Michael White's Altamarea Group has been working in the old Park Avenue Winter/Spring/Summer/Fall space for quite a while now on a secret project. Whatever that project turns out to be, it will make its debut sometime this fall, say a rep. There are a couple of job postings on Craigslist for high level positions like sommelier and assistant general manager. The team is looking for people with fine dining experience, so it's likely this place won't be something ultra causal like White's pizza spot Nicoletta.
Update: Eater hears a rumor that the restaurant will be French and fancy.