Oh yes, and to answer Leenia's doubt; folk hereabouts do say "It's blowing southerly" meaning that it is coming from the south. It seems to me most unlikely that when wishing for a wind from the north they would reverse the usage and ask/instruct that the wind blow southerly.

Those wanting a northerly could say "blow southwardly" and be grammatically correct, but I haven't encountered such usage. I am involved in a maritime community just a few miles south of the Tyne, and while local dialects and traditions do vary, I doubt that they are so radically different as to reverse the meaning in this case.