"Is the wind strong?"
No, as は is the marker for the "topic" of a sentence. が is the marker for the "subject" of a sentence. This is really just one of those things that you have to simply learn to distinguish between with exposure to Japanese, since in English, we don't make this distinction. Generally, は is used for an idea that both speakers already know about. が is used for a new idea, like one from your own head, such as expressing likes/dislikes. There's also a variety of differences between them, but that one seems like the most relevant to this sentence.
So, in this case, かぜ is something already established. We already know what "the wind" is in this sentence. So, therefore, it is correct to use は here rather than が.