southern vs southerly

southern is not a noun while southerly is a noun.

Word	Noun	Adjective	Verb	Adverb
southern	No	Yes	No	No
southerly	Yes	Yes	No	Yes

As adjectives, southern and southerly are synonyms defined as:

As adjectives, southern and southerly are synonyms defined as:

southern (noun)	southerly (noun)
	a wind from the south

southern (adjective)	southerly (adjective)
situated in or coming from regions of the south	from the south; used especially of wind
in or characteristic of a region of the United States south of (approximately) the Mason-Dixon line	situated in or oriented toward the south
from the south; used especially of wind
situated in or oriented toward the south

southern (adverb)	southerly (adverb)
	from the south
	toward the south