Moncton has a long winter (snow on the ground from December into April) and a brief, intense summer. The best time to visit is from June to early October. July and August are warm and often humid; September is crisper, with autumn colour starting late in the month.
If the tidal bore is part of your trip, check a tide chart and time your visit for one of the higher tides — the bore varies in size considerably from day to day. The Festival acadien is held in early August and is a good reason to time a visit if you are interested in the Acadian musical and cultural tradition.