The Seaport in August is hot and busy. The Seaport in late September is one of the nicest places to spend an afternoon in New York, and it's a five-minute walk from our door.
Here's what changes. The harbor breeze that feels thin in summer turns into the main event once the temperature drops into the sixties. The tourist crush eases off after Labor Day. The Rooftop at Pier 17 runs its last stretch of outdoor concerts through September and October, so on the right night you can hear a show from the esplanade whether or not you have a ticket. And the light gets better: low sun coming down the East River, the Brooklyn Bridge lit from the side, the whole thing over in about twenty minutes and worth being outside for.
A bit of orientation, because the Seaport confuses people. Fulton Street runs east from Broadway and hits the water at the piers. Pier 16 is where the South Street Seaport Museum keeps its historic ships. Pier 17 is the big modern building with the rooftop venue on top. Pier 15 just south has the two-level esplanade with the lawn and the deck chairs. The cobblestone blocks around Front Street and Peck Slip are the old part, and they're the prettiest streets in Lower Manhattan in October.
Go on a weekday afternoon if you can. Weekends here are livelier than the rest of the Financial District, which is a plus if you want company and a minus if you want the piers to yourself.
Below is how we'd spend a fall afternoon down there, in order.