Notus

Notus is the South Wind, one of the four Anemoi. As his brother, Boreas the North Wind resides in Quebec (the oldest Northern American settlement), Notus may reside in one of the older Southern American settlements.

Notus' winds are heavy and moisture filled, creating fog and mists.

The Last Olympian
Although Notus in particular was never mentioned, Hermes said that Aeolus sent the wind gods to defend Olympus from the air. It is presumed that Notus was among them.

The Lost Hero
In The Lost Hero, he is mentioned by an angry Boreas, since apparantly Notus gets to take spring break in Cancun. At the end of the book, when the demigods were trying to decide when to leave for Greece, Chiron advised them to leave during the summer since Notus's winds are the most gentle.

Trivia

 * It's possible that he has demigod children (although none are mentioned in the series), since when the Boreads were questioning Leo about his fire powers, they thought that he may have been 'a child of the South WInd', sent to spy on them. This also implies that, while Boreas is associated with ice and snow, Notus is probably associated with heat and fire.