It’s summertime here in Miami, and the weather is becoming rather predictable: Sunny and hot, then the clouds roll in and it rains, then the clouds clear up and it is sunny again. This is the typical weather in a tropical climate. Many students get frustrated when they look outside in the afternoon and see clouds forming, not realizing that it will clear up in a couple of hours. Often, the afternoon will have rain and then clouds clearing up within the same hour! Once it rains, the humidity clears up tremendously and then the weather is much more comfortable.
Clear up, when talking about weather, means that it becomes sunny! Another week, another idiom for your English course in the US!