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North American Fire Weather Catalyzed by the Extratropical Transition of Tropical Cyclones


 When tropical cyclones in the western North Pacific turn into midlatitude cyclones, it often perturbs the jet stream, resulting in amplified flow conditions in the north Pacific and various weather extremes in North America. Thus far, however, the complex impacts of extratropical transitioning cyclones (ETCs) on North American fire weather are undocumented. In this study, we group ETCs by the characteristics that are important for their interaction with the jet stream and document the response in North American fire weather, finding that ETCs are consistently associated with enhanced fire weather in North America through amplified pressure gradients and anomalous winds. While the chaotic nature of the ETC and jet stream interaction means that ETCs grouped by similar characteristics and locations can result in varying downstream responses, the composite analysis reveals some areas of consistently enhanced fire weather, including the Pacific Northwest and northern Intermountain West. At a time in which the risk and extent of wildfires in the Western United States is an issue of growing concern, this study represents the first holistic understanding of how ETCs’ downstream perturbations impact fire weather.