kyou wa kaze ga yowai desu.

The wind is weak today.

Breakdown of kyou wa kaze ga yowai desu.

• は: topic particle
• です: to be
• 今きょ日う: today
• が: subject particle

Questions & Answers about kyou wa kaze ga yowai desu.

How is this sentence put together grammatically?

A natural breakdown is:

• 今日 = today
• は = topic marker
• 風 = wind
• が = subject marker
• 弱い = weak
• です = polite ending

So the structure is roughly:

As for today, the wind is weak.

Japanese often puts the topic first, then says something about it.

Why does 今日 use は?

は marks the topic of the sentence: what the sentence is about.

So 今日は means something like:

• as for today
• today, ...

It sets the time frame for the statement. In English, we often just put today at the beginning without any marker, but Japanese usually uses a particle to show the role of the word.

Why does 風 use が instead of は?

In this sentence, 風が弱いです means the wind is weak.

Here, が marks 風 as the thing that has the property weak. With adjectives like 弱い, が is very common for the thing being described.

So:

• 今日は = as for today
• 風が = the wind
• 弱いです = is weak

If you said 風は, the nuance would shift a little more toward as for the wind... or contrast, depending on context. But 風が弱いです is a very normal way to say it.