Hoje o céu está nublado, mas talvez fique ensolarado depois do almoço.

Because está is used for a temporary condition, while é is used for something more permanent or defining.

• O céu está nublado = The sky is cloudy right now / today.
• É nublado would sound more like it is cloudy by nature or it is a cloudy place/thing, which is not what you want here.

Weather conditions at a particular moment are normally expressed with estar:

• Está frio.
• Está chovendo.
• O dia está lindo.

So o céu está nublado is the natural choice.

Because talvez often triggers the subjunctive when the speaker is expressing uncertainty or possibility.

Here, talvez means maybe / perhaps, so the sentence is not stating a fact. It is saying something uncertain:

• talvez fique ensolarado = maybe it will become sunny

The form fique is the present subjunctive of ficar.

A very useful pattern is:

• Talvez + subjunctive

Examples:

• Talvez chova. = Maybe it will rain.
• Talvez ele venha. = Maybe he will come.
• Talvez fique ensolarado. = Maybe it will get sunny.

In everyday speech, you may sometimes hear talvez with the indicative, but for learners, talvez + subjunctive is the safest and most standard rule to follow in cases of uncertainty.

Here, fique means become or turn.

The verb ficar has several meanings in Portuguese, and that can be confusing. In this sentence:

• talvez fique ensolarado = maybe it will become sunny

So it is not really stay here. It is describing a change of condition.

Common meanings of ficar include:

• to stay: Vou ficar em casa. = I’m going to stay home.
• to become / get: Ficou feliz. = He became happy.
• to be located: Onde fica o banco? = Where is the bank?

In weather contexts, ficar often means to become:

• Vai ficar frio. = It’s going to get cold.
• O tempo ficou bom. = The weather became nice.

Both are possible, but ensolarado is a very common adjective meaning sunny.

So:

• ficar ensolarado = become sunny
• ficar com sol = more literally end up with sun / have sunshine

Both can work in weather talk, but ensolarado is often the more direct equivalent of English sunny.

Compare:

• Hoje está ensolarado. = Today it’s sunny.
• Hoje está com sol. = Today it’s sunny / there’s sun out.

Ensolarado sounds a bit more like a weather adjective, while com sol is also very natural and common in speech.

Do is a contraction of de + o.

• depois de = after
• o almoço = lunch
• depois de o almoço becomes depois do almoço

This kind of contraction is extremely common in Portuguese:

• de + o = do
• de + a = da
• em + o = no
• em + a = na

So:

• depois do almoço = after lunch
• literally: after the lunch

Even though English often says just after lunch, Portuguese normally uses the article here: depois do almoço.

In normal Portuguese, you need the article here: o céu.

• O céu está nublado. = natural
• Céu está nublado. = unnatural in standard usage

Portuguese uses definite articles more often than English does. When talking about the sky in general, you usually say o céu.

This happens with many nouns:

• O tempo está bom.
• O sol saiu.
• A chuva parou.

So for a learner, o céu is the form to use.

Yes, hoje can move, but putting it at the beginning is very natural because it sets the time right away.

The original sentence:

• Hoje o céu está nublado... = Today the sky is cloudy...

You could also say:

• O céu está nublado hoje...

Both are grammatically fine, but the emphasis changes slightly:

• Hoje o céu está nublado highlights today
• O céu está nublado hoje first presents the situation, then adds today

In everyday speech, Portuguese is fairly flexible with adverbs like hoje, but the sentence-initial position is very common.

Yes, but the meaning changes.

• Talvez fique ensolarado = Maybe it will become sunny
• Vai ficar ensolarado = It is going to become sunny

The first one expresses uncertainty. The second sounds much more confident, like a prediction.

So if you are not sure, talvez fique is better. If you think it definitely will happen, vai ficar is better.

Compare:

• Talvez chova mais tarde. = Maybe it will rain later.
• Vai chover mais tarde. = It’s going to rain later.

Not exactly.

• depois do almoço = after lunch
• à tarde = in the afternoon

These can overlap, but they are not identical.

Depois do almoço refers to a point in time relative to lunch.
À tarde refers to the afternoon in general.

Examples:

• Vou descansar depois do almoço. = I’m going to rest after lunch.
• Vou descansar à tarde. = I’m going to rest in the afternoon.

In your sentence, depois do almoço gives a more specific everyday time reference.

Céu is pronounced roughly like seh-oo, but as one syllable, not two fully separate ones.

A helpful approximation for English speakers is something like:

• SEH-ooh compressed into one syllable

Important points:

• The éu forms a diphthong.
• The stress is on céu itself, since it is only one syllable.
• The c before é sounds like s, so it is not keh-u.

A rough English-friendly guide:

• céu ≈ seh-oow said quickly

Also remember that céu means sky or heaven, depending on context.

Yes:

• Hoje = today
• o céu = the sky
• está = is
• nublado = cloudy
• mas = but
• talvez = maybe / perhaps
• fique = become / get / turn
• ensolarado = sunny
• depois do almoço = after lunch

So the structure is:

• Hoje — time marker
• o céu está nublado — main statement
• mas talvez fique ensolarado — possible change in weather
• depois do almoço — when that change may happen

A very literal reading would be:

• Today the sky is cloudy, but perhaps it becomes sunny after lunch

But in natural English, that becomes:

• Today the sky is cloudy, but maybe it’ll get sunny after lunch.

Actually, Portuguese can say both.

• Hoje está nublado. = Today it’s cloudy.
• Hoje o céu está nublado. = Today the sky is cloudy.

The version with o céu is a bit more explicit and descriptive. The version without it is very common too, especially in everyday speech and weather talk.

So:

• Está nublado. = very common, general weather statement
• O céu está nublado. = focuses more on the appearance of the sky

Both are correct; the sentence you have simply chooses the more descriptive version.

It can describe both the sky and the weather in general.

You can say:

• O céu está nublado. = The sky is cloudy.
• Hoje está nublado. = It’s cloudy today.
• O tempo está nublado. = The weather is cloudy / overcast.

In practice, nublado is often used generally for weather conditions, not just the visible sky. It is one of the most common weather adjectives in Portuguese.