The waters that surround the Saint John area, specifically in the Bay of Fundy and harbour Saint John, never freeze in the winter. The weather, however, can get very cold during the winter months. January is definitely the coldest month of the year, which makes it the least popular month for tourists.
July and August are the warmest months in Saint John , and the warmest time of the day is early afternoon; in the evening as the sun drops the wind will shift from off shore to onshore and lends to having cool evenings and some dew on most days. The Bay of Fundy is the world's best natural air conditioning unit and provides cooling breezes at night and little need for air conditioning near the bay.
The summer months, including July, in Saint John can be very pleasant with an average temperature of about 20°C (70°F). However, the area has been known to receive cold air during the summer which can make the temperatures drop. Fog is not uncommon; after all, the fog horn was invented in Saint John in 1810.
Spring to fall are the most popular times for visitors to Saint John. The weather can be either warm or cool, but always pleasant. September is a grand month, usually dry unless the tail end of a tropical storm reaches this far (rare). The fall colors are at the peak from the end of September to the first week of October, depending on the summer conditions, and is difficult to predict accurately.