Abstract:The main characteristics of the atmospheric circulation in the Northern Hemisphere in September 2023 are shown as follows. The polar vortex was unipolar with the same intensity as normal, leaning towards the Eastern Hemisphere. The Eurasian circulation in the middle and high latitudes, to the west of Lake Baikal, was more meridional, and the Western Pacific subtropical high was significantly more westward and stronger than usual. Most of the northern part of China was affected by the horizontal westerly circulation, while most of the southern part was controlled by the subtropical high. In September, the national average temperature was 18.2℃, 1.3℃ higher than that of the same period of normal years (16.9℃), with high temperature mainly appeared in the south to Yangtze River and the South China. The national average precipitation was 69.1 mm, 5.8% higher than the normal value (65.3 mm). Two typhoons were generated in the Northwest Pacific and the South China Sea, which were fewer than those in the same period of the year. In addition, typhoons Saola and Haikui landed in China, successively affecting South China and leading to extremely severe precipitation. The number of landfall typhoons was close to normal. There were six extensive areal severe precipitation processes and two severe convective weather processes in this month. Besides, strong tornadoes hit Suqian and Yancheng of Jiangsu Province.