tokuni natu ha yokusitu ni mado ga nai to, sugu atuku narimasu.

は marks 夏 as the topic or setting: as for summer / especially in summer.

So とくに 夏 は gives the idea of:

• especially in summer
• when it comes to summer in particular

It is not simply marking time in the same way English uses in. Japanese often uses は to set the scene or contrast one situation with others.

とくに means especially or particularly.

It emphasizes that the statement is even more true in one case than in others. Here it highlights summer:

• とくに 夏 は = especially in summer

So the speaker implies that the bathroom can get hot in general, but this is particularly noticeable in summer.

Here, に marks the location where something exists or does not exist.

• 浴室に窓がある = There is a window in the bathroom
• 浴室に窓がない = There is no window in the bathroom

This is the normal pattern with ある / ない:

• place + に + thing + が + ある / ない

By contrast, で usually marks the place where an action happens. Since ない here is not an action but a state of non-existence, に is the natural choice.

が is the standard particle for the thing that exists or does not exist with ある / ない.

So:

• 窓がない = there is no window

If you said 窓はない, it would sound more contrastive, like:

• As for windows, there aren't any
• There isn't a window, though maybe something else is there

In this sentence, the plain descriptive form 窓がない is the most natural.

Here と is a conditional particle meaning something like:

• if
• when
• whenever

So:

• 窓がないと、すぐ暑くなります
• If there is no window, it gets hot quickly

This と is often used for results that are natural, automatic, or generally true. It can sound like whenever X happens, Y happens.

In this sentence, the idea is that lacking a window naturally leads to the bathroom heating up quickly.

No. In this sentence, ないと is just:

• ない + と
• if there is not ...

So 窓がないと means if there is no window.

This is different from conversational patterns like:

• 行かないと = I have to go

That have to meaning comes from a different ellipsis pattern and is not what is happening here.

Because なる combines with the adverbial form of an い-adjective.

Pattern:

• 暑い → 暑くなる = become hot
• 寒い → 寒くなる = become cold
• 早い → 早くなる = become early / faster

So:

• 暑くなります = becomes hot / gets hot

This is a very common grammar pattern.

なります is the polite present/future form of なる.

• なる = plain form
• なります = polite form

Japanese teaching materials and everyday polite conversation often use ます forms, so this sentence sounds polite and neutral.

すぐ means soon, right away, or quickly, depending on context.

Here it means the bathroom quickly becomes hot once there is no window for ventilation.

So すぐ暑くなります is:

• it gets hot quickly
• it soon becomes hot

Yes, the subject is not stated explicitly, which is very normal in Japanese.

From context, the thing becoming hot is understood to be the bathroom / the bathroom space.

Japanese often leaves out subjects when they are obvious from context. In English, we usually need to supply one, but Japanese often does not.

Japanese often puts the broader setting or topic early in the sentence.

So the structure is roughly:

• As for summer especially, if there is no window in the bathroom, it gets hot quickly.

Putting とくに 夏 は near the beginning helps establish the context first. That is very natural in Japanese.

Yes, but more literally 浴室 refers to the bath room / bathing room, especially the room with the tub or shower.

Depending on context, English may translate it as:

• bathroom
• bath area
• bath/shower room

If the full English meaning has already been given to the learner, the important point is that 浴室 refers specifically to the bathing space, not necessarily the entire restroom area.

It sounds like a general fact or a habitual tendency.

That comes mainly from:

• the conditional と
• the non-past polite form なります

So the sentence means something like:

• If a bathroom doesn’t have a window, it gets hot quickly, especially in summer.

It is not describing just one specific occasion unless the wider context makes it specific.