"O ploaie grea vine in cateva minute" is really in the wrong order?
Nope, that's a good translation.
Heavy rain is „Ploaie torențială” - what a hell is „ploaie grea”?! It doesn't exist such a thing in Romanian! Hey! I'm Romanian! Believe me!
Hey! We are just learning limbă română... We don't know alllll the words yet... (And we'll not learn them in one lesson...)