I'm just north of Trip in NH. I have noticed that the weather generally 'turns' about the 3rd week of October here. For the first couple weeks in October, you might enjoy an Indian Summer, but by about the 20th or so, you'll experience more wind, and the 'very brisk' fall weather. The nights tend to be in the 30s at this time of the month with daytime temps in the low-mid 40s.
Definitely bring your warmer clothes...wool is very comfy choice. Halloween could be rainy & quite cold- seems like 8 out of 10 Trick-or-Treat years we have cold rain.
Here's a cool pic stolen from the web on the average monthly temps (keeping in mind that the first two weeks tend to be quite different than the last two, generally):