Learn Hardcore Hausa: Yau rana ta fi jiya zafi. - Today is hotter than yesterday.

ta is the 3rd‑person singular feminine subject pronoun, and it agrees with rana ("day"), which is grammatically feminine in Hausa.
So rana ta fi … means "the day is more …".

If the subject were a masculine noun, you would use ya instead, for example:
Yau garin ya fi jiya zafi. – "Today the town is hotter than yesterday."

Why is there no word for "is" in this sentence?

Hausa often does not use a separate verb for "to be" in descriptive sentences. Here, ta fi itself functions as the verb and carries the meaning "is more than / exceeds".

Literally, Rana ta fi jiya zafi means "The day surpasses yesterday in heat", which we translate as "The day is hotter than yesterday." No extra "is" is needed.

Which word corresponds to English “than” in this sentence?

The comparative "than" idea is built into the verb fi.

The structure ta fi jiya zafi literally means:

ta fi jiya – "it surpasses yesterday"
zafi – "in heat / in hotness"

So instead of "hotter than yesterday", Hausa says "it surpasses yesterday in heat". There is no separate preposition like "than"; fi does that job.

What is the basic comparative pattern being used here?

The sentence follows a very common Hausa comparative pattern:

Subject + agreeing pronoun + fi + STANDARD + QUALITY

In Yau rana ta fi jiya zafi:

Subject: rana ("day")
Agreeing pronoun: ta
fi: "exceed / be more than"
STANDARD (the thing compared against): jiya ("yesterday")
QUALITY: zafi ("heat / hotness")

So structurally it matches English “X is hotter than Y”.

What is the role of yau at the beginning? Could it go somewhere else?

yau means "today" and functions as a time adverbial. It tells you when this statement is true.

Putting time words like yau ("today"), jiya ("yesterday"), gobe ("tomorrow") at the very start of the sentence is very typical in Hausa. It’s possible to move it (for example, Rana yau ta fi jiya zafi), but Yau rana ta fi jiya zafi is a very natural and common order.

Why do we need both yau and rana? Could I just say Yau ta fi jiya zafi?

In the full sentence, rana ("day") is the grammatical subject, and yau just specifies which day: "today’s day".

In everyday speech, many speakers do say simply:

Yau ta fi jiya zafi. – "Today is hotter than yesterday."

Here ta is a kind of "it" referring to the day/weather understood from context, and rana is left out.

For learners, Yau rana ta fi jiya zafi is clearer because you can directly see what ta agrees with.

Is zafi an adjective meaning “hot”, or something else?

zafi is actually a noun meaning "heat" or "hotness". Hausa very often uses such "quality nouns" where English uses adjectives.

So ta fi jiya zafi is literally "it exceeds yesterday (in) heat", but in natural English we say "it is hotter than yesterday."
Other examples with the same pattern:

Ali ya fi Musa tsawo. – "Ali is taller than Musa." (literally "Ali exceeds Musa (in) height.")
Wannan motar ta fi waccan kyau. – "This car is nicer than that one." (literally "...exceeds that one (in) beauty.")

Why is zafi at the end? Can I say Yau rana ta fi zafi jiya instead?

In this comparative pattern, the usual and natural order is:

Subject + pronoun + fi + STANDARD + QUALITY

So:

jiya (the standard of comparison) comes right after fi,
zafi (the quality) comes last.

That’s why ta fi jiya zafi is the normal order.
A version like *ta fi zafi jiya does not follow the standard pattern and would sound wrong or at least very odd to most speakers.

How can I say “much hotter than yesterday” using this structure?

You keep the same structure and add an intensifier after zafi. Common options include:

Yau rana ta fi jiya zafi sosai. – "Today is much hotter than yesterday."
Yau rana ta fi jiya zafi ƙwarai. – "Today is very / extremely hotter than yesterday."
Yau rana ta fi jiya zafi matuƙa. – "Today is extremely hotter than yesterday."

The intensifier normally comes after the quality word (zafi).

Are there other natural ways to say “Today is hotter than yesterday” in Hausa?

Yes, several, for example:

Yau zafi ya fi na jiya.
Literally: "Today, the heat is more than that of yesterday."
Yau rana ta yi zafi fiye da jiya.
Literally: "Today, the day did heat more than yesterday."
Yau akwai zafi fiye da jiya.
Literally: "Today there is heat more than yesterday."

All of these convey essentially the same idea; the original Yau rana ta fi jiya zafi is just a very compact fi-type comparative.

How would I say “Today is not hotter than yesterday” with the same structure?

To negate fi, you surround the pronoun + verb with ba … ba. A natural negation is:

Yau rana ba ta fi jiya zafi ba.
"Today is not hotter than yesterday."

Here:

ba … ba are the negative markers,
ta fi becomes ba ta fi … ba – "does not exceed / is not more than".

Why don’t we add ne or ce at the end, like Yau rana ta fi jiya zafi ce?

The particles ne / ce are copula/focus markers used mainly in equational or focus sentences, such as:

Wannan mota ce. – "This is a car."
Shi ne ya zo. – "It is he who came."

In Yau rana ta fi jiya zafi, you already have a full verbal predicate (ta fi jiya zafi), so you do not add ne/ce.
A sentence like *Yau rana ta fi jiya zafi ce is ungrammatical.

Can zafi here also mean “spicy”, or only “hot (weather)”?

zafi by itself can refer to any kind of heat: weather heat, the heat of an object, or the "hotness" (spiciness or temperature) of food or drink.

In Yau rana ta fi jiya zafi, because the subject is rana ("day") and the time words are yau / jiya, speakers automatically interpret zafi as "heat of the day / weather".

For food, you would usually make that explicit, for example:

Wannan miya ta fi ta jiya zafi. – "This soup is hotter than yesterday’s (in temperature or spiciness)."