Predictability of Tropical Cyclone Formation for Different Genesis Pathways

The extended-range forecasts of tropical cyclone activity at intraseasonal time scale have been improved in recent years, which can be at least partly attributed to the improvement of dynamical models in predicting the Madden Julian Oscillation (MJO). The predictability of the tropical cyclogenesis over the Atlantic are examined using the 28-year (1985-2012) 2nd-generation GEFS Reforecast (GEFS/R) and three-year ECMWF ensemble forecasts for different genesis pathways. It is found that the thermodynamically controlled genesis pathways are better predicted than the dynamically controlled pathways. Strong tropical transition (TT) pathway has the most limited predictability. Geographically, models are more skillful in predicting the tropical cyclogenesis over the eastern Main Development Region (MDR; east of 45ºW) but with a high false alarm rate. The wave-number frequency diagram of 200 hPa zonal wind of the GEFS/R shows a rapid attenuation of the MJO signals with the forecast lead time, which may affect the prediction skill of the GEFS model. The impacts of some large-scale climate factors on the predictability of tropical cyclone activity are also examined.