A Climatology of Indirect Tropical Cyclone Interactions in the Atlantic Basin

While it is understood that a recurving tropical cyclone which interacts with the midlatitude flow can cause large downstream mid-latitude forecast errors, it is much less understood how such events affect the predictability of a downstream tropical cyclone. For this study, an indirect tropical cyclone interaction is defined as one in which an initial tropical cyclone perturbs the downstream, mid-latitude waveguide within one synoptic-scale wavelength of a subsequent tropical cyclone. To achieve a better understanding of the mechanics behind such interactions, a climatology and composite analysis is generated for all indirect interactions occurring between two (or more) tropical and/or subtropical cyclones in the Atlantic Basin from 2000-2017 in the HURDAT2 dataset. A metric for the interaction of a tropical cyclone with the mid-latitude flow is used to identify indirect interaction events and to ascribe an initial interaction start time and location. Utilizing the interaction metric and the Climate Forecast System Reanalysis, a climatology is obtained, from which composites are built. Statistical pattern identification techniques are then used to identify distinct modes of indirect interaction in the full composite. Future research will involve numerical simulations for particular cases to test the extent to which the initial tropical cyclone impacts the mid-latitude waveguide, as well as ensemble-based studies to test the impacted tropical cyclone’s evolution and predictability.