Il vaut mieux prendre un parapluie quand l’orage arrive.

In il vaut mieux, the il is an impersonal subject. It does not mean he or it in the usual sense. English does something similar with expressions like it is better to...

So:

• Il vaut mieux prendre un parapluie = It is better to take an umbrella
• More naturally: You’d better take an umbrella

The expression valoir mieux means to be better or to be preferable.

Vaut is the 3rd person singular form of the verb valoir (to be worth / to be better in some expressions).

• valoir → il vaut
• veut comes from vouloir (to want), so that would be a completely different verb.

Also, after il vaut mieux, French normally uses an infinitive directly, without de:

• Il vaut mieux prendre un parapluie.
• not Il vaut mieux de prendre...

So the pattern is:

• Il vaut mieux + infinitive

Example:

• Il vaut mieux partir tôt. = It’s better to leave early.

Because it follows the structure il vaut mieux + infinitive.

French often uses an infinitive after expressions like this, just as English does in it’s better to take...

So:

• Il vaut mieux prendre = It is better to take
• Il vaut mieux attendre = It is better to wait

You are not saying someone takes; you are talking about the general action to take.

Un parapluie means an umbrella or a umbrella / some umbrella in general. It is indefinite.

That makes sense here because the sentence is giving general advice:

• take an umbrella

If you said le parapluie, it would sound more like a specific umbrella already known in context:

• Take the umbrella = a particular one

So:

• un parapluie = any umbrella / an umbrella
• le parapluie = the umbrella

In French, after quand referring to the future, the verb is often in the present tense, where English would often use a future form.

So French says:

• quand l’orage arrive

But English often says:

• when the storm arrives
• or when the storm comes

French does not usually say quand l’orage arrivera in a sentence like this, even though the meaning is future.

This is a very important difference from English.

Because orage begins with a vowel sound, and French usually uses elision:

• le + orage → l’orage

This is very common:

• le ami → l’ami
• la école → l’école
• je ai → j’ai

So l’orage simply means the storm / thunderstorm.

Orage usually means a thunderstorm rather than just any kind of storm.

So in many contexts:

• orage = thunderstorm
• tempête = storm, often a stronger or more general storm, especially with wind

Depending on the translation shown to the learner, orage might be rendered as storm, but its core meaning is often closer to thunderstorm.

Yes, you could say Il faut prendre un parapluie, but the meaning changes slightly.

• Il vaut mieux prendre un parapluie = It’s better to take an umbrella / You’d better take an umbrella
• Il faut prendre un parapluie = You must / need to take an umbrella

So:

• il vaut mieux gives advice or says what is preferable
• il faut expresses necessity

The original sentence sounds a bit softer and more natural as advice.

Yes. It can also be followed by que + subjunctive when you name who should do the action.

Compare:

• Il vaut mieux prendre un parapluie.
  = It’s better to take an umbrella.

• Il vaut mieux que tu prennes un parapluie.
  = It’s better that you take an umbrella.

So:

• Il vaut mieux + infinitive = general statement
• Il vaut mieux que + subject + subjunctive = specific person mentioned

That is why the original sentence uses the infinitive: it gives general advice.

French often uses the present tense in time clauses to refer to future events, especially after words like:

• quand = when
• dès que = as soon as
• lorsque = when

So quand l’orage arrive literally looks like when the storm arrives/is arriving, but it naturally refers to a future moment.

This is normal French grammar, not a mistake.

Yes, it is very natural.

In French, prendre is commonly used where English uses take:

• prendre un taxi = take a taxi
• prendre un café = have/take a coffee
• prendre un parapluie = take an umbrella

Depending on context, French could also use emmener or apporter, but prendre un parapluie is a very normal and idiomatic choice for general advice.

A careful pronunciation is roughly:

Il vaut mieux prendre un parapluie quand l’orage arrive.
eel voh myuh prahndr uh(n) pah-rah-plwee kahn loh-rahzh ah-reev

A few useful points:

• mieux sounds like myuh
• prendre has a nasal vowel; the final -re is not strongly pronounced
• un has a nasal vowel, not like English un
• l’orage links smoothly because of the elision
• quand is nasal, roughly kahn

Pronunciation varies a bit by accent, but those are the main features.

Yes, absolutely. That version is also correct and very natural:

• Quand l’orage arrive, il vaut mieux prendre un parapluie.

French often allows this kind of reordering when one part is a time clause.

The difference is mainly one of emphasis:

• Il vaut mieux prendre un parapluie quand l’orage arrive.
  Focus starts with the advice.

• Quand l’orage arrive, il vaut mieux prendre un parapluie.
  Focus starts with the situation or time.

Both are correct.