Kalau hujan deras, saya bawa payung ke kantor.

In Indonesian, you usually do not need a dummy subject like English it in weather expressions.

So:

• It rains → Hujan
• It’s hot → Panas
• It’s cold → Dingin

That means Kalau hujan deras literally looks like If rain is heavy, but naturally it means If it rains heavily or When it rains hard.

Kalau can mean both if and when, depending on context.

In this sentence:

• Kalau hujan deras, saya bawa payung ke kantor.

it could mean:

• If it rains heavily, I bring an umbrella to the office
• When it rains heavily, I bring an umbrella to the office

Because Indonesian does not always force the same distinction English does, kalau is often flexible.

A few related words:

• kalau = common, everyday if/when
• jika = more formal if
• bila = also if/when, somewhat formal or literary

Because deras comes after hujan here.

In Indonesian, adjectives often come after the noun:

• rumah besar = big house
• air dingin = cold water
• hujan deras = heavy rain

So hujan deras is the normal order.

Also, in this sentence, hujan deras works like heavy rain / raining heavily.

Deras means something like heavy, strong, or intense for things that flow or fall.

Very common combinations are:

• hujan deras = heavy rain
• air mengalir deras = water flows strongly
• angin bertiup deras is less common than angin kencang, but understandable

So hujan deras is the natural way to say heavy rain.

Both are possible, but they feel a little different.

• saya membawa payung = more full/formal/standard
• saya bawa payung = very common in everyday speech and informal writing

Indonesian often drops the meN- prefix in casual language, especially when the subject is already clear.

So:

• Saya membawa payung ke kantor.
• Saya bawa payung ke kantor.

Both can mean I bring/take an umbrella to the office.

For learners, it is good to recognize both. If you want to sound more textbook-standard, use membawa. If you want to understand natural conversation, get used to hearing bawa.

It can be translated as either bring or take, depending on the point of view.

• bawa payung = bring/take an umbrella

English makes a stronger distinction between bring and take than Indonesian often does. Indonesian bawa/membawa mainly focuses on carrying something along.

So in this sentence, English could naturally be:

• I bring an umbrella to the office
• I take an umbrella to the office

Both are reasonable translations.

Because ke shows movement toward a destination, while di shows location.

• ke kantor = to the office
• di kantor = at the office / in the office

Since the sentence is about bringing an umbrella to the office, ke is the correct choice.

Compare:

• Saya bawa payung ke kantor. = I bring/take an umbrella to the office.
• Payung saya ada di kantor. = My umbrella is at the office.

Indonesian verbs do not change form for tense the way English verbs do, so the time meaning often comes from context.

This sentence most naturally sounds habitual or general:

• When/If it rains heavily, I bring an umbrella to the office.

It could also refer to a future situation if the context supports it, but by itself it feels like a general habit or rule.

If you wanted to make the future clearer, you could add a time word, for example:

• Kalau nanti hujan deras, saya akan bawa payung ke kantor.
  = If it rains heavily later, I’ll bring an umbrella to the office.

Yes. In Indonesian, this is natural.

Weather expressions often do not need an explicit subject, and the meaning is still complete:

• Kalau hujan... = If it rains...
• Kalau panas... = If it’s hot...
• Kalau macet... = If there’s traffic / If traffic is bad...

So even though English expects it, Indonesian does not.

Yes, that is also correct.

Both of these are natural:

• Kalau hujan deras, saya bawa payung ke kantor.
• Saya bawa payung ke kantor kalau hujan deras.

The difference is mostly about focus and flow:

• Starting with Kalau hujan deras highlights the condition first.
• Putting it at the end sounds a little more like I bring an umbrella to the office when it rains heavily.

Both are good.

Yes, it is natural, especially in everyday language. But native speakers might also say it in slightly different ways.

Common alternatives include:

• Kalau hujan deras, saya membawa payung ke kantor.
  More standard/formal

• Kalau hujan, saya bawa payung ke kantor.
  Simpler: If it rains, I bring an umbrella to the office

• Kalau lagi hujan deras, saya bawa payung ke kantor.
  More conversational: If it’s raining heavily, I bring an umbrella to the office

So your sentence is fine; it just uses a casual, common bawa instead of membawa.