Kite season in NY begins the day after Labor Day. Lasts until Memorial Day... It's tough to find enough open space to fly during the summer, not to mention too hot.
There used to be more festivals around the NYC area, I can only find one on the AKA calendar this year.
The Coney Island festival isn't listed on the official AKA calendar, but looks like it's at the end of September.
Another one not on the AKA calendar...
And the only official event announced so far on Long Island is...
But, every Sunday people fly at Jones Beach, just east of field 6.
Festivals are a great way to get out, fly, and meet other people who like to fly.