kaze ga tuyoi hi ha, sakura ga sugu titte simaimasu.

They mark two different subjects in two different parts of the sentence.

• 風が強い日 = a day when the wind is strong
  • Here, 風が is the subject of 強い
• 桜がすぐ散ってしまいます = the cherry blossoms quickly fall/scatter away
  • Here, 桜が is the subject of 散ってしまいます

So the sentence is built like this:

• [風が強い日] は、[桜がすぐ散ってしまいます]。

A natural way to think of it is:

• As for days when the wind is strong, the cherry blossoms quickly fall.

Yes. In Japanese, a whole clause can come before a noun to modify it.

• 風が強い日
• literally: wind is strong day
• natural English: a day when the wind is strong / windy day

This is a very common pattern in Japanese:

• 雨が降る日 = a day when it rains
• 人が多い店 = a store with lots of people / a busy store
• 私が好きな本 = a book that I like

So 強い is not standing alone here; 風が強い is modifying 日.

Here, 日 is being treated as the topic/condition, not just a simple time marker.

• 風が強い日は = on days when the wind is strong / as for windy days

Using は gives a sense like:

• when it is a windy day, ...
• as for windy days, ...

You could think of it as setting the scene or condition for what follows.

Why not に?

• に often marks a specific point in time.
• Here, the meaning is more general: whenever it is a windy day.

Why not で?

• で usually marks a place, means, or cause/context in a different way.
• It is not the natural particle here.

散る literally means to scatter or to fall apart/scatter away.

With 桜 or 桜の花, it refers to cherry blossoms falling from the tree, often one after another, like petals being blown away.

So in this sentence:

• 桜が散る = the cherry blossoms fall
• more vividly: the blossoms scatter/fall off

It is a very common verb for flowers, especially cherry blossoms.

〜てしまう often adds one of these nuances:

1. completion: something ends up fully happening
2. regret/unfortunate feeling: something happens and it is a bit unfortunate
3. sometimes just emphasis that the action is done completely

Here, 散ってしまいます suggests more than just fall.

• 散ります = fall/scatter
• 散ってしまいます = end up falling / fall away completely / unfortunately fall quickly

With cherry blossoms, this often carries a slight feeling of “they’re gone already” or “they don’t last.”

Because these are different grammar patterns.

• 散ってしまいます = end up scattering/falling away
• 散っています = are scattered / are in the state of having fallen

So:

• 桜が散ってしまいます focuses on the event happening
• 桜が散っています focuses on the resulting state

In this sentence, the point is that on windy days, the blossoms quickly fall off, so 〜てしまう fits much better.

すぐ means quickly, soon, or right away, depending on context.

Here it means the blossoms do not last long once the day is windy:

• 桜がすぐ散ってしまいます
• the cherry blossoms quickly fall
• the blossoms soon scatter away

It modifies the verb phrase 散ってしまいます.

In Japanese, the non-past form often expresses:

• present
• future
• habitual action
• general truths

So 散ってしまいます here does not mean only will fall in one specific future event. It can mean:

• they fall
• they tend to fall
• they will quickly fall

In this sentence, it expresses a general tendency:

• On windy days, cherry blossoms quickly fall.

The ます form simply makes it polite.

They are very close, and both are natural.

• 風が強い日 = a day when the wind is strong
• 風の強い日 = a day of strong wind / a windy day

The first feels more like a full clause modifying 日. The second is a more compact noun-linking style.

In many contexts, they are almost interchangeable.

In literal dictionary terms, 桜 is cherry tree/cherry blossom depending on context.

But with the verb 散る, people naturally understand it as the blossoms that are falling, not the tree itself.

So in this sentence:

• 桜が散る is understood as
• the cherry blossoms fall/scatter

This kind of context-based interpretation is very common in Japanese.

It is:

• [Condition/Topic] は、 [main statement]。

More specifically:

• 風が強い日 = days when the wind is strong
• は = topic marker
• 桜が = subject
• すぐ = quickly
• 散ってしまいます = end up falling/scattering away

So the structure is:

• As for days when the wind is strong, cherry blossoms quickly fall away.

Or more naturally in English:

• On windy days, the cherry blossoms quickly fall.

Japanese usually does not need a dummy subject like it.

In English, we say:

• It is windy
• The wind is strong

In Japanese, the second pattern is common:

• 風が強い = the wind is strong

So instead of saying something like it is a strong-wind day, Japanese directly says:

• wind is strong day

This is one reason Japanese sentence structure can feel very different from English at first.