Ljeti je u gradu velika vrućina, pa radije ostajemo u sjeni.

Ljeti is an adverb meaning in summer or during the summer. It is a very common seasonal time expression in Croatian.

You can also hear u ljeto, but ljeti is shorter and very natural in everyday language.

Compare:

• Ljeti je vruće. = It’s hot in summer.
• Zimi pada snijeg. = It snows in winter.

So in your sentence, ljeti simply sets the time frame: in summer.

Je is the 3rd person singular present form of biti (to be). It matches vrućina, which is singular:

• vrućina = heat
• velika vrućina = great/intense heat

So the structure is basically:

• Ljeti je u gradu velika vrućina.
• In summer, there is great heat in the city.

Even though English might prefer it is very hot, Croatian often uses a noun phrase like velika vrućina.

Because u can mean in, and when it shows location, it takes the locative case.

• grad = city
• u gradu = in the city

This is a basic location pattern:

• u školi = in school
• u kući = in the house
• u gradu = in the city

If there were movement into the city, Croatian would normally use the accusative:

• Idem u grad. = I’m going to the city.

But here there is no movement, only location, so u gradu is correct.

Because vrućina is a feminine singular noun, so the adjective must agree with it in gender, number, and case.

• velik = masculine
• velika = feminine
• veliko = neuter

So:

• velika vrućina = correct
• veliko vrućina = incorrect

This kind of agreement is very important in Croatian.

Not quite.

• vrućina is a noun: heat
• vruće is usually an adverb/predicative form: hot

So:

• Velika je vrućina. = There is intense heat.
• Vruće je. = It is hot.

Both are natural, but they are built differently:

• noun-based expression: velika vrućina
• adjective/adverb-like expression: vruće

Here pa means something like so, therefore, or and so.

It connects the two ideas:

• it is very hot in the city in summer
• because of that, we prefer to stay in the shade

So:

• ..., pa radije ostajemo u sjeni.
• ..., so we prefer to stay in the shade.

In Croatian, pa is very common in everyday speech and can have slightly different shades of meaning depending on context.

Radije means rather / preferably. It is the comparative form of rado, which means gladly / willingly.

So:

• rado = gladly
• radije = rather, more willingly

Examples:

• Rado pijem čaj. = I gladly drink tea.
• Radije pijem čaj nego kavu. = I’d rather drink tea than coffee.

In your sentence, radije ostajemo u sjeni means we prefer to stay in the shade or more literally we rather stay in the shade.

This is a question of aspect, which is very important in Croatian.

• ostajati / ostati = to stay / remain
• ostajemo is from the imperfective verb ostajati
• ostanemo is from the perfective verb ostati

Here, the sentence describes a general habit or repeated behavior in summer, so the imperfective form is the natural choice:

• radije ostajemo u sjeni = we prefer to stay in the shade

Using ostanemo would sound more like a completed, one-time result in a specific situation, not a general habit.

Because Croatian usually drops subject pronouns when they are already clear from the verb ending.

• ostajemo already means we stay
• the ending -mo shows the subject is we

So mi is not necessary.

You can add mi for emphasis or contrast:

• Mi ostajemo u sjeni, a oni idu na sunce.
• We stay in the shade, and they go into the sun.

But in a neutral sentence, leaving out mi is more natural.

Sjeni is the locative singular of sjena (shade, shadow).

Because u means in here and shows location, it requires the locative:

• sjena = shade
• u sjeni = in the shade

This is parallel to:

• u sobi = in the room
• u vodi = in the water
• u školi = in school

So u sjeni is simply the normal way to say in the shade.

Croatian word order is fairly flexible, but the given order is very natural.

The sentence:

• Ljeti je u gradu velika vrućina, pa radije ostajemo u sjeni.

works well because it presents:

1. time: Ljeti
2. location: u gradu
3. main situation: velika vrućina
4. result/preference: pa radije ostajemo u sjeni

You could move some parts for emphasis, for example:

• U gradu je ljeti velika vrućina...
• Radije u sjeni ostajemo... (less neutral, more marked)

So the original version is a good standard model.

Yes, absolutely. That would also be a very natural sentence.

Compare:

• Ljeti je u gradu velika vrućina.

  • literally: In summer there is great heat in the city.
  • a bit more noun-based

• Ljeti je u gradu vrlo vruće.

  • In summer it is very hot in the city.
  • a bit more direct

Both are correct and idiomatic. The version with vrućina emphasizes the heat as a thing or condition, while vruće je simply describes the weather/feeling.

Yes, sjena can mean both shade and shadow, depending on context.

In this sentence:

• u sjeni clearly means in the shade

Because the context is summer heat, the meaning is not shadow in a dramatic or visual sense, but a shaded place out of the sun.

This phrase is very common:

• sjediti u sjeni = to sit in the shade
• ostati u sjeni = to stay in the shade