It's muggy and humid today.

I have been in the United States for ten years, and the answer I gave you is the usage of American spoken language, which may not be consistent with the "standard answer" taught in our country, but it is definitely the embodiment of authentic life terms.

1. The weather is sticky (today), or it is sticky (today), or it is sticky (today).

It has been cloudy for several days. (Note that it's here is a conjunction of it has, not It is). Or, another cloudy day.

Today is a sunny day, with no wind and no clouds. Today is a sunny, cloudy and windy day. Or it's sunny (today), with no clouds and no wind in Wan Li.

Today is quoted because it can often be omitted, because the tense itself is the simple present tense, and it is not necessary to say "today".