It really is a simple concept with some complexities that can make for humidity or lack of humidity. The area of high pressure over our area encompasses a massive part of the continent.
First, by definition high pressure has divergent winds, or winds moving away from its circulation. These types of winds moving away from the pressure area tend to discourage the making of clouds. Clouds need an upward movement of air molecules to build which is generally created with lower pressure.
Another aspect to consider with higher pressure is where it originated and where it’s coming from. In today’s instance, we see the high-pressure area moving in from the north, creating north to northeast winds which tend to reinforce dry humidity values.
Many times during August we see a southern area of high pressure which originates from Bermuda. This generally encourages a flow of air from the south and Gulf of Mexico which can create those oppressive humidity values which we many times associate with August days.