The South Equatorial Current, flowing west along the equator, swings southward east of New Guinea, turns east at about 50 deg south latitude, and joins the main westerly circulation of the Southern Pacific, which includes the Earth-circling Antarctic Circumpolar Current. Mid-latitude westerly air streams occur in both northerly and southerly latitudes, bringing marked seasonal differences in temperature. The monsoon region lies in the far western Pacific between Japan and Australia. Characteristic of this climatic region are winds that blow from the continental interior to the ocean in winter and in the opposite direction in summer. Consequently, a marked seasonality of cloudiness and rainfall occurs.
Typhoons often cause extensive damage in the west and southwest Pacific.
The greatest typhoon frequency exists within the triangle from southern Japan to the central Philippines to eastern Micronesia. Although more poorly defined than the other climatic regions, two major doldrum areas lie within the ocean, one located off the western shores of Central America and the other within the equatorial waters of the western Pacific. Both areas are noted for their high humidity, considerable cloudiness, light fluctuating winds, and frequent calms. The Andesite Line is the most significant regional distinction in the Pacific. It separates the deeper, basic igneous rock of the Central Pacific Basin from the partially submerged continental areas of acidic igneous rock on its margins.