"J'ai une annonce surprenante à faire."
Translation:I have a surprising announcement to make.
For adjectives that change meaning depending on placement, read this link:
It will give you an idea why adjectives are placed before or after the noun.
But surprenant does not appear in the cited link. Are you saying that it varies in meaning according to its position? I am not sure that I can see figurative and literal meanings of "surprenant" to help me decide the position except maybe something that actually gives me a physical reaction is more literally surprising, but that would not seem to be the case here where the positioning of the adjective after the noun suggests a literal surprise of the physical kind, whereas an announcement is more likely to deliver a subjective kind of surprise and so require a position before the noun.
I have seen it used both before and after the noun. I have also seen an article saying that adjectives based on participles always come after the noun.
I have had "nouvelles surprenantes" marked as wrong and "surprenantes nouvelles" given as the correct answer, but here "une annonce surprenante" is the correct form. Reverso context shows both positions, before and after, are widely used without any discernible pattern.
Can you add anything to help decide where this pesky adjective should go in any given situation?
"Surprenante" is one of these regular adjectives which can have a more subjective meaning when placed before the noun they modify.
If I mention "une surprenante nouvelle", it means that it was a surprise to me, not necessarily for the rest of the world.
If I mention "une nouvelle surprenante", it means that probably most people would find it surprising.