Se começar outro temporal, vamos ficar em casa.

In this sentence, começar is functioning as the future subjunctive, not the infinitive, even though the form looks the same.

After se meaning if, Portuguese often uses the future subjunctive when talking about a possible future event:

• Se chover, ficamos em casa.
• Se ele vier, eu aviso.
• Se começar outro temporal, vamos ficar em casa.

With many -ar verbs, the future subjunctive looks exactly like the infinitive:

• infinitive: começar
• future subjunctive: quando/se eu começar, você começar, ele começar...

So learners often think it is just an infinitive, but grammatically it is the tense/mood used for a future possibility after se.

A helpful comparison:

• Se ele vier... → clearly future subjunctive
• Se começar... → same idea, but the form happens to match the infinitive

Both are correct, but vamos ficar is usually more natural and common in everyday Brazilian Portuguese.

Two ways to talk about the future:

• vamos ficar em casa = we’re going to stay home
• ficaremos em casa = we will stay home

In Brazil, the ir + infinitive future is extremely common in speech. It often sounds more natural and conversational.

So:

• Se começar outro temporal, vamos ficar em casa. → very natural in spoken Brazilian Portuguese
• Se começar outro temporal, ficaremos em casa. → correct, but a bit more formal or written

Because this sentence is expressing a real future possibility, not a hypothetical or unlikely condition.

• Se começar outro temporal, vamos ficar em casa.
  = If another storm starts, we’ll stay home.

This is a normal future condition.

Ficaríamos would usually appear in a different kind of structure, often with the imperfect subjunctive:

• Se começasse outro temporal, ficaríamos em casa.
  = If another storm were to start / if another storm started, we would stay home.

So the pairing is usually:

• se + future subjunctive → future / present
• se + imperfect subjunctive → conditional

In this sentence, temporal does not mean related to time.

In Brazilian Portuguese, um temporal means something like:

• a storm
• a heavy rainstorm
• a severe downpour
• bad weather with strong rain, wind, thunder, etc.

So outro temporal means another storm or another heavy rainstorm.

This is a very common false friend for English speakers, because English temporal usually relates to time.

Both can exist, but outro temporal is very natural here.

In Portuguese, outro can often appear without an article:

• Quero outro café.
• Vamos escolher outra opção.
• Se começar outro temporal...

Adding um is possible in some contexts, but it can sound more specific or more marked:

• Se começar um outro temporal...

In this sentence, outro temporal sounds simpler and more idiomatic.

Em casa is the standard expression for at home or home in a general sense.

• Estou em casa. = I’m at home.
• Vamos ficar em casa. = We’re going to stay home.

Use na casa when you mean in/at someone’s house or a specific house:

• Estou na casa da minha avó. = I’m at my grandmother’s house.
• Eles estão na casa nova. = They are in the new house.

So:

• em casa = at home
• na casa = in the house / at someone’s house / at a specific house

The comma separates the if-clause from the main clause:

• Se começar outro temporal, = if another storm starts
• vamos ficar em casa. = we’re going to stay home

This is also common in English:

• If it starts storming again, we’ll stay home.

In Portuguese, when the se clause comes first, using a comma is standard.

If the main clause comes first, the comma is often omitted:

• Vamos ficar em casa se começar outro temporal.

Yes. That would also be very natural, but it changes the nuance a little.

• Se começar outro temporal...
  suggests another storm/heavy rainstorm starting
• Se chover de novo...
  simply means if it rains again

So temporal sounds stronger and more dramatic than just chover.

Examples:

• Se chover de novo, vamos ficar em casa. = If it rains again, we’ll stay home.
• Se começar outro temporal, vamos ficar em casa. = If another storm starts, we’ll stay home.

No. In Portuguese, this kind of structure is normal and natural.

Literally, começar outro temporal is another storm starts / begins.

Portuguese often allows this kind of construction without adding an extra subject like it. English usually needs it in weather expressions, but Portuguese often does not.

Compare:

• English: If it starts raining...
• Portuguese: Se começar a chover...

And with temporal:

• Se começar outro temporal... = If another storm starts...

So this sounds complete and idiomatic in Portuguese.

Yes. That would mean If a storm starts or If a storm begins.

The difference is:

• um temporal = a storm
• outro temporal = another storm

So outro implies there has already been one before, or the speaker expects a repeat.

Compare:

• Se começar um temporal, vamos ficar em casa.
  If a storm starts, we’ll stay home.
• Se começar outro temporal, vamos ficar em casa.
  If another storm starts, we’ll stay home.

A natural Brazilian Portuguese pronunciation would sound roughly like:

Se comeSAHR ôtru tempohRAU, vamu fihKAHR en KAHza.

A few useful points:

• começar is stressed on the last syllable: co-me-ÇAR
• outro in Brazil is often pronounced closer to ôtru
• temporal is stressed on the last syllable: tem-po-RAL
• vamos in casual speech may sound like vamu(s)
• em casa often sounds like en casa

You do not need to pronounce every word exactly as written in a slow, careful way to sound natural.

Yes. The most common alternative is:

• Vamos ficar em casa se começar outro temporal.

This means the same thing:

• If another storm starts, we’re going to stay home.

The version with se first is often used when the condition is being emphasized:

• Se começar outro temporal, vamos ficar em casa.

The version with the main clause first can sound a bit more straightforward:

• Vamos ficar em casa se começar outro temporal.

Both are correct and natural.