What controls the interannual variation of tropical cyclone genesis frequency over Bay of Bengal in the post-monsoon peak season?

Tropical cyclone (TC) over Bay of Bengal (BoB) during its climatologic maximum peak season (October-November, post-monsoon season) exhibits a significant interannual variation between a negative Indian Ocean dipole (NIOD) and a positive IOD (PIOD) phase but not between El Nino and La Nina phase. Diagnosis of observational data reveals that the most important parameter that determines the interannual variation of BoB TC is the interaction between the mid-tropospheric relative humidity and the long-term mean states of absolute vorticity, vertical wind shear, and potential intensity. The change of mid-tropospheric moisture is primarily determined by vertical advection associated with low-level vorticity anomalies during IOD.