Why is the humid weather in Guangdong always in spring?

Every year in Guangdong, there is a "return to Nantian", which lasts for a long time. The "returning to Nantian" in spring is particularly humid because of the continuous low temperature weather during the Spring Festival, and the inside and outside of the building are "cool". After this strong and lasting cold air left, the warm and humid airflow strongly countered, the temperature rose rapidly, and the air humidity increased significantly. Under the influence of warm and humid airflow, there will be serious humidity in the room.