Heatwaves are forecast to return to China over the next 10 days after a brief respite, with high temperatures expected from east to west, meteorologists warned. A sharp spike in temperatures is expected as soon as Saturday, known as the day of the “big heat” on the Chinese Almanac, before building up into heatwaves, defined as periods of atypically hot weather of three days or more. The hot spell is expected to be similar in scope as heatwaves from July 5-17, but more regions could be hit by temperatures of 40 degrees Celsius (104F) or higher, Fu Jiaolan, chief forecaster at the center, told state media on Thursday. A yellow alert, the lowest in a three-tier warning system, was raised on Friday for the manufacturing provinces of Zhejiang, Fujian and Guangdong, indicating temperatures of 35C can be expected over the next three days. The three coastal provinces, as well as parts of Hunan, Jiangxi and Chongqing, stand at risk of forest fires in the near term, while the load on the national power grid is expected to reach a new high, with safe operation expected to face “severe tests,” the Ministry of Emergency Management warned on Friday. The heat this summer has been described by Chinese weather watchers as extreme, boosting demand for air-conditioning by homes, offices and factories and pushing the load on power grids in more than a dozen provinces to records. From June 1 to July 20, parts of the Yellow River and Yangtze River basins — major centers of industry and commerce — were hit by at least 10 high-temperature days more than the norm. Since June, heatwaves have also pounded other parts of East Asia, Western Europe, North Africa and North America, sparking wildfires in many countries. Scientists caution that climate change will only make heatwaves hotter and more frequent. The highest-ever recorded temperature in China is a matter of debate. According to Chinese media, the hottest period in the last 300 years was in July 1743 during the Qing dynasty, with a French missionary in Beijing said to have recorded an all-time high of 44.4C. In 2015, a news portal in Xinjiang reported 50.3C at a weather station near Ayding, a dry lake in the Turpan Depression, one of the hottest places in China during summer.