Вересень холодний.

In Ukrainian, the verb to be is usually left out in the present tense.

So:

• Вересень холодний. = September is cold.

Literally, it looks like September cold, but that is normal Ukrainian grammar.

If you add є here, it usually sounds unnecessary or unnatural in a basic sentence like this.

Because холодний has to agree with вересень.

Вересень is:

• masculine
• singular
• nominative

So the adjective also has to be:

• masculine
• singular
• nominative

That gives холодний.

Compare:

• зима холодна — winter is cold
• море холодне — the sea is cold
• дні холодні — the days are cold

Yes. In Ukrainian, a noun ending in ь is not automatically feminine.

Вересень is a masculine noun. In fact, the names of the months like січень, березень, вересень, жовтень are masculine.

So even though the ending may look unusual to an English speaker, the adjective must still use the masculine form: холодний.

Because this sentence is using холодний as a predicate adjective: it tells you what Вересень is like.

So:

• Вересень холодний. = September is cold.

If you put the adjective before the noun:

• холодний вересень

that usually means a cold September or cold September as a noun phrase, not a full neutral statement.

So the word order helps show the difference between:

• a sentence: Вересень холодний
• a noun phrase: холодний вересень

Yes, and that is actually a very common and natural way to express the idea.

The difference is:

• Вересень холодний. — September is cold.
  This describes September itself.

• У вересні холодно. — It is cold in September.
  This describes the weather/conditions in September.

So both are correct, but they focus a little differently. Ukrainian often likes the холодно pattern for talking about general weather.

Normally, month names are not capitalized in Ukrainian.

So in the middle of a sentence, you would usually write:

• вересень

Here it is capitalized only because it is the first word of the sentence:

• Вересень холодний.

This is different from English, where month names are always capitalized.

The ь is the soft sign. It does not make its own sound. Instead, it makes the preceding consonant softer.

So in вересень, the final н is pronounced softly.

This is a very common feature of Ukrainian spelling and pronunciation. When you see ь, think:

• no separate vowel
• the previous consonant becomes soft

Because вересень is the subject of the sentence, so it is in the nominative case.

• Вересень холодний. — September is cold.
  Here September is the subject.

But after the preposition у meaning in, you need a different case form:

• у вересні — in September

So:

• вересень = nominative
• у вересні = locative

Yes, Ukrainian word order is fairly flexible, but the meaning or emphasis can shift.

• Вересень холодний. — the most straightforward statement
• Холодний вересень. — usually sounds like a cold September or gives stylistic emphasis

So while Ukrainian allows movement of words more freely than English, not every order feels equally neutral.

For a simple beginner sentence meaning September is cold, Вересень холодний is the best choice.

Yes, it is grammatical and natural.

That said, in everyday speech, Ukrainians might often prefer a weather-style expression such as:

• У вересні холодно.

But Вересень холодний is still perfectly good Ukrainian, especially if you are describing the month as a whole or contrasting it with other months.