New England weather is unpredictable, but more than likely you will have very pleasant cycling weather. Record highs are around 90 and record lows are around 30, but average highs are around 70 and lows around 50. Rain is always a possiblity, but Sept. is usually a pretty good month. If you check the forecast in the morning you should be able to make your decision then. You might also want to check a weather almanac site, such as Weather Underground - wunderground.com.

In case you don't know, the Memorial Bridge between Portsmouth NH and Kittery ME has been torn down and the replacement is scheduled to be opened in July 2013. The Sarah Long bridge (Rte. 1 Bypass) is closed to cyclists. The closest bridge open to cyclists is in Dover NH, which is a 28 mile detour if you are planning to ride from Kittery to Portsmouth.