On Thursday at 550 Vanderbilt, the Greenland Forest City 2017 Mid-Autumn Festival (to sell condos)

Maybe it'll be a local tradition too? On Thursday, October, 5, Greenland Forest City Partners will hold its Greenland Forest City 2017 Mid-Autumn Festival:

In observing the Chinese traditional Mid-Autumn Festival, Greenland Forest City Partners would like to invite you to join us, along with our exclusive sales broker, Ryan Serhant Team, in celebrating the Chinese holiday at our proud condominium at 550 Vanderbilt Avenue, Brooklyn. There will be hors d’oeuvres, raffle prizes and more!

Given that they're not holding the festival at, say, the affordable 535 Carlton, and the presence of the "exclusive sales broker," I'd have to guess this has to do with selling condos. It's a traditional harvest festival and a public holiday in China, Taiwan, and Hong Kong.