Aquesta tarda agafaré el metro perquè la meva tieta prepara una sorpresa per al meu oncle.

In Catalan, aquesta tarda works like an adverbial time expression, just like this afternoon in English. You do not need a preposition.

• aquesta tarda = this afternoon
• a la tarda = in the afternoon
• cada tarda = every afternoon

So Aquesta tarda agafaré el metro is perfectly natural.

Agafaré is the future tense of agafar.

It is formed by taking the infinitive agafar and adding the future ending -é:

• agafar
  • é → agafaré

This means I will take.

Some other future forms are:

• agafaràs = you will take
• agafarà = he/she/it will take
• agafarem = we will take
• agafareu = you all will take
• agafaran = they will take

Catalan usually drops subject pronouns when they are not needed, because the verb ending already shows who is doing the action.

So:

• agafaré already means I will take
• jo agafaré = I will take, with extra emphasis on I

In this sentence, jo is omitted because it is obvious from the verb.

Yes. Agafar el metro is a very common and natural way to say to take the metro in Catalan.

Examples:

• agafar el bus
• agafar el tren
• agafar un taxi

You may also hear prendre el metro in some contexts, but agafar is extremely common in everyday speech.

Catalan often uses the definite article with means of transport in expressions like this.

So:

• agafar el metro
• agafar el tren
• agafar l’autobús

This is very normal and does not sound unusually specific. It is simply the standard way to talk about taking that mode of transport.

Here perquè means because.

The accent matters, because Catalan distinguishes several similar-looking forms:

• perquè = because
• per què = why / for what reason
• el perquè = the reason

So in this sentence, perquè introduces the reason:

• agafaré el metro perquè... = I’ll take the metro because...

In Catalan, possessives are very often used with the definite article:

• la meva tieta = my aunt
• el meu oncle = my uncle
• el meu llibre = my book

This is one of the main differences from English. In English, you normally say my aunt without the. In Catalan, the article is usually included.

There are some special cases where the article may be omitted, but for a learner, article + possessive + noun is the safest and most natural pattern.

Tieta is related to tia.

• tia = aunt
• tieta = literally a diminutive, something like auntie or dear aunt

In many families and everyday speech, tieta is very natural and may simply be used where English would say aunt. It often sounds affectionate or familiar.

By contrast:

• oncle = uncle

Prepara is the present tense form of preparar: she prepares / is preparing.

Catalan, like English, often uses the present to talk about something that is:

• happening now
• already arranged
• understood as a current situation

So the sentence can suggest that the aunt is currently preparing the surprise, or that this is the present situation explaining why the speaker will take the metro.

If you changed it to prepararà, that would mean will prepare, which gives a different time sense.

Per al is the contraction of per a + el.

• per a = for
• el = the
• per al = for the

So:

• per al meu oncle = for my uncle

This structure is common when showing the intended recipient or purpose.

You may also hear some variation in everyday spoken Catalan depending on region and style, but per al meu oncle is fully standard.

Yes. The sentence can be reordered, especially if you want to emphasize the reason first.

For example:

• Perquè la meva tieta prepara una sorpresa per al meu oncle, aquesta tarda agafaré el metro.

This is grammatically possible, but the original order is more neutral and natural in many everyday contexts:

• Aquesta tarda agafaré el metro perquè la meva tieta prepara una sorpresa per al meu oncle.

That would also be possible in Catalan.

• agafaré = I will take
• vaig a agafar = I’m going to take

So:

• Aquesta tarda agafaré el metro
• Aquesta tarda vaig a agafar el metro

Both can refer to the future. The simple future agafaré is very common and straightforward here. The vaig a + infinitive form can sound a bit more like a planned or immediate future, depending on context.