Breakdown of Dizem que vai chover amanhã.
amanhã
tomorrow
chover
to rain
dizer
to say
que
that (conjunction)
Questions & Answers about Dizem que vai chover amanhã.
Who is the subject of dizem here?
Just like in English, dizem (they say) is used impersonally here. It doesn't refer to a specific group of people, but rather means "people say" or "it is said."
Can I drop the word que and just say "Dizem vai chover amanhã"?
No. In English, we often drop the word "that" and say "They say it is going to rain." In Portuguese, the conjunction que (that) connecting the two parts of the sentence is absolutely required.
Why use vai chover instead of the actual future tense choverá?
While choverá is grammatically correct, using the verb ir (to go) in the present tense plus an infinitive (like chover) is by far the most common way to express the future in everyday spoken Portuguese.
Why isn't there a word for "it" before vai chover?
Verbs about the weather, like chover (to rain), do not take a subject pronoun in Portuguese. While English requires the dummy subject "it" ("it is going to rain"), Portuguese just uses the third-person verb on its own.