Local Energetics of Extratropical Transition: A Case Study of Typhoon Hagibis (2019)

Abstract Tropical cyclones (TCs) moving into the midlatitudes often undergo notable structural changes as they transition into extratropical cyclones (ETCs). This transition, known as the extratropical transition (ET), results from interactions between the TC and the midlatitude baroclinic environment. To elucidate the dynamical processes underlying ET, this study proposes a cyclone-following local energetics framework and applies it to TC Hagibis (2019) in the western North Pacific. The energy cycle intensifies during the ET phase, with its spatial structure becoming markedly asymmetric relative to that in the TC phase. In both the TC and ET phases, eddy available potential energy increases as its generation and energy conversion from background flow dominate over the baroclinic energy conversion. During ET, enhanced diabatic heating, warm temperature anomalies, and vertical motion appe…