O vento norte é frio no inverno.

In Portuguese we almost always use a definite article before a noun, even when making general statements.
• O is the masculine singular article “the.”
• English often drops “the” with general nouns (“North wind is cold…”), but Portuguese keeps it.

Here norte functions like an adjective meaning “north,” so no preposition is needed.
• vento norte = “north wind.”
• You can also say vento do norte, literally “wind of the north,” and it’s common in everyday speech. Meteorological reports often use the shorter vento norte.

no is a contraction of the preposition em (“in”) + the article o (“the”).
• em + o inverno → no inverno = “in the winter.”

All season names in Portuguese are masculine nouns: o inverno, o verão, o outono, o inverno.
They normally appear with the definite article, especially in time-expressions like no inverno, no verão.

This is a predicate adjective construction:
• vento norte (subject) + é (copula “is”) + frio (adjective).
In Portuguese, adjectives that follow ser/estar almost always come after the verb. If you wrote vento frio, you’d be attributing “cold” directly to “wind” in a noun phrase.

Yes. You’d say:
• Os ventos norte são frios no inverno.
or, more literally,
• Os ventos do norte são frios no inverno.
Here os is the plural article, ventos is the plural of vento, and são is “are.”

A reasonable phonetic approximation is:
[ˈvẽ.tu ˈnɔɾ.tɨ ɛ ˈfɾi.u nu ĩˈvɛɾ.nu]
• “vẽ” has a nasal ẽ,
• final o often sounds like [u],
• word-internal r is a tapped [ɾ],
• final e in norte is [ɨ].essions