China has endured its second-hottest sanfu period on record this year, and forecasters warn that high temperatures will persist in the south even though the period has ended.

Average national temperatures reached 23.21 C during the period, which ran from July 20 to Aug 18. It was the second highest sanfu on record, according to Weather China, a website affiliated with the China Meteorological Administration. The figure narrowly trailed the 23.24 C average recorded in 2024.

Sanfu is the hottest and most humid stretch of the year, according to the Chinese lunar calendar.

Despite lasting only 30 days, this year's sanfu heat was exceptionally intense, Weather China said.

The heat wave set new average-temperature records in Shaanxi province and the Xizang autonomous region, while the Sichuan, Henan and Shanxi provinces logged their second-hottest sanfu on record.

Persistence was also notable, with more than 100 national meteorological stations reporting record numbers of high-temperature days. Yicheng in Hubei province, Ganluo in Sichuan and Luohe in Henan each broke previous records, experiencing more than 20 days of extreme heat; previously, none of the regions had seen more than nine days of such temperatures.

Tang Xiaojing, a weather analyst with Weather China, attributed the extreme heat to a particularly strong and northward-positioned subtropical high.

"This system extended its influence across central North China and the Sichuan Basin, causing widespread and intense heat due to descending warm air currents," she said.

Although sanfu has ended, scorching weather persists across regions south of the Yellow and Huaihe rivers as the subtropical high remains strong, Weather China said.

Daytime highs could reach up to 40 C in cities such as Hangzhou in Zhejiang province, Nanjing in Jiangsu province and Shanghai. Nighttime lows are expected to hover near 30 C in some areas.

On Wednesday morning, the National Meteorological Center issued a yellow alert for high temperatures, the lowest in its three-tier warning system. Forecasts said most areas along the Yellow and Huaihe rivers, the Yangtze River region, southern Shaanxi and the Sichuan Basin would see highs of 35 C to 39 C.

In some places, including Shandong, Henan and Zhejiang provinces, temperatures could climb above 40 C.