The Shanghai Central Meteorological Observatory issued a blue rainstorm warning signal at 08: 00 on July 29, 2023: Due to the influence of the peripheral circulation of Typhoon Du, the accumulated precipitation in the city reached more than 50 mm on July 29. On the 29th, Shanghai continued to be influenced by the peripheral circulation of Du, with intermittent precipitation as the main factor, short-term heavy rainfall and local heavy rain. Today, the wind is strong during the day. The southeast wind is 6-7, the gust is 5, and the gust along the river is 8, and the temperature is 27℃-30℃ all day.

Experts from the Shanghai Central Meteorological Observatory said that although the typhoon itself is far away from Shanghai, its periphery spiral rain belt is huge, and the periphery will pass through Shanghai, with abundant water vapor, and Shencheng is within the scope of "throwing water". The data shows that there were scattered showers in Shencheng on the 28th, and there was a gust of more than 8 at one time.

Formation conditions of typhoon:

The sea surface water temperature is above 26.5℃; Initial disturbance of a positive vorticity; The shear of ambient wind in the vertical direction is very small; Low pressure or cloud disturbance is at least several latitudes from the equator. Because people don't fully understand the formation of typhoons now, the above list is only a necessary condition for the formation of typhoons. The initial stage of typhoon is tropical depression, and it usually takes about 2 days from the initial low-pressure circulation to the maximum average wind force near the center, only three or four days for the slow one and only a few hours for the fast one.

In the development stage, the typhoon continuously absorbs energy until the central air pressure reaches the lowest value and the wind speed reaches the maximum value. After the typhoon landed, under the joint influence of ground friction and insufficient energy supply, it will quickly weaken the death.