July is set to become Shanghai's hottest month since records began.

Just two more days with temperatures over 35 degrees Celsius and the number of high temperature days will have beaten the 23 recorded in July 1934.

A boy cools himself in a fountain in Hangzhou yesterday. [Photo/Shanghai Daily]

"The average temperatures from July 1 to 27 are higher than that in the same days in the weather history of Xujiahui observatory," said Zhang Ruiyi, a chief service officer at the Shanghai Meteorological Bureau. "It's rare to see six hot days with highs above 38 degrees in July."

The Xujiahui weather station was built to monitor temperatures in 1873. Shanghai has already beaten the record for its hottest day - that was on Friday when the official temperature was 40.6 degrees.

Yesterday, temperatures soared to 38.1 degrees and today they will vary from 30 to 39 degrees.

The next two days will see the high drop slightly to around 37 degrees due to the weakened subtropical high. By Thursday, temperatures will be above 39 degrees again.

Along with the heat wave, afternoon thundershowers are possible this week.

The hot weather is set to continue into August with temperatures possibly reaching 40 degrees. But there may be some relief after August 7, which is liqiu or autumn begins in the Chinese calendar.

Meanwhile, residents in the Zhoupu area in Pudong saw some hail over the weekend. Weather experts said hail was normal during storms.

Air quality was acceptable yesterday with an air quality index of 91, the second lowest level of a six-scale system.