Usipoivaa skafu yako asubuhi, utahisi baridi.

It is made of several parts:

• u- = you (singular)
• -si- = negative
• -po- = if/when
• -i- = it (object marker)
• vaa = wear / put on

So usipoivaa literally means if you do not wear it.

In this sentence, it refers to skafu yako (your scarf).

Because Swahili usually puts the subject inside the verb.

• u- in usipoivaa = you
• uta- in utahisi = you will

So Swahili does not need a separate subject pronoun the way English does.
You could add wewe for emphasis, but it is not necessary:

• Wewe usipoivaa skafu yako asubuhi, utahisi baridi.

That would sound more like you, if you don’t wear your scarf in the morning, you’ll feel cold.

Here -po- marks a dependent clause and often has the sense of if or when.

In this sentence, the most natural translation is if:

• Usipoivaa skafu yako asubuhi...
• If you don’t wear your scarf in the morning...

In other contexts, -po- can be closer to when, especially if the speaker sees the event as likely or expected. So it is a flexible marker, and context tells you which English word fits best.

That -i- is the object marker, meaning it.

It refers to skafu, which is a class 9 noun in the singular.
So:

• usipovaa = if you do not wear
• usipoivaa = if you do not wear it

Since the object is the scarf, the sentence uses -i- to refer back to it.

Yes. That is also a normal and understandable sentence.

• Usipovaa skafu yako asubuhi, utahisi baridi.
• Usipoivaa skafu yako asubuhi, utahisi baridi.

Both work. The version with -i- makes the object a little more explicit or definite: if you don’t wear it, your scarf...
Because the object is already stated right after the verb, some speakers may omit the object marker, while others keep it. Both patterns are common.

Because skafu belongs to noun class 9 in the singular, and the possessive has to agree with that noun class.

The possessive stem for your is -ako, and class 9 uses the agreement ya-, so:

• ya + ako = yako

So:

• skafu yako = your scarf

If it were plural, it would be:

• skafu zako = your scarves

Because Swahili often uses time words directly, without a preposition.

So:

• asubuhi = in the morning / this morning
• jioni = in the evening
• usiku = at night

You do not need a separate word for in here.
That is why skafu yako asubuhi naturally means your scarf in the morning.

Utahisi breaks down like this:

• u- = you
• -ta- = future
• hisi = feel

So utahisi means you will feel.

Then baridi means cold or coldness. After hisi, it works as the thing being felt:

• utahisi baridi = you will feel cold

Swahili does not need an extra word like be here.
English says feel cold, and Swahili does the same kind of thing.

Here baridi means the sensation of being cold.

It can also refer more generally to cold weather or coldness, depending on context. In this sentence, the meaning is clearly the physical feeling:

• utahisi baridi = you will feel cold

So it is not talking about a disease like a cold. It is talking about temperature and bodily sensation.

Yes. Swahili can also put the main clause first:

• Utahisi baridi usipoivaa skafu yako asubuhi.

This still means the same thing.
The original version puts the condition first, which is very natural in warnings and advice:

• If you don’t wear your scarf in the morning, you’ll feel cold.

So the original order sounds like a clear caution.

A simple pronunciation guide is:

• Usipoivaa = u-see-po-ee-vaa
• skafu = ska-foo
• yako = ya-ko
• asubuhi = a-su-boo-hee
• utahisi = u-ta-hee-see
• baridi = ba-ree-dee

A few helpful points:

• Swahili vowels are usually pronounced clearly and consistently.
• vaa has a long aa sound.
• Stress is usually on the second-to-last syllable.

So the rhythm is roughly:

u-si-po-i-VAA SKA-fu YA-ko a-su-BU-hi u-ta-HI-si ba-RI-di