Why is Shenzhen a subtropical monsoon climate instead of a tropical monsoon climate?

The most striking feature of tropical climate is that the temperature is high all the year round, and the boundaries between the four seasons are not obvious.

Although Shenzhen is located at 22.5 degrees north latitude, due to the influence of monsoon, southeast winds prevail in summer, with high temperature and rainy weather. The northeast monsoon prevails in other seasons, with dry weather and mild climate. Affected by cold air mass in winter, the temperature difference between winter and summer is large. Climate characteristics are more similar to subtropical climate. So Shenzhen belongs to subtropical monsoon climate.