kyou ha kaze ga yowai desu.

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.

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.

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.

Because 弱い is an i-adjective, and in Japanese, i-adjectives can act as predicates by themselves.

So:

• 風が弱い = the wind is weak

There is no separate word exactly like English is needed there.

This is a very important difference from English. Japanese adjectives can often finish the sentence on their own.

弱い is an i-adjective.

You can tell because it ends in い in its dictionary form.

That matters because i-adjectives behave differently from na-adjectives. For example:

• 弱い → i-adjective
• 静か → na-adjective

With an i-adjective, you do not put な before a noun, and you do not need だ before です in a sentence like this.

So:

• 風が弱いです = correct
• 風が弱いだです = incorrect

です makes the sentence polite.

Compare:

• 今日は風が弱い。 = plain
• 今日は風が弱いです。 = polite

With an i-adjective, you can add です at the end to make the sentence sound more polite, even though 弱い is already the predicate.

So です here is not exactly the same as English is. It is mainly a politeness marker in this kind of sentence.

Yes. Japanese commonly describes wind as:

• 風が強い = the wind is strong
• 風が弱い = the wind is weak

This is very natural Japanese.

In English, learners may expect something like light wind or the wind isn’t strong, but Japanese often uses the direct pair strong / weak for wind.

The standard readings are:

• 今日 → きょう
• は → pronounced わ here, because it is the topic particle
• 風 → かぜ
• が → が
• 弱い → よわい
• です → です

So the whole sentence is read:

きょう は かぜ が よわい です。

Yes, you can.

• 今日は風が弱いです。
• 今日の風は弱いです。

Both are grammatical, but the nuance is a little different.

今日は風が弱いです

• means As for today, the wind is weak
• focuses first on today

今日の風は弱いです

• means Today’s wind is weak
• treats today’s wind as a noun phrase

The original sentence is usually the more natural everyday way to describe today’s weather.

It is possible in some contexts, but it has a different nuance.

風は often suggests contrast, like:

• As for the wind, it’s weak
  (maybe implying something else is not weak)

For a simple neutral statement about the weather, 風が弱いです is more natural.

So if you are just saying The wind is weak today, the original sentence is the better choice.

Yes, if the time is already understood from context.

For example:

• 風が弱いです。 = The wind is weak.

Japanese often leaves out information that is obvious from the situation. But if you want to clearly say today, keeping 今日は is natural.

The spaces are usually only for learners.

Normal Japanese writing would be:

今日は風が弱いです。

Japanese normally does not put spaces between words the way English does. Learning materials often add spaces so you can see the parts more easily.