Güvenlik anonsu yapılmak üzereyken dalga yüksekliği arttı.

No. In güvenlik anonsu, the -u is not the accusative ending.

This is a very common Turkish noun compound pattern:

• güvenlik = safety, security
• anons = announcement
• güvenlik anonsu = safety announcement

This is called an indefinite noun compound. The second noun usually takes a 3rd person possessive suffix:

• kahve fincanı = coffee cup
• yaz tatili = summer vacation
• güvenlik anonsu = safety announcement

So here, anonsu means its announcement / announcement of safety in structure, though in natural English we just say safety announcement.

If it were accusative, the function and context would be different.

Yapılmak üzereyken means something like:

• when it was just about to be done
• right as it was about to be made
• while it was on the point of being made

It breaks down like this:

• yapılmak = to be done / to be made
  
  • from yapmak = to do, make
  • yapılmak is the passive infinitive
• üzere = about to, for the purpose of, on the verge of
• -yken = when / while

So:

• yapılmak üzere = about to be made
• yapılmak üzereyken = when it was about to be made

This structure often gives the feeling of something happening at the last moment, just before another action.

Because the announcement is being made, not making something.

Compare:

• anons yapmak = to make an announcement
• anons yapılmak = for an announcement to be made

In the sentence, the announcement is the thing receiving the action, so Turkish uses the passive:

• Güvenlik anonsu yapılmak üzereyken...
• literally: When the safety announcement was about to be made...

If you used yapmak, it would sound like the announcement itself was doing the action, which does not fit.

-yken means when or while.

It connects a background situation to the main event.

In this sentence:

• Güvenlik anonsu yapılmak üzereyken = when the safety announcement was about to be made
• dalga yüksekliği arttı = the wave height increased

So -yken sets the time frame for the main action.

A few similar examples:

• Ben evdeyken aradı. = He called when I was at home.
• Tam çıkacakken yağmur başladı. = Just as I was about to leave, it started raining.

Here, üzereyken gives a stronger sense of just before than plain -yken would.

Because the sentence is specifically talking about the height of the waves, not simply the waves.

Breakdown:

• dalga = wave
• yükseklik = height
• dalga yüksekliği = wave height

This is another noun compound, just like güvenlik anonsu.

So the subject of the main clause is:

• dalga yüksekliği = the wave height

And:

• arttı = increased / rose

So the full main clause means:

• the wave height increased

If the sentence said just dalga arttı, that would not express the same idea.

Because artmak and artırmak are different verbs.

• artmak = to increase, rise, go up
  
  • usually intransitive
• artırmak = to increase something, raise something
  
  • usually transitive

In this sentence, the wave height itself changes:

• dalga yüksekliği arttı = the wave height increased

No outside agent is increasing it.

Compare:

• Fiyatlar arttı. = Prices increased.
• Hükümet vergileri artırdı. = The government increased taxes.

So arttı is correct because the subject undergoes the change by itself.

Not really. It is very natural Turkish word order.

The sentence is structured like this:

• [Time/background clause] + [main clause]
• Güvenlik anonsu yapılmak üzereyken
  • dalga yüksekliği arttı

This is very normal in Turkish. Turkish often puts:

• time expressions,
• background information,
• subordinate clauses

before the main clause.

A more literal English-style order would be possible in Turkish too, for example:

• Dalga yüksekliği, güvenlik anonsu yapılmak üzereyken arttı.

But the original version sounds smooth and natural.

Not with the same meaning.

These are different:

• yapılırken = while it was being done / made
• yapılmak üzereyken = when it was about to be done / made

So:

• Güvenlik anonsu yapılırken dalga yüksekliği arttı. = The wave height increased while the safety announcement was being made.

But the original sentence means:

• The wave height increased just as the safety announcement was about to be made.

So yapılmak üzereyken expresses imminence, not an action already in progress.

It can mean either safety or security depending on context, because güvenlik covers both areas in Turkish.

In güvenlik anonsu, the most natural English translation is often:

• safety announcement

especially in contexts like:

• transport
• ships
• airplanes
• public warnings

But in another context, it could also be something closer to security announcement.

So the exact English choice depends on the situation, even though the Turkish word stays the same.

Arttı is in the simple past tense.

Breakdown:

• art- = verb stem
• -tı = past tense suffix
  (here it appears as -ttı because of sound changes and spelling)

So:

• arttı = increased / rose

It refers to a completed event in the past.

In the sentence, the background clause does not carry a separate finite tense in the same way English does. Instead, Turkish uses the structure yapılmak üzereyken to express the timing relationship, and the main verb arttı anchors the whole sentence in the past.