westerly vs prevailing westerly

westerly and prevailing westerly both are nouns.

Word	Noun	Adjective	Verb	Adverb
westerly	Yes	Yes	No	Yes
prevailing westerly	Yes	No	No	No

As nouns, westerly and prevailing westerly are synonyms defined as:

westerly and prevailing westerly: the winds from the west that occur in the temperate zones of the Earth

westerly (noun)	prevailing westerly (noun)
the winds from the west that occur in the temperate zones of the Earth	the winds from the west that occur in the temperate zones of the Earth

westerly (adjective)	prevailing westerly (adjective)
of wind; from the west
moving toward the west

westerly (adverb)	prevailing westerly (adverb)
in a westward direction
from the west