What does 1 Samuel 12:17 mean?

It's the wheat harvest now, right? I'm going to call on the Lord, and he's going to send thunder and rain. Then you'll realize how wrong you were to ask for a king. 1 Samuel 12:17 - Modern Text Bible

(Samuel points out that rain during harvest is unusual and destructive, so this miracle will show God's displeasure with their demand for a king.)