A Climatology of Multiple Tropical Cyclone Events

Abstract:

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 active 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 the prior global climatology of TC activity may not be representative of multiple TC events. 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. With regards to the large-scale factors forcing multiple TC events, non-multiple TC event frequency does not exhibit sensitivity to either ENSO or MJO, while multiple TC events exhibit significant sensitivity to ENSO in the EPAC and NATL and MJO phase in the EPAC and WPAC. Composites of EPAC multiple TC events suggest significantly stronger basin-scale environmental preconditioning associated with the convectively active MJO several weeks prior to multiple TC events creating a more favorable environment for TC genesis compared to non-multiple TC events. In their totality, these results suggest remarkable similarity in the climatological multiple TC event frequency and location among basins, while suggesting that multiple TC events may be predictable weeks ahead of time given the occurrence of basin-scale environmental preconditioning prior to these events.