Portsmouth, located in southeastern New Hampshire in Rockingham County, is equidistant from Portland, Maine, to the north and Boston, Massachusetts, to the south. About three miles inland from the Atlantic Ocean, Portsmouth is at the mouth of a broad tidal basin for six inland rivers. Portsmouth itself lies on the banks of the Piscataqua River. On the opposite bank of the Piscataqua is the city of Kittery, Maine site of the Portsmouth Naval Shipyard. The only seaport in the state, Portsmouth has one of the deepest harbors in the world. The land around the harbor is hilly, sloping down to Piscataqua Bay.
Portsmouth's winters are relatively mild and wet because of the mitigating influence of the Atlantic Ocean; average snowfall during the winter is 62 inches. Summer, which can be warm and humid, is sometimes lightened by ocean breezes. The traditional New England storms off the Atlantic, known locally as "northeasters," are mostly spent by the time they reach Portsmouth.
Area: 15.7 square miles (2000)
Elevation: 20 feet above sea level
Average Temperatures: January, 19.9° F; July, 69.5° F; annual average, 44.7° F
Average Annual Precipitation: 46 inches of rain; 62 inches of snow