<P> In meteorology, the trade winds act as the steering flow for tropical storms that form over the Atlantic, Pacific, and southern Indian Oceans and make landfall in North America, Southeast Asia, and Madagascar and eastern Africa, respectively . Trade winds also transport African dust westward across the Atlantic Ocean into the Caribbean Sea, as well as portions of southeastern North America . Shallow cumulus clouds are seen within trade wind regimes, and are capped from becoming taller by a trade wind inversion, which is caused by descending air aloft from within the subtropical ridge . The weaker the trade winds become, the more rainfall can be expected in the neighboring landmasses . </P> <P> The term trade winds originally derives from the early fourteenth century late Middle English word' trade,' meaning "path" or "track ." The Portuguese recognized the importance of the trade winds (then the Volta do mar, meaning in Portuguese "turn of the sea" but also "return from the sea") in navigation in both the north and south Atlantic ocean as early as the 15th century . From West Africa, the Portuguese had to sail away from continental Africa, that is, to west and northwest . They could then turn northeast, to the area around the Azores islands, and finally east to mainland Europe . They also learned that to reach South Africa, they needed to go far out in the ocean, head for Brazil, and around 30 ° S go east again . Following the African coast southbound means upwind in the Southern hemisphere . In the Pacific ocean, the full wind circulation, which included both the trade wind easterlies and higher - latitude Westerlies, was unknown to Europeans until Andres de Urdaneta's voyage in 1565 . </P> <P> The captain of a sailing ship seeks a course along which the winds can be expected to blow in the direction of travel . During the Age of Sail, the pattern of prevailing winds made various points of the globe easy or difficult to access, and therefore had a direct effect on European empire - building and thus on modern political geography . For example, Manila galleons could not sail into the wind at all . </P> <P> By the 18th century the importance of the trade winds to England's merchant fleet for crossing the Atlantic Ocean had led both the general public and etymologists to identify the name with a later meaning of' trade', "(foreign) commerce". Between 1847 and 1849, Matthew Fontaine Maury collected enough information to create wind and current charts for the world's oceans . </P>

Why are the winds north easterlies in the tropics