The South China region is partially within the tropics. It is the warmest and wettest part of the country during the summer.
Rainfall is very heavy between May and September along the coast and adjacent inlands. Winters are mild and frost free. However, summer heat and humidity can be rather uncomfortable.
Typhoons are frequent here. They can be violent, bringing extreme rains, and strong winds for several days at a time along the coastal regions. The Typhoon season is from July to October.
If you want to combine your China business trip with one or more Trade Fair visits, the weather conditions during the most important Trade Fair periods (April and October) may not affect you much.
I strongly suggest planning your business trip either during the cooler seasons from January to March or from November to December or during the main Trade Fair periods in April and October. Avoid the very hot and humid summer months. Besides the hot humid and unpredictable weather conditions, air pollution dramatically increases. If you have health conditions affected by air pollution it is best to stay away this time of the year.