Typhoons are one of the most destructive weather systems with potentially serious impacts on human life, economics, social systems, and the environment. In particular, typhoons Jebi (2018), Faxai (2019), and Hagibis (2019), which made landfall in Japan, caused serious natural disasters in various areas of Japan and resulted in the record-breaking amount of insurance claims paid due to strong winds, torrential rainfalls, high waves, and storm surge. It is of great scientific interest that the causes and processes are clarified particularly on strong winds of Jebi and Faxai and heavy rainfall of Hagibis.
Regarding the prediction of typhoon intensity in 2018-2019, rapid intensification and weakening of typhoons remain challenging scientific topics. The interactions between typhoon Trami (2018) and the ocean and between typhoon Jongdari (2018) and the upper-tropospheric cold-core low are interesting topics in understanding the effect on the typhoon track predictions. Furthermore, the effect of global warming on these meteorological events in the future are also topics of great interest in addition to the effect on climatological typhoon activity in the western North Pacific.
In this special edition jointly coordinated with Journal of the Meteorological Society of Japan, we publish papers on all aspects of typhoons in 2018-2019, such as formation, movement, intensification, weakening, structure change, strong wind, heavy rainfall, high wave, storm surge, and the interaction with terrain, ocean, or midlatitude systems. We also publish papers on studies on the linkage between typhoons and climate processes that include both natural and anthropogenic origin and on the effect of global warming on meteorological events associated with typhoons in 2018-2019.
One of the remarkable environmental characteristics of tropical cyclone (TC) Hagibis (2019) was the positive sea surface temperature (SST) anomaly observed in the western North Pacific Ocean. In this study, an ensemble-based sensitivity experiment was conducted with a nonhydrostatic model, focusing on the impact of SST on TC motion. The TC with the analyzed SST (warm run) moved faster near mainland Japan than with the lowered SST (cold run), as the TC in the warm run was embedded earlier in the mid-latitude westerly jet located to the north than that in the cold run. The TC displacement was consistent with the large decrease of geopotential height at 500-hPa (Z500) in the north of TC Hagibis during the warm run. Further investigation showed that the approach to the westerly jet presumably induced the low local inertial stability as well as the southwesterly vertical wind shear enhancing the upward mass flux in the north of the TC. They led the enhanced upper-tropospheric northward outflow from the TC energized by the warm SST, and it resulted in the decrease of the Z500 in the north. This study suggests that warm SST can affect TC tracks through interaction with mid-latitude westerly jets.