To be more accurate , the second sentence is correct as it is . I mean south here is correct ,not wrong . Southerly is also correct as it ican be used as an adjective or an adverb and as they are(south and southern) often interchangeable. Southern is also correct .Read this carefully , please
South and southern are used to talk about places that are relatively closer to the South Pole. Southern is an adjective, meaning in or from the south of a country or area. Because it is an adjective, it needs a noun with it.
Aswan is in southern Egypt. NOT Aswan is in (the) southern.
In England, the southern dialects are more prestigious.
South can be used as a noun, adjective (in or facing the south), or adverb (towards the south).
noun:
Aswan is in the south of Egypt.
My mother comes from the south. (context would tell us what country is meant)
Adjective:
The city is on the south coast.
A south wind is blowing today. (blowing from the south)
Adverb:
We drove south for three hours.
Southerly can be used as an adjective or adverb and refers to orientation—the way something is facing or moving. Again, a southerly wind or current is coming from the south, but a southerly side of a house faces the south.
Adjective:
The southerly side of our house gets a lot of sun even in winter.
They walked in a southerly direction.
Adverb:
They got in the car and took off southerly.
South and southerly can be interchanged when they mean facing the south or going towards the south, but I suspect that south is more common than southerly — at least where I come from.
We have a garden on the southerly/south side of the house.
We walked south/southerly
Best Regards.