"But the wind is weak today."
Both particles have nothing to do with subject or topic. The whole construct is called double ga predicate. All four combinations of ga/wa are possible in these two positions. The meaning will be different, of course. Wa establishes that a noun is a part of some broader category and the statement is true at least for the this specific item. For example if you said 風は that would mean that at least wind is weak today, maybe some other weather elements were in contrast strong.
usually that one is used as a conjunction to attach the sentence to another one, similar to continuative form, but sometimes you can omit the sentence that you are attaching. And I think でも sounds more like a statement than using けど
It might rain today....
「 でも、今日は風が弱いです」but, the wind is weak today
do you wanna go fly a kite?
[you responding]「今日風が弱いですけど」but the wind is weak today (similar to how ね works and omitting the sentence that's trying to imply).
I would say that without context both are correct.
you can add it but is not needed, some temporal nouns have a particular property of behaving like adverbs and fall into the category of adverbial nouns as well. When used like this they can be placed at the start to modify the whole sentence by acting directly on the verb.
This is really similar to how you can use normal adverbs at the start of a sentence if there is no topic marker, for example「映画をよく見る」can be change into「よく映画を見る」and both are correct.
Sometimes however you will see a comma in between, I think in those cases is skipping the particle (which is also acceptable on written japanese but only for temporal nouns), and sometimes they use は to bring up the date as a general one, this is similar to how we use plural in english for example: "I'll watch movies on sundays" vs "I'll watch a movie on sunday".
Very confusing sentence. I was under the impression that we usually use は rather than が when attributing an adjective to a subject rather than attributing an action, and that you can usually just omit the は after the time, replacing it with a comma. So I wrote: でも、今日、風は弱いです
Duo said that I missed a word (after 今日) and gave me the corrected sentence: でも今日は風は弱いです
So my question: Can you really have two は particles in the same sentence?? I thought that was forbidden, which is why I tried to omit one.
yes, you can have multiple は in one sentence.
I recommend this video in particular if you want to understand it better:
The video has subs if you have trouble understanding the creepy doll voice, the information in that video is very good though. She also has a series about the differences between using は and が which is amazing.
I was under the impression that we usually use は rather than が when attributing an adjective to a subject
the usual is using が with adjectives, even in duo sentences like ～が好きです、maybe you are confused because In the cases when the speaker is asking a question は is more usual.