Why are those weather conditions with humid air called Hui Nan Tian?

In the south, the very humid south wind days are called "Hui Nan Tian". The air is very humid, and water will appear on the floor. In spring, water will appear on the walls and floors of Hui Nan Tian. In fact, the principle of sea fog is very similar. Warm and moist ocean air flows from the warmer sea surface to the cooler sea surface. The water vapor in the air condenses into fog droplets when cooled, and accumulates in the air to form fog. If the sea surface temperature difference through which the air flow passes is large, the chance of fog forming will also be greater. Likewise, walls and floors become cold both on the outside and inside due to the cold winter weather. If warm and humid air flows through the walls and floors at this time, the moisture in the air condenses into water droplets when cold, and adheres to the walls and floors. It seems that water is seeping from the walls and floors. In summer, even if there is moist ocean airflow, the surface and inside of the walls and floors are not cold enough, and water will not come out of the walls and floors.