"Ramadan is coming" means the same as "Ramadan is approaching". You can always say it. There are no rules other than the rule that says that what you say should always agree with what you are think. If, in your mind, you think of it as approaching, then that is what you should say.

You could say Ramadan is in March, my birthday is in September. Or, my friends are coming for dinner tonight/next week on Saturday.

You can definitely use "is coming" for events that are a few months away, as long as the event is approaching in the near future and it's something that people are generally aware of or anticipating. It's not limited to events that are just around the corner. For example: * "Ramadan is coming" works fine, even though it's a couple of months away. It implies that it's approaching soon and that people are preparing for it. * "The event is coming in September" can also be used, though it may sound a bit less immediate than "Ramadan is coming." You could also say "The event is coming up in September" to make it sound a bit more natural if you want to refer to it in a more specific way. So, it's about the context and the level of anticipation—"is coming" generally conveys something expected to happen soon enough that people are starting to think about or prepare for it, even if it's a few months away.