1 [only before noun]
a forthcoming event, meeting etc is one that has been planned to happen soon:
Keep an eye on the noticeboards for forthcoming events.
willing to give information about something [≠ unforthcoming]
IBM is usually pretty forthcoming about the markets for its products.
3 [not before noun]
if something is forthcoming, it is given or offered when needed - often used to say that this does not happen:
When no reply was forthcoming, she wrote again.