Characteristics of the extratropical transition of tropical cyclones on different tracks in the western North Pacific

As one of the most destructive types of natural disaster, tropical cyclones have long been a key focus in disaster prevention and mitigation efforts. However, when tropical cyclones migrate into the mid-to-high latitudes, they gradually lose their tropical cyclone characteristics, and transform into extratropical cyclones. People’s vigilance tends to decrease, believing that such storms pose less of a threat. In fact, this transformation expands the impact range of the storm, while combining the characteristics of tropical and extratropical cyclones. It leads to heavy rainfall, huge waves and strong winds, causing more serious damage than a single type of cyclone.

 

Currently, our level of understanding of the activity characteristics and transformation mechanism of these “extratropical transition tropical cyclones” (ETCs) in the western North Pacific remains incomplete, which poses significant challenges to disaster warning and numerical forecasting.

 

Recently, Associate Professor Lei Chen, from the Department of Atmospheric Science, School of Environmental Studies, China University of Geosciences (Wuhan), with her research team, conducted a classification of 386 ETCs that occurred in the western North Pacific from 1979 to 2022, into four clusters according to their track patterns: recurving ETCs, westward ETCs, northwestward ETCs, and abnormal track ETCs. In their study, published in Atmospheric and Oceanic Science Letters under the title “Climatological characteristics of the extratropical transition of tropical cyclones along different tracks in the western North Pacific (1979–2022)”, they reveal the transition characteristics and mechanisms of these four clusters of ETCs.

 

Results showed that the four clusters of ETCs possessed significant differences in transition duration, location, and mechanism. Recurving ETCs predominantly underwent transition during their track recurvature from northwest to northeast. Of the westward ETCs, 63.7% completed the transformation process rapidly after landing. Northwestward ETCs typically underwent transition in the baroclinic zone between 15°N and 20°N, characterized by the longest duration and slowest transition speed. Abnormal track ETCs mainly completed their transition over high-latitude oceans.

 

The transition process is closely related to the position and extent of the western Pacific subtropical high. “When the subtropical high extends westward, the frequency of ETCs increases, and the frequency decreases when it retreats eastward. Except for the westward ETCs, which are dominated by surface friction effects, the other clusters of ETCs mainly complete the transition in the northwest baroclinic zone of the subtropical high, and are affected by ocean thermal forcing or cold-air invasion,” concludes the corresponding author, Lei Chen.

---

---