Nagasaki and Nishisonogi Peninsulas are located within the city limits. The city is surrounded by the cities of Isahaya and Saikai, and the towns of Togitsu and Nagayo in Nishisonogi District.
Nagasaki lies at the head of a long bay which forms the best natural harbor on the island of Ky?sh?. The main commercial and residential area of the city lies on a small plain near the end of the bay. Two rivers divided by a mountain spur form the two main valleys in which the city lies. The heavily built-up area of the city is confined by the terrain to less than 4 square miles (10 km).
Nagasaki has the typical humid subtropical climate of Ky?sh? and Honsh?. Apart from Kanazawa and Shizuoka it is the wettest sizeable city in Japan and indeed all of temperate Eurasia, and in the summer the heat and humidity can be very unpleasant, with wet bulb temperatures sometimes reaching 26 °C (79 °F). In the winter, however, it is drier and sunnier than Got? to the west, and temperatures are slightly milder than further inland in Ky?sh?. Since records began in 1878 the wettest month has been July 1982 with 1,178 millimetres (46 in) including 555 millimetres (21.9 in) in a single day, whilst the driest month has been September 1967 with 1.8 millimetres (0.07 in)