed to the mean state biases in the reforecasts as well as to the biases of the African easterly wave activity over the Atlantic. The impacts of some large-scale climate factors on the prediction skills were also investigated.