Are you coming to
NYC as a tourist, do you live in NYC, or are you passing though?
I ask because that can make a difference. If you are a tourist, August in NYC is not pleasant weather wise. It is hot and steamy and later September is much, much nicer. In August, especially this year, the heat radiates off the sidewalks. A person is in a pub or restaurant and they look outside, see that the sun has set, and subconsciously they think it will be nicer out. Then they walk outside.
Another issue is the increase in crime. While we are still safer than many cities, it is on the rise and continuing to increase. It is also much more random than a decade ago. In October, the creatures tend to crawl back under their rocks, so it is a little safer.
If you are a tourist and going back to South Carolina, October is not a bad month, I am often out on the
water well into December although it is chillier than in October or often mid November. . If you are returning in the September to November time frame, there are plenty of places to duck into on the way down, at least until Virginia Beach, and you can take the Chesapeake-Deleware
Canal to the bay. After that you have to go outside again. The weather windows do get smaller later in the year, but it is doable.
Once you get to NYC, where will you tie up, and how long are you staying?
Good luck with your trip.