Typhoon Bailu will land in Fujian. Why does typhoon transit bring heavy rain?

This is actually related to the structure of typhoon and the mechanism of typhoon maintenance. The typhoon can be maintained because the heat energy is converted into kinetic energy, and the heat energy comes from the evaporation of water vapor on the surface of tropical high-temperature ocean. In order to release heat energy, these steam must undergo a phase change, that is, from gas to liquid water, and a large amount of energy is released into kinetic energy, which in turn extracts more high-temperature steam, which releases heat energy, thus forming a heat engine. Therefore, a large amount of liquid water is released from typhoons and falls to form heavy rain.

However, in some cases, a typhoon can also suck in a lot of warm and humid air from another typhoon vortex nearby or the warm and humid air in the southwest airflow area. This supply of "energy nutrition" may make a dying vortex stronger again, which may lead to an abnormal rainstorm when the typhoon lands.

For example, Taiwan Province Province has been hit by torrential rains and floods that are rare in history. These disasters can be attributed to Typhoon Morakot, which was near the island of Taiwan Province Province and connected with typhoon goni in the west. The transmission of water vapor occurred between two typhoon eddies, which led to floods in Taiwan Province Province.

Moreover, the "7.2 1" torrential rain in Beijing at that time was actually related to typhoon activities. At that time, the north side of North China was a mid-latitude westerly trough vortex system, and Beijing was in front of the trough. On the south side, the typhoon vortex along the southeast coast of China and the warm and humid water vapor flow of tropical cyclone in the Bay of Bengal also meet in Beijing area, forming a number of special channels for transporting strong water vapor. The existence and interaction of these "three vortexes" provided dynamic factors, warm and humid water vapor, strong convection and unstable atmospheric structure for the small and medium-scale system formed by local rainstorm, which led to this rainstorm and left unforgettable memories for Beijingers.