strait of the northwest Pacific extending east from the Sea of Japan to the open ocean between the Japanese islands of Honshu (south) and Hokkaido. It is 15 to 25 miles (24 to 40 km) wide. The strait takes the Tsugaru Current, a warmer and saltier flow that is an extension of the Tsushima Drift, and carries it into the Pacific. Hakodate is a port city on Hokkaido; Aomori is its complement on Mutsu Bay, Honshu. The Seikan Tunnel linking Aomori and Hakodate cities runs beneath the strait.