It's hot today, isn't it?

There is nothing wrong with sentence grammar, but it is illogical.

In English, we say the weather is good/good/bad, and so on.

(The weather is good, not good, ...)

Generally don't say "hot weather".

But you can say it's hot today.

As for the new concept sentences,

"It is often cold in the north and windy in the east."

The first sentence should read as follows

"It is often cold in the north and windy in the east."

Comparative logic

The second sentence

"Our climate is not very good, but it must be interesting."

There is nothing wrong with it.

I am Canadian, and English is my first language.