Suppose you want to make a literal translation of the phrase (and not adapt it to the language to sound natural)
How would you do it? "Today there is rain" or "Today it's rainy"
My question (if possible to answer) it is , is the "da" verb here which works like "there is" or is the "ame" noun here which works like the adjetive "rainy"
Usually I make these questions (which might sound annoying/picky) because I try to have guidelines or rules to understand what is a valid sentence and what's not in japanese, and what could be exceptions. Otherwise everything seems to be a valid sentence. Though I understand that most part of a language is learnt by experience and you can't have a rule for everything (even when software translators try to but they mess big time sometimes or many times)