North American fire weather catalyzed by the extratropical transition of tropical cyclones

When tropical cyclones in the western North Pacific transition 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 climatological impacts of extratropical transitioning cyclones (ETCs) on North American fire weather are mostly 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. We find that ETCs are consistently associated with broad swaths of suppressed fire weather along with smaller areas of enhanced fire weather in North America, mostly through anomalous upper-level circulation and near-surface temperatures. 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 altered fire weather for ETCs which recurve at certain longitudinal ranges, 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.