Se eu sair sem o guarda-chuva, vou correr o risco de ficar molhado.

Because after se when you are talking about a possible future situation, Portuguese normally uses the future subjunctive.

• Se eu sair... = If I go out / if I leave
• This refers to something that may happen later.

Compare:

• Se eu saio, ... → this sounds wrong in standard Portuguese for this future meaning.
• Se eu sair, ... → correct for a future possibility.

This is one of the most important patterns in Portuguese:

• Se eu tiver tempo... = If I have time...
• Se ele puder... = If he can...
• Se nós formos... = If we go...

So in this sentence, sair is the future subjunctive form of sair.

For many verbs, especially regular ones and some irregular ones, the future subjunctive looks identical to the personal infinitive or even the plain infinitive in some forms.

With sair, the form for eu is:

• infinitive: sair
• future subjunctive: quando/se eu sair

So even though it looks like the infinitive, its function is different here.

You can tell it is the future subjunctive because of the structure:

• Se eu sair...

That structure strongly signals a conditional future idea.

It can mean either, depending on context.

In this sentence:

• Se eu sair sem o guarda-chuva...

the most natural English idea is usually:

• If I go out without the umbrella or
• If I leave without the umbrella

Both fit. Sair often means physically going out, leaving a place, or heading out.

Because Portuguese often uses the definite article where English would not.

• sem o guarda-chuva literally = without the umbrella
• But in natural English, this may mean without my umbrella or without the umbrella

The article o often points to a specific, context-known object. In real life, that usually means the umbrella the speaker would normally take.

Compare:

• sem o guarda-chuva = without the umbrella / without my umbrella / without that umbrella
• sem um guarda-chuva = without an umbrella, without any umbrella

So sem o guarda-chuva sounds like there is a particular umbrella in mind.

Literally, guarda-chuva is something like rain-protector or that which guards against rain.

It is a compound noun:

• guardar = to keep/protect
• chuva = rain

But you should just learn it as the normal word for umbrella.

Also note:

• it is masculine: o guarda-chuva
• the plural is usually os guarda-chuvas

It means I’m going to run the risk of or more naturally I’ll risk / I may end up risking.

The full expression is:

• correr o risco de + infinitive

Examples:

• correr o risco de perder = to run the risk of losing
• correr o risco de errar = to risk making a mistake
• correr o risco de ficar molhado = to run the risk of getting wet

It is a fixed expression, so it is best learned as a chunk.

Because the expression is:

• correr o risco de + infinitive

So the de belongs to the construction itself.

You cannot normally say:

• correr o risco ficar molhado ❌

You need:

• correr o risco de ficar molhado ✅

This is similar to how some English expressions require a certain preposition, even if it does not translate word-for-word.

Because in Brazilian Portuguese, ir + infinitive is very common for future meaning, especially in everyday speech.

• vou correr o risco = I’m going to run the risk / I will risk
• correrei o risco = I will run the risk

Both are grammatically possible, but vou correr sounds more natural and conversational in most spoken Brazilian Portuguese.

This pattern is extremely common:

• vou sair = I’m going to leave
• vou fazer = I’m going to do
• vou ver = I’ll see

It means to get wet or to end up wet.

Here, ficar means to become or to end up in a state.

So:

• ficar molhado = become wet / get wet

Compare:

• estar molhado = to be wet
• ficar molhado = to get wet

That is why ficar is a good choice here: the speaker is talking about the result of going out without the umbrella.

Because adjectives in Portuguese agree with the person or thing they describe.

Here, molhado refers to eu. If the speaker is male, molhado is correct. If the speaker is female, it would normally be:

• Se eu sair sem o guarda-chuva, vou correr o risco de ficar molhada.

So:

• molhado = masculine
• molhada = feminine

This is a very common thing in Portuguese that English speakers need to watch for.

It is standard and helpful.

• Se eu sair sem o guarda-chuva, vou correr o risco de ficar molhado.

The comma separates the conditional clause from the main clause:

• Se eu sair sem o guarda-chuva = if I go out without the umbrella
• vou correr o risco de ficar molhado = I’ll run the risk of getting wet

In writing, this comma is normal and recommended.

Yes, but the meaning shifts slightly.

• sem o guarda-chuva = without the umbrella / without my umbrella / without the specific umbrella
• sem um guarda-chuva = without an umbrella, without any umbrella

So both are possible, but they do not sound exactly the same.

If the situation is about your usual umbrella, or a specific umbrella already understood in context, o guarda-chuva is very natural.

Yes, it is common and natural, though depending on tone, Brazilians might also say simpler alternatives.

For example:

• vou correr o risco de ficar molhado = I’ll run the risk of getting wet
• posso ficar molhado = I might get wet
• vou acabar ficando molhado = I’ll end up getting wet

Your original sentence is perfectly natural, but it sounds a little more explicit and slightly more formal than the shortest everyday option.

Yes. Molhado/molhada can describe a person, clothing, hair, the ground, and many other things.

Examples:

• Estou molhado. = I’m wet.
• A camisa está molhada. = The shirt is wet.
• O chão ficou molhado. = The floor got wet.

So in your sentence, ficar molhado naturally means the speaker would get wet.

It is natural and correct.

• Se eu sair sem o guarda-chuva, vou correr o risco de ficar molhado.

A Brazilian speaker would understand it easily. In casual conversation, though, many people might choose a slightly simpler version, such as:

• Se eu sair sem o guarda-chuva, posso ficar molhado.
• Se eu sair sem guarda-chuva, vou me molhar.

But your sentence is absolutely good Portuguese and sounds clear and idiomatic.