A Climatology of Multiple Tropical Cyclone Events

Prior seminal research has provided a global climatology of tropical cyclones (TCs) and the large-scale environmental factors that control TC activity. Subsequent research has shown that TC activity frequently clusters in two-to-three week periods with a substantial percentage of TCs existing simultaneously within the same basin (i.e., multiple TC events). However, previous research on a limited subset of multiple TC events suggests that climatology of multiple TC events may differ from prior climatologies of TC activity. Building upon prior work, the present study examines the climatological frequency and location of multiple TC events and the large-scale factors responsible for their occurrence in the North Atlantic (NATL), eastern North Pacific (EPAC), and western North Pacific (WPAC).

In the present study, multiple TC events are defined as tropical cyclogenesis events occurring in the presence of at least one preexisting TC, while non-multiple TC events are defined as TC genesis events occurring in the absence of preexisting TCs. The analysis reveals that multiple TC events constitute a substantial fraction of all TC genesis events in the NATL (24%), EPAC (45%), and WPAC (33%). Moreover, a substantial fraction of preexisting TCs in the NATL (30%), EPAC (40%), and WPAC (23%) are clustered 1000–3000 km west of the TC genesis event during multiple TC events. Reanalysis-based composites suggest that the large-scale environment of EPAC multiple TC events is characterized by the eastward propagation into the EPAC of basin-scale enhanced convection and near-equatorial lower-and-upper-tropospheric zonal wind anomalies associated with the Madden–Julian Oscillation (MJO). These results together with the absence of significant large-scale environmental anomalies in the EPAC non-multiple TC events composites suggest that the MJO may be important in creating a favorable environment over a sufficiently large area for multiple TCs to simultaneously exist. In their totality, these results suggest remarkable similarity in multiple TC event characteristics among basins, while suggesting that multiple TC events may be predictable weeks ahead of time due to potential importance of the MJO during these events.