Intertropical Convergence Zone

The NE trade winds are bound to the south by the ITCZ, which remains north of the equator throughout the year east of meridian 160 °W. To the west of that longitude it moves south of the equator during the northern winter, from about December to April or early May. During the summer of the northern hemisphere, when the SE trade winds are at their strongest in the South Pacific, the ITCZ disappears altogether west of about 150°W, where the two trade wind systems almost run into each other and the belt of doldrums is virtually nonexistent. In the western part of the North Pacific, the ITCZ is only present during the changeover periods of the monsoons, either from mid-April to mid-May or from mid-September to mid-November.

The weather inside the zone is typical doldrums weather, with calms or very light winds alternating with squalls, heavy rain, and thunderstorms. However, as one moves west, the frequency of calms and light variable winds becomes less and the prevailing winds, even inside the doldrums, are easterlies. This is a fact worth bearing in mind if planning transequatorial passages especially west of the meridian of the Marquesas.

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