Evaluation of Tropical Cyclogenesis Forecasts in Different Synoptic-scale Environments

The prediction skills of the tropical cyclogenesis over the Atlantic are examined using the GEFS Reforecast for different genesis pathways. Among the five genesis pathways identified by McTaggart-Cowan et al., the strong tropical transition pathway, in which the upper-level forcing plays an important role in genesis, has the lowest probability of detection (POD), while the low-level baroclinic pathway has the highest probability of detection but the false alarm rate is also much higher. The week-1 reforecasts show high prediction skills when the model is initialized at phase 2 or phase 3 of the MJO (based on the Wheeler-Hendon index). Such sensitivity, however, disappears as the MJO signals attenuate in the week-2 reforecasts. The large-scale circulation biases related to the tropical cyclone forecast errors are also investigated.