Штормовое предупреждение уже объявлено.

Because предупреждение is a neuter singular noun, and the adjective must agree with it.

• штормовый = masculine singular
• штормовая = feminine singular
• штормовое = neuter singular
• штормовые = plural

So:

• штормовое предупреждение = storm warning

Both words are in the same form: nominative singular neuter.

It is in the nominative case.

In this sentence, штормовое предупреждение is the grammatical subject of the passive construction:

• Штормовое предупреждение уже объявлено.

Literally, it is something like:

• The storm warning has already been announced / declared.

Because it is the subject, it stays in the nominative.

Объявлено is a short passive participle in the neuter singular form.

It agrees with предупреждение, which is neuter singular:

• masculine: объявлен
• feminine: объявлена
• neuter: объявлено
• plural: объявлены

So:

• предупреждение объявлено
• warning is/has been announced

This is a very common Russian way to express a passive result or state.

By contrast:

• объявили = they announced
  This is an active verb form, not passive.

So these mean slightly different things:

• Штормовое предупреждение уже объявлено. = The storm warning has already been declared.
• Уже объявили штормовое предупреждение. = They’ve already declared a storm warning.

That is a very common point of confusion.

In Russian, short passive participles like объявлено often describe a resulting state:

• объявлено = declared / announced

So the sentence does not work like a simple English present tense. It expresses that the action has already happened and its result is now true.

That is why English often translates it as:

• has already been declared
• is already declared/announced
  depending on context

Russian does this without a separate word for has been.

Yes, in a sense.

Russian normally omits the verb “to be” in the present tense. So there is no word corresponding to English is here.

• Штормовое предупреждение уже объявлено.

There is no есть in normal usage here.

In the past or future, forms of быть can appear:

• Штормовое предупреждение было объявлено. = The storm warning was declared.
• Штормовое предупреждение будет объявлено. = The storm warning will be declared.

But in the present-result meaning, Russian simply says объявлено.

Уже means already.

It shows that the declaration has happened by now, often a little earlier than expected or earlier than some reference point.

So:

• Штормовое предупреждение уже объявлено.
• The storm warning has already been declared.

Position-wise, уже often goes before the part it modifies, but Russian word order is flexible.

Yes. Russian word order is flexible, although different orders can sound more natural in different contexts.

Standard neutral order:

• Штормовое предупреждение уже объявлено.

Other possible orders:

• Уже объявлено штормовое предупреждение.
• Штормовое предупреждение объявлено уже.
  (possible, but more marked)
• Объявлено уже штормовое предупреждение.
  (context-dependent)

The original sentence is a very natural neutral way to say it.

They express the same event from different angles.

• объявлено = passive, focus on the warning itself
• объявили = active, focus on the people/authority who announced it

Compare:

• Штормовое предупреждение уже объявлено.
  = The storm warning has already been declared.

• Уже объявили штормовое предупреждение.
  = They’ve already declared a storm warning.

Russian often prefers the passive style in official announcements, news, and formal language.

Yes. Предупреждение is the normal word for warning.

It comes from the verb предупредить = to warn / to give advance notice.

In weather and official contexts, предупреждение is very common:

• штормовое предупреждение = storm warning
• предупреждение о шторме = warning about a storm

The fixed expression штормовое предупреждение is the standard phrase you will often see in forecasts and news.

Russian can express this idea in both ways:

• штормовое предупреждение
• предупреждение о шторме

The first is more compact and behaves like a set term: storm warning.

The second is more literal: warning about a storm.

In official weather language, штормовое предупреждение is very common and sounds very natural.

The main stress pattern is:

• штормово́е предупрежде́ние уже́ объявле́но

A rough pronunciation guide:

• штормово́е ≈ shtarma-VO-ye
• предупрежде́ние ≈ pri-du-prezh-DYE-ni-ye
• уже́ ≈ oo-ZHE
• объявле́но ≈ ab-yav-LYE-na

A few helpful pronunciation points:

• ш is like English sh
• ж is like the s in measure
• я after a consonant often gives a ya-type sound
• unstressed о is often pronounced closer to a

It sounds neutral to formal, and very natural in news, forecasts, official notices, or emergency communication.

Because of the passive construction объявлено, it has a slightly official tone, which fits the context well.

A more conversational version might be:

• Уже объявили штормовое предупреждение.

That sounds more like everyday spoken Russian.