Depois da chuva, os ônibus voltaram a sair da estação.

Because da is the normal contraction of de + a in Portuguese.

• de = of / from / after (depending on context)
• a = the (feminine singular article)

So:

• de + a chuva → da chuva

This kind of contraction is very common and usually required in normal Portuguese.

Other examples:

• de + o → do
• de + os → dos
• de + as → das

So depois da chuva is the natural form.

The phrase Depois da chuva is an introductory time expression: it sets the scene before the main clause.

So the sentence is structured like this:

• Depois da chuva, = after the rain
• os ônibus voltaram a sair da estação. = the buses resumed leaving the station

In Portuguese, as in English, a comma is often used after a longer introductory phrase. It is especially common in writing. You may sometimes see sentences without that comma in informal contexts, but here the comma is perfectly standard and natural.

Portuguese uses definite articles much more often than English.

In English, you might say simply buses. In Portuguese, it is very common to say os ônibus when referring to a specific group or to buses in a general real-world situation already understood from context.

So os ônibus can sound more natural than leaving the article out.

This is one of the big differences from English:

• English: Buses resumed service
• Portuguese: Os ônibus voltaram a sair

Because of the article os and the verb voltaram.

• os = masculine plural the
• voltaram = they returned / resumed

So even though ônibus has the same form in singular and plural, the other words show that it is plural here.

Compare:

• o ônibus voltou = the bus resumed / returned
• os ônibus voltaram = the buses resumed / returned

Ônibus is one of those nouns that does not change form between singular and plural.

So:

• o ônibus = the bus
• os ônibus = the buses

Portuguese has a small number of nouns like this. The article and verb usually make the number clear.

The circumflex accent in ônibus shows the stressed vowel and helps indicate pronunciation.

ônibus is pronounced with stress on the first syllable:

• Ô-ni-bus

In Brazilian Portuguese, it sounds approximately like:

• OH-nee-boos

The accent also helps distinguish the correct stress pattern, since without it a reader might guess the stress incorrectly.

This is a very common Portuguese structure:

• voltar a + infinitive

It means:

• to do something again
• to resume doing something
• to start doing something again after a pause/interruption

So:

• voltaram a sair = they started leaving again / they resumed leaving

In this sentence, the idea is that the rain had interrupted service, and afterward the buses resumed departing from the station.

Because the pattern is:

• voltar a + infinitive

Here:

• voltaram = they resumed / returned
• a sair = to leave / to go out

So the full idea is:

• voltaram a sair = resumed leaving

This a is not the feminine article a. It is a preposition that belongs to the verbal expression voltar a.

Other examples:

• Ela voltou a trabalhar. = She went back to work / resumed working.
• Começamos a estudar. = We started studying.

Yes, but the nuance is a little different.

• voltaram a sair emphasizes resuming after an interruption
• saíram de novo emphasizes doing it again

In this sentence, because the rain likely stopped the departures, voltaram a sair is the more natural choice. It suggests that service had been interrupted and then restarted.

So:

• Os ônibus saíram de novo da estação is understandable
• Os ônibus voltaram a sair da estação sounds more idiomatic for a service resuming

Voltaram is the pretérito perfeito (simple past / preterite) of voltar, in the third person plural.

Conjugation:

• eu voltei
• você/ele/ela voltou
• nós voltamos
• vocês/eles/elas voltaram

Here it matches os ônibus, which is third person plural.

In this sentence, the preterite presents the resumption as a completed event in the past:

• after the rain, the buses resumed leaving

Because the subject is os ônibus, which is plural.

Portuguese verbs must agree with the subject in number and person.

So:

• o ônibus voltou = singular
• os ônibus voltaram = plural

This agreement is very important in Portuguese.

Because the verb sair normally takes de to express where something leaves from:

• sair de algum lugar = to leave from somewhere

And since estação is feminine singular and has the article a, you get:

• de + a estação → da estação

So:

• sair da estação = to leave the station / depart from the station

Because Portuguese often uses an article when referring to a specific place that is understood in context.

• da estação suggests from the station (a particular station)
• de estação would sound incomplete or unusual here

So if we are talking about a known station, da estação is the natural choice.

No. Estação can mean different kinds of station depending on context.

It can refer to:

• a train station
• a bus station
• a subway/metro station
• another type of station

In this sentence, because the subject is os ônibus, the most likely interpretation is a bus station or terminal. But the word itself is broader than just train station.

Yes. Portuguese word order is somewhat flexible.

For example, you could also say:

• Os ônibus voltaram a sair da estação depois da chuva.

This is also correct. The difference is mainly emphasis:

• Depois da chuva, ... puts the time condition first
• Os ônibus ... depois da chuva keeps the subject first and adds the time phrase later

Both are natural.

A careful pronunciation would be approximately:

de-POIS da SHOO-va, uz Ô-ni-bus vohl-TA-rãw a sa-IR da es-ta-SÃW

A more IPA-like version is roughly:

[dʒeˈpɔjs dɐ ˈʃuvɐ, uz ˈõnibʊs vowˈtaɾɐ̃w a saˈiɾ dɐ istaˈsɐ̃w]

A few useful pronunciation notes:

• depois: stress on the second syllable
• chuva: ch sounds like English sh
• os ônibus: in connected speech, os often sounds like uz
• voltaram: the final -am is nasal in Brazilian Portuguese
• estação: final -ão is nasal too

Not always. Depois de can be followed by many things.

Examples:

• depois da chuva = after the rain
• depois do almoço = after lunch
• depois de estudar = after studying
• depois de ela chegar = after she arrives/arrived

A contraction happens only when de is followed by an article:

• de + a = da
• de + o = do

So depois da chuva contracts because chuva is preceded by a.

Literally, sair often means to go out or to leave, but in this context depart or leave is better.

With buses, trains, planes, etc., sair often means:

• to leave
• to depart

So os ônibus voltaram a sair da estação is best understood as:

• the buses resumed leaving the station
• the buses started departing from the station again

Using go out in English would sound unnatural here.

Yes, it is natural and correct.

It sounds like standard written Brazilian Portuguese and would be understood easily. Depending on context, native speakers might also say things like:

• Depois da chuva, os ônibus voltaram a circular.
• Depois da chuva, os ônibus voltaram a sair do terminal.
• Depois da chuva, os ônibus retomaram as saídas da estação.

But the original sentence is perfectly normal.