Ti presto il mio ombrello finché non smette di piovere.

Ti means to you.

In this sentence, it is an indirect object pronoun, and Italian usually puts these short pronouns before the conjugated verb:

• Ti presto = I lend to you / I’ll lend you

English often puts you after the verb, but Italian commonly uses a pronoun before it.

Compare:

• Presto il mio ombrello a Marco. = I lend my umbrella to Marco.
• Ti presto il mio ombrello. = I lend you my umbrella.

So ti is standing in for a te.

No. Here presto is a verb, not the adverb soon/early.

It comes from prestare = to lend.

So:

• io presto = I lend
• tu presti = you lend
• lui/lei presta = he/she lends

This is a very common point of confusion because Italian also has:

• presto = soon / early / quickly in some contexts

But in Ti presto il mio ombrello, it is definitely the verb prestare.

Italian often omits subject pronouns when they are already clear from the verb ending.

• presto already tells you the subject is io = I

So Ti presto il mio ombrello is perfectly natural.

You can add io for emphasis or contrast:

• Io ti presto il mio ombrello, ma lui no.
  = I’ll lend you my umbrella, but he won’t.

Without emphasis, Italian usually leaves io out.

In Italian, possessive adjectives usually take a definite article:

• il mio libro = my book
• la tua macchina = your car
• i nostri amici = our friends

So il mio ombrello is the normal pattern.

English does not use an article here, but Italian usually does.

A common exception is with many singular family members:

• mia madre = my mother
• tuo fratello = your brother

But ombrello is not in that exception group, so il mio ombrello is correct.

Here finché non means until.

The non in this structure is often called pleonastic or expletive non. It does not make the clause negative in the English sense.

So:

• finché non smette di piovere = until it stops raining

not

• until it doesn’t stop raining

This is a very common Italian pattern after words like finché when talking about something continuing up to the point when another event happens.

For an English speaker, the easiest way to understand it is:

• finché non = until

Sometimes yes, but finché non is very common and very natural here.

You may see both:

• finché non smette di piovere
• finché smette di piovere

In practice, for a learner, finché non is the safer pattern to recognize and use in sentences like this.

Just remember: in this structure, non usually does not create a real negative meaning.

Because smettere is normally followed by di + infinitive when it means to stop doing something.

So:

• smettere di fumare = to stop smoking
• smettere di parlare = to stop talking
• smettere di piovere = to stop raining

So the pattern is:

• smettere di + verb

not

• smettere a + verb

The subject is impersonal, like English it in it’s raining.

In Italian, piovere is usually used impersonally:

• Piove. = It’s raining.

So:

• smette di piovere literally means it stops raining

There is no real person or thing doing the action. Italian simply uses the third person singular.

Yes, it could be future, but the present tense is very natural in Italian for something happening now or in the immediate future.

So:

• Ti presto il mio ombrello... can mean I’ll lend you my umbrella... in a natural, conversational way.

A more explicitly future version would be:

• Ti presterò il mio ombrello finché non smetterà di piovere.

Both are grammatical, but the original sentence sounds very natural if someone is offering the umbrella right now.

Yes. That would also be correct.

• finché non smette di piovere
• fino a quando non smette di piovere

Both mean until it stops raining.

Finché is shorter and very common in everyday speech.
Fino a quando is a bit more explicit, but not dramatically different.

The sentence as given is the most natural order:

• Ti presto il mio ombrello finché non smette di piovere.

Italian word order is somewhat flexible, but the clitic pronoun ti normally stays before the verb:

• Ti presto il mio ombrello. = natural
• Presto ti il mio ombrello. = incorrect

You could move other parts for emphasis, for example:

• Il mio ombrello te lo presto finché non smette di piovere.

But that is a more marked structure. For a learner, the original order is the best model.

Because finché is stressed on the final vowel, and Italian marks that with an accent in words like this.

So it is written:

• finché

not

• finche

The accent helps show both the correct spelling and the correct stress.