Eu vou te avisar quando a reunião terminar.

Yes, you can usually leave eu out.

Portuguese often drops subject pronouns because the verb form already shows who the subject is. So:

• Eu vou te avisar...
• Vou te avisar...

Both are natural and mean the same thing.

Including eu can add a little emphasis, contrast, or clarity. For example, you might say Eu vou te avisar if you want to stress that I will be the one informing you.

Vou avisar is a very common way to express the future in Brazilian Portuguese.

Literally, vou means I go, but vou + infinitive works like I’m going to... or often simply I will... in English.

So:

• vou avisar = I’m going to let you know / I’ll let you know

This is one of the most common future patterns in everyday Brazilian Portuguese, often more common in speech than the simple future form.

For example:

• Eu vou ligar amanhã. = I’ll call tomorrow.

Te means you as the object of the verb.

In Eu vou te avisar, the person doing the action is eu = I, and the person receiving the action is te = you.

So the structure is:

• eu = I
• te = you
• avisar = inform / let know

Together: I will let you know

A native English speaker may expect something more like avisar você, and that is possible too. But te is very common and natural in Brazilian Portuguese when speaking informally to one person.

Because object pronouns like te usually go before the infinitive in this kind of Brazilian Portuguese structure.

So the natural order is:

• vou te avisar

not usually:

• vou avisar te

You may also see avisar-te, especially in more formal writing or in European Portuguese, but in everyday Brazilian Portuguese, vou te avisar sounds much more natural.

It can mean either one depending on context, but here it means something like to let someone know or to inform.

In this sentence, avisar is not really a warning. It is simply telling someone something when the time comes.

So good English equivalents here are:

• I’ll let you know
• I’ll tell you
• I’ll inform you

If the context were different, avisar could sound more like warn, but that is not the most natural meaning here.

Because reunião is a feminine noun in Portuguese, so it takes the feminine singular definite article a.

• a reunião = the meeting

If the noun were masculine, you would use o instead.

Examples:

• a reunião = the meeting
• o evento = the event

This is just part of learning each noun together with its gender.

In this sentence, terminar is functioning as the future subjunctive, not as a plain infinitive.

After words like quando, Portuguese often uses the future subjunctive to talk about something that will happen in the future but has not happened yet.

So:

• quando a reunião terminar = when the meeting ends / when the meeting is over

The tricky part is that for many regular verbs, the future subjunctive looks exactly the same as the infinitive. That is why terminar may look like just the dictionary form.

Compare with an irregular verb, where the form is easier to recognize:

• quando eu for = when I go
• quando ele tiver = when he has

So in your sentence, terminar is best understood as a future-time clause: when the meeting is finished.

Because that would mean something different.

• quando a reunião terminar = when the meeting ends / once the meeting is over
• quando a reunião vai terminar = when the meeting is going to end or what time the meeting will end

The sentence you have is about notifying someone after the meeting is finished.

If you say quando a reunião vai terminar, you are talking about the expected ending time, not the moment after it actually ends.

So for this meaning, quando a reunião terminar is the right structure.

Sometimes you may hear the present tense used in casual speech, but quando a reunião terminar is the more standard and precise choice for a future situation like this.

Using terminar here clearly marks the idea:

• the meeting has not ended yet
• when it does end, I will let you know

So for learners, quando + future subjunctive is the safest and best pattern to use in sentences like this.

Traditionally, te is associated with tu, but in Brazilian Portuguese, many speakers use te very naturally even when they use você as the subject form.

So in real Brazilian usage, combinations like these are very common:

• Você, eu te aviso depois.
• Eu vou te ligar.

This kind of mixing is normal in many parts of Brazil.

If you want a very neutral everyday sentence, vou te avisar is perfectly natural.

Yes. Portuguese allows some flexibility.

For example:

• Eu vou te avisar quando a reunião terminar.
• Quando a reunião terminar, eu vou te avisar.
• Te aviso quando a reunião terminar.

All of these are natural, though they have slightly different rhythm or emphasis.

The original version is very common and straightforward: first the main action, then the time clause.

Both can refer to the future, but they feel a little different.

• Eu vou te avisar sounds like I will / I’m going to let you know
• Eu te aviso can also mean I’ll let you know, especially in conversational Portuguese

In many everyday situations, both are natural.
However, vou + infinitive makes the future meaning more explicit, which is often helpful for learners.

So the original sentence is a very clear and common way to say it.