Mwezi wa Juni ulikuwa na mvua nyingi, lakini Julai ulileta baridi kali zaidi asubuhi.

Here wa is the associative/genitive connector, often translated as of. So Mwezi wa Juni means the month of June.

It changes form to agree with the noun before it. Because mwezi is a class 3 noun, the connector is wa here.

Because the second mwezi wa is understood and does not need to be repeated.

So:

• Mwezi wa Juni ulikuwa na mvua nyingi
• lakini Julai ulileta baridi kali zaidi asubuhi

is essentially the same as:

• Mwezi wa Juni ulikuwa na mvua nyingi, lakini mwezi wa Julai ulileta baridi kali zaidi asubuhi

This kind of omission is very natural in Swahili when the meaning is already clear.

Because both verbs agree with mwezi — either stated directly (Mwezi wa Juni) or understood (Julai = mwezi wa Julai).

You can break uli- down like this:

• u- = subject marker for noun class 3 singular
• -li- = past tense marker

So:

• u-li-kuwa = it was
• u-li-leta = it brought

The it here refers to the month.

In Swahili, kuwa na literally means to be with, but it is also the normal way to say to have.

So:

• ulikuwa na mvua nyingi literally = it was with much rain
• natural English = it had a lot of rain

This is a very common Swahili pattern:

• nina kitabu = I have a book
• alikuwa na pesa = he/she had money

Because nyingi must agree with mvua.

The adjective stem is -ingi, meaning many / much / a lot of. With mvua, it becomes nyingi.

So:

• mvua nyingi = a lot of rain / many rains

This can feel slightly unusual to an English speaker because English distinguishes much rain and many rains/showers, but Swahili simply uses the agreeing form nyingi here.

Yes. It is natural to let a month or season act as the subject of a verb like leta (bring).

So Julai ulileta baridi... means that July brought, caused, or came with colder conditions.

It is similar to English expressions like:

• Winter brought heavy winds
• March brought warmer days

This phrase is built in layers:

• baridi = cold / cold weather
• kali = strong, harsh, intense
• zaidi = more

So baridi kali zaidi means something like:

• more intense cold
• harsher cold
• in natural English, often simply colder weather

A key point is that Swahili does not always use a single comparative adjective the way English does. Instead, it often builds the idea with words like kali and zaidi.

Because the thing being compared is already clear from the context: July is being compared with June.

So zaidi on its own is enough here to mean more.

If you wanted to make the comparison fully explicit, you could add kuliko Juni:

• Julai ulileta baridi kali zaidi kuliko Juni asubuhi

But in the original sentence, that would sound a bit more repetitive because June has already just been mentioned.

Asubuhi means in the morning / mornings here.

It comes at the end because it functions as a time expression modifying the second part of the sentence:

• Julai ulileta baridi kali zaidi asubuhi
  = July brought harsher cold in the morning

Swahili often places time expressions at the end, though they can also be moved for emphasis.

Also, in context, asubuhi does not have to mean one single morning. It can refer more generally to morning time or mornings.

Yes, absolutely.

Using the month name alone is very common:

• Juni ulikuwa na mvua nyingi
• Julai ulileta baridi kali zaidi asubuhi

Adding Mwezi wa is just more explicit. It can sound slightly fuller or more formal, especially on first mention. After that, speakers often switch to just the month name.