A ocorrência foi grave.

A is the definite article meaning the. It agrees with ocorrência, which is a feminine singular noun.

So:

• a ocorrência = the occurrence / the incident
• uma ocorrência = an occurrence / an incident

In this sentence, A ocorrência foi grave refers to a specific occurrence, not just any occurrence.

Yes, ocorrência is feminine.

You can tell this mainly because it takes the article a, not o:

• a ocorrência
• not o ocorrência

The ending -ência is also very often feminine in Portuguese, as in:

• a diferença
• a experiência
• a emergência

So ocorrência follows a common pattern.

Foi is the 3rd person singular of the preterite of ser.

Here it means was:

• A ocorrência foi grave = The occurrence was serious

This is the simple past, used for something seen as a completed event or fact.

A learner should also know that foi can also be the preterite of ir (went), but in this sentence it can only mean was, because it is followed by the adjective grave, not a destination.

This is a very common question.

• foi = was in the preterite, presenting the event as a completed fact
• era = was in the imperfect, often used for background description, ongoing past states, or habitual situations

In A ocorrência foi grave, the speaker is making a clear, finished assessment of the incident: it was serious.

If you said A ocorrência era grave, it would sound less natural in most contexts, unless you were describing the situation in progress or as background in a larger narrative.

So in reports, summaries, and factual statements, foi grave is the more natural choice.

Because grave here describes the nature or seriousness of the incident, not a temporary condition in the usual estar sense.

Portuguese often uses:

• ser for classification, identity, or essential characterization
• estar for temporary states or conditions

An incident being grave is treated as a characteristic judgment about it, so:

• A ocorrência foi grave = the incident was serious

Using esteve grave would sound unusual here. It might fit better with a person or medical condition, for example:

• O doente esteve grave = The patient was in a serious condition

But for an event or incident, foi grave is the normal choice.

Because grave is an adjective with the same form for masculine and feminine singular.

Compare:

• o caso grave = the serious case
• a ocorrência grave = the serious occurrence

Only the plural changes:

• os casos graves
• as ocorrências graves

So even though ocorrência is feminine, grave stays grave in the singular.

Not exactly.

Ocorrência is a broader and often more formal word. Depending on context, it can mean:

• occurrence
• incident
• event
• case
• reported occurrence

In Portugal, it is common in official, police, administrative, or news-style language.

So:

• A ocorrência foi grave sounds rather formal, like something from a report or official statement.
• In everyday speech, people might sometimes prefer more specific words like acidente, incidente, or caso, depending on what actually happened.

Normally, no. In standard Portuguese, you would usually need the article here:

• A ocorrência foi grave

Without the article, Ocorrência foi grave sounds incomplete or unnatural in ordinary speech and writing.

You might occasionally see article omission in very abbreviated styles, such as headlines, notes, or bureaucratic shorthand, but it is not the normal full sentence form.

It is natural, but it sounds fairly formal or official.

A native speaker might use it in contexts like:

• a police report
• a news report
• an official statement
• formal written communication

In casual conversation, someone might choose a more everyday phrasing, depending on context, such as:

• Foi grave.
• O incidente foi grave.
• O acidente foi grave.

So the sentence is perfectly correct, but the noun ocorrência gives it a more institutional or report-like tone.

In European Portuguese, ocorrência is pronounced approximately like:

oh-koh-RRÊN-syah

A few useful points:

• the rr is a strong r sound
• the stress falls on rên
• the ending -cia sounds like syah

And the whole sentence:

A ocorrência foi grave.

roughly sounds like:

uh oh-koh-RRÊN-syah foy GRAH-v(uh)

In European Portuguese, unstressed vowels are often reduced, so the final -e in grave is very light.