Why are there sultry and humid weather in areas controlled by subtropical high, and some of them are cloudy and sunny?

Let me give you an example first. Typhoon is formed because the air pressure is low, there is little air in the low-pressure area, and the surrounding air is replenished. Due to the Coriolis effect, the supplementary air spirals into the low pressure area and becomes a typhoon. Similarly, the subtropical high is a high-pressure area, where air is scattered around, cold air can't enter, and convective clouds can't enter. Therefore, there will be hot and humid weather in the area controlled by the subtropical high, and some times it will turn sunny to cloudy.

In addition, the air moves from the height to the ground, and the conditions for forming rain are updraft, condensation nuclei, and no updraft, so there is little rain.