How should I interpret the function of these words in this phrase 今日は雨だ。?

Question

Suppose you want to make a literal translation of the phrase (and not adapt it to the language to sound natural)

今日は雨だ

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)

Answer 1

The key idea is that your sentence has its subject omitted. So it is inferred by a listener. Actually 「今日」 is not the subject but the topic specified by 「は」 here.

In the case of 「今日は雨だ」, 「雨」 (ame) is close in meaning to "the rainy weather." Thus the subject is inferred to be "the weather (today)." So the most (and excessively) literal translation would be "The weather is the rainy one today."

This kind of implicit subjects is not due to "da" nor "ame," but due to the omission of the subject. For example, the same applies to the following sentence which does not use "da" nor "ame."

今日は[寒]{さむ}い。 / kyō wa samui.
(It's) cold today.

Answer 2

While the delivery time is just ten o'clock, but your watch tells you past of ten o'clock, you must say

もう駄目{だめ}だ。I give up!

"もう駄目" has the same meaning but "もう駄目だ" is more definitive.

"今日は雨" tells just the fact, but "今日は雨だ" has more meaning than it. We can understand the implication from the context.

You and youf family were planning on going to Disney Resort, but you found it was rain in the morning, you might say "今日は雨だ"

After a number of days without rain in the summer, it finally begins rain, and you might say "雨だ！"

I don't know this kind of English word.

In some cases "finally" can be the English word of "だ."