[greggy83]

I don't completely agree with Susan53.

I think the use of 'I hope [that] it will happen' is a casual and ungrammatical structure; the more appropriate and fail-proof sentence would be 'I hope [that] it happens'. This verb form for 'happens' is a subjunctive from what I understand. I surmise that the key for figuring out whether the subjunctive is used is to see whether 'that' could be written in.

Also, using 'hope' is not a prediction: it's merely a wish or a yearning.