Learn Portuguese (Portugal): O vento é forte.

Está vento is an expression that describes the general weather condition ("it's windy"). In this sentence, the wind itself is the main subject (O vento). We are talking about "the wind" as a specific thing, so we describe it with the verb "to be" (é) and an adjective (forte).

Why use é (permanent) instead of está (temporary) if the wind might stop blowing later?

Using é describes the core characteristic of the specific wind you are experiencing (e.g., this particular wind is a strong one). However, if you want to emphasize that the wind is unusually strong today compared to normal, you can absolutely say O vento está forte. Both are correct depending on what you want to emphasize!

Vento is a masculine word. Why doesn't the adjective forte end in an "o"?

Adjectives that end in -e in Portuguese are usually gender-neutral. They keep the exact same form whether the noun is masculine or feminine. Because of this rule, you have o vento forte (the strong wind - masculine) and a chuva forte (the heavy rain - feminine).

How should I pronounce the word O at the beginning of the sentence?

When the letter o stands alone as the definite article meaning "the", it is pronounced like a short "oo" sound (similar to the vowel sound in the English word "boot"), not like the English letter "O".