Heavy downpours marked the official start of the plum rain season yesterday, and the torrents are set to continue until Thursday, forecasters said.
As much as 120 millimeters of rain are expected to hit some parts of the city today, while almost all areas will see at least 70mm, the city's flood control authority said.
District and county governments have been told to take whatever measures are necessary to prevent the overflowing of waterways.
The city's drainage system will be paralyzed if the Huangpu overflows and inundates the city, the flood authority said.
Qingpu was the city's wettest district yesterday, recording 41mm at 6:30pm, against a benchmark of 36mm at the Xujiahui weather station.
The heavy downpours added to the usual congestion during the evening rush hour. Traffic police said serious jams were reported on nine of the city's elevated highways.
The mercury is forecast to fall to 24 degrees Celsius today and tomorrow, before rising as the first round of plum rains fizzles out on Thursday evening.
The high temperature will be between 25 and 26 degrees on Thursday and Friday, before rising to 28 degrees on Saturday.
