The Extratropical Transition of Tropical Cyclones: Structural Characteristics, Downstream Impacts, and Forecast Challenges

Abstract

The process of extratropical transition (ET) occurs when a tropical cyclone moves poleward into the midlatitudes. During ET a decaying tropical cyclone frequently re-intensifies as an intense extratropical cyclone, which may produce intense rainfall, strong winds and hazardous seas. Changes in the structure of decaying tropical cyclone to an extratropical cyclone involve interactions among a number of complex physical processes. Furthermore variability among the interactions contributes to decreased predictability of the ET process. The variability in ET processes is related to the interaction between the decaying tropical cyclone and the midlatitude circulation into which it is moving. One of the important impacts of the ET of a tropical cyclone has been recently recognized as the influence on the multi-scale dynamics associated with the midlatitude circulation far downstream of the ET event. The downstream impacts may be related to a variety of physical processes associated with the decaying TC and the midlatitude characteristics in which the ET is occurring. In this review, the classification of ET types, important physical characteristics, interactions with the midlatitude circulation, downstream impacts, and predictability are discussed.