A high of 34.9 degrees Celsius was recorded at the main Xujiahui weather station on Sunday, making it the hottest day this year.
And the mercury is headed for 37 this week for at least five days from Wednesday.
On Sunday, Minhang, Qingpu, Songjiang and Jinshan districts released a yellow heatwave alert when the temperature reached above 35 degrees Celsius.
After saying goodbye to the plum rain season over the weekend, this week a subtropical high-pressure system will take control of the city and bring plenty of sunshine as well as warmth.
Humidity will largely remain unchanged in the mid-70s.
Expect showers or thundershowers to pop up in some parts in the afternoon or at night.
The mercury will range between 28 and 36 degrees on Monday and Tuesday.
From Wednesday, it will hit 37 degrees and remain at that level through the weekend.
The weather bureau says that due to the much longer plum rain season, this year’s first high-temperature day — day with a high of 35 degrees or above — came later than usual.
The city’s weather history shows that Shanghai often received its first high-temperature day on June 18 on average.
But there have been exceptions. In 2015, the first high-temperature day was recorded on July 26.
The bureau also warns air quality may get a bit poorer.