Meaning of なると
What is the meaning of the phrase "なると" in this sentence:
なる is the verb "to become". When used as part of a larger sentence, Xになると means something like "when it comes to X, ..." or "When it becomes X, ..."
So for example:
秋になると葉は黄色くなる "When it becomes autumn, the leaves turn yellow." or simply "In autumn, the leaves turn yellow."
It can also mark less time-specific "moments". For example:
"When water freezes and becomes solid, we call it ice."
It also doesn't need to be about time at all. For example:
"When it comes to jazz, he loses himself (in the music)."
In your example, it means "Every year, when it becomes August"
Like the others said it means something like "when it becomes". なる is the verb "to become" and と can be seen as "when", in the sense that the first part of the sentence is a precondition for the second part. It should be noted that using と like this is usually done when stating something that happens regularly, or general knowledge.
Simple example: 冬になると、寒くなります。"When it becomes winter, it gets cold."