"I don't like southern weather."
Is says I need to say "the" southern weather. I am a native English speaker and I do not need that.
Said no one, ever
Well it's just Duo being picky: first he wasn't used to the weather here (wherever this here was), then the weather in the north was too cold, and now he plain doesn't like the weather in the south :)
Why is "up north" acceptable and "down south" not? So not to hurt the feelings of 澳大利亚人？
It is common practice to not require a "the" in front of "weather". But it is required in this answer.
Why do we need 'the' before 'south'?
"The south" is a place (and therefore a noun). "South" is an adjective.