A situação parece horrível.

Here, A is the feminine singular definite article, so it means the.

• a situação = the situation
• uma situação = a situation

This is a very common point for English speakers, because Portuguese a does not mean a/an in this sentence. The indefinite article would be uma.

In Portuguese, every noun has a grammatical gender, usually masculine or feminine. Situação is a feminine noun, so it takes the feminine article a.

A useful pattern:

• Nouns ending in -ção are very often feminine.
• So you get things like:
  • a situação
  • a informação
  • a decisão

This gender is a grammar feature, not necessarily something logical about the object or idea itself.

Parece is the third-person singular present tense of parecer, which means to seem or to appear.

So:

• A situação parece horrível = The situation seems horrible

It suggests an impression or appearance, not an absolute statement. That is slightly different from saying the situation is horrible.

Because the subject is singular:

• a situação = singular
• therefore the verb is singular: parece

If the subject were plural, the verb would also be plural:

• As situações parecem horríveis = The situations seem horrible

This is basic subject-verb agreement.

Because horrível is not directly describing the noun inside the noun phrase. It is being used as a predicate adjective after the verb parece.

Compare:

• a situação horrível = the horrible situation
  Here, horrível directly modifies situação.

• a situação parece horrível = the situation seems horrible
  Here, horrível describes how the situation seems.

So the structure is:

• subject
  • verb
    • predicate adjective

Some Portuguese adjectives have the same form for masculine and feminine in the singular. Horrível is one of them.

So you get:

• o problema horrível
• a situação horrível

No change in the singular.

What does change is the plural:

• horrível → horríveis

Examples:

• a situação horrível
• as situações horríveis

Yes, but the meaning changes slightly.

• A situação parece horrível = the situation seems horrible
• A situação está horrível = the situation is horrible right now / is in a horrible state
• A situação é horrível = the situation is horrible, more like a general statement or judgment

So parece is softer and less direct. It leaves room for uncertainty or appearance.

Normally, no. That sounds unnatural in standard Portuguese.

A singular count noun like situação usually needs a determiner:

• A situação parece horrível
• Essa situação parece horrível
• Uma situação parece horrível

Leaving out the article would usually not work in an ordinary sentence like this.

They help show pronunciation.

In situação:

• ç sounds like s
• ã is a nasal vowel
• ão is a very common nasal ending in Portuguese

In horrível:

• the accent in í shows the stressed syllable: rí
• so the stress is on rí, not on the last syllable

These marks are important and are part of the correct spelling.

A rough English-style approximation is:

ah see-too-ah-SOWN pah-REH-see oh-HEE-veew

That said, some sounds do not match English exactly, especially:

• the nasal sound in -ão
• the Portuguese r
• the final sound in horrível

A more useful breakdown is:

• A situação → stress near the end: -ção
• parece → stress on re
• horrível → stress on rí

It would be:

As situações parecem horríveis.

Notice all the changes:

• A → As
• situação → situações
• parece → parecem
• horrível → horríveis

So Portuguese shows agreement in several places when you switch from singular to plural.