Keelung, officially known as Keelung City, is a major port city situated in the northeastern part of Taiwan. It borders New Taipei with which it forms the Taipei–Keelung metropolitan area, along with Taipei itself. Nicknamed the Rainy Port for its frequent rain and maritime role, the city is Taiwan's second largest seaport. Keelung City is located in the northern part of Taiwan Island. It occupies an area of 132.76 km2 and is separated from its neighboring county by mountains in the east, west and south. The northern part of the city faces the ocean and is a great deep water harbor since early times. Keelung has a humid subtropical climate with a yearly rainfall average upwards of 3,700 millimetres. It has long been noted as one of the wettest and gloomiest cities in the world; the effect is related to the Kuroshio Current.Although it is one of the coolest cities of Taiwan, winters are still short and warm, whilst summers are long, relatively dry and hot, temperatures can peek above 26°C during a warm winter day, while it can dip below 27 °C during a rainy summer day, much like the rest of northern Taiwan. However its location on northern mountain slopes means that due to orographic lift, rainfall is heavier during fall and winter, the latter during which a northeasterly flow prevails. During summer, southwesterly winds dominate and thus there is a slight rain shadow effect. Fog is most serious during winter and spring, when relative humidity levels are also highest.