Kung malakas ang ulan, huwag kang lumabas.

Kung introduces a condition, so it means if here.

You can sometimes use kapag, but there is a nuance:

• kung = if
• kapag = when / whenever, often for something expected or repeated

So:

• Kung malakas ang ulan, huwag kang lumabas. = If the rain is heavy, don’t go out.
• Kapag malakas ang ulan, huwag kang lumabas. = When(ever) the rain is heavy, don’t go out.

In everyday speech, the two often overlap, but kung is the most straightforward choice for a plain condition.

In Filipino, weather intensity is often described with malakas, which literally means strong.

So:

• malakas ang ulan = the rain is strong = the rain is heavy / it is raining hard

This is natural Filipino usage. English says heavy rain, but Filipino commonly says strong rain.

A learner might think of malaki because English says heavy or because rain can seem like a “big” event, but malaki ang ulan is not the normal way to say this.

Ang marks the noun that is being talked about as the topic of the sentence.

In malakas ang ulan:

• malakas = heavy/strong
• ang ulan = the rain

So the structure is literally something like:

• Heavy/strong is the rain

Natural English rearranges that as:

• The rain is heavy
• It is raining hard

So ang is not exactly the same as the in English. It is a grammatical marker, not just an article.

Both are correct, but malakas ang ulan is the more natural, everyday order.

Filipino often puts the predicate first. So:

• Malakas ang ulan. = natural, common
• Ang ulan ay malakas. = also correct, but more formal, deliberate, or explanatory

This predicate-first pattern is very common in Tagalog/Filipino.

Filipino does not need a dummy subject like English it in weather expressions.

English says:

• If it is raining hard...

But Filipino can say:

• Kung malakas ang ulan...

There is no need for a word corresponding to that English it. Instead, Filipino simply talks directly about ulan (rain).

Huwag is used to make a negative command, so it means don’t.

Examples:

• Huwag kang lumabas. = Don’t go out.
• Huwag kayong maingay. = Don’t be noisy.

Yes, 'wag or wag is the casual spoken/written form of huwag. They mean the same thing.

• Huwag kang lumabas. = standard spelling
• 'Wag kang lumabas. = casual spelling

The pronoun is ka (you, singular), but here it becomes kang because of the linker -ng.

So:

• ka = you
• ka + -ng = kang

This linker smoothly connects ka to the following word or phrase:

• huwag kang lumabas

A useful way to think of it is:

• huwag = don’t
• ka = you
• -ng = linker
• lumabas = go out

So the sentence is addressed to one person: don’t you go out / don’t go out.

This is a very common question.

Lumabas can indeed mean went out in a normal statement:

• Lumabas siya. = He/She went out.

But after huwag, the same form is understood differently. In this kind of construction, it works like go out / to go out in English:

• Huwag kang lumabas. = Don’t go out.

So the key point is:

• Filipino verb forms do not match English tense forms one-for-one.
• The surrounding construction matters.
• After huwag, lumabas is the normal form for a prohibition.

You may also hear Huwag kang lalabas, which is also used in real life and can sound more pointed or situational, but huwag kang lumabas is a very standard pattern for don’t go out.

Yes. Lumabas already contains the idea of go out / go outside / come out, depending on context.

So:

• lumabas = go out, step outside, exit

That is why no extra word for outside is necessary here.

Compare:

• lumabas = go out
• pumasok = go in
• umalis = leave, depart

In this sentence, lumabas is the best choice because the idea is specifically going outside into the heavy rain.

Yes. That is also correct and natural.

Both of these work:

• Kung malakas ang ulan, huwag kang lumabas.
• Huwag kang lumabas kung malakas ang ulan.

The difference is mostly in emphasis:

• Starting with kung... sets up the condition first.
• Starting with huwag kang lumabas... gives the command first.

The meaning stays the same.

You would change kang to kayong.

• Huwag kang lumabas. = Don’t go out. (to one person)
• Huwag kayong lumabas. = Don’t go out. (to more than one person, or polite singular)

So the full sentence becomes:

• Kung malakas ang ulan, huwag kayong lumabas.

In Filipino, kayo can also be used politely for one person.

In standard writing, a comma after the opening kung clause is a good idea:

• Kung malakas ang ulan, huwag kang lumabas.

It helps show that the first part is the condition and the second part is the main command.

In very casual writing or texting, people may leave it out, but the version with the comma is cleaner and more standard.