Why are areas controlled by westerly winds mild and rainy?

To put it simply: the westerly wind blows from the sea to the land, so there is more precipitation on the west coast of the continent in the westerly belt (note: it is the west coast of the continent!).

The high-pressure zone is formed by the sinking airflow. As the airflow sinks, the altitude gradually decreases and the temperature gradually increases. Therefore, water vapor is not easy to condense, resulting in dry weather. And because the subtropical high is above It is near 30 degrees north and south latitude, so the temperature is high all year round, resulting in hot and dry weather. For example: Sahara region.