The Westerlies or the Prevailing Westerlies are the prevailing winds in the middle latitudes between 30 and 60 degrees latitude, blowing from the high pressure area in the horse latitudes towards the poles. These prevailing winds blow from the west to the east. The winds are predominantly from the southwest in the Northern Hemisphere and from the northwest in the Southern Hemisphere. Together with the trade winds, the westerlies enabled a round-trip trade route for early European sailing ships. Vessels returning to Europe from South and Central America, the West Indies, or the Southern Atlantic Seaboard of South America generally sailed North, turning Eastward at the Western Virginias to cross the Atlantic.
The westerlies can be particularly strong, especially in the southern hemisphere, where there is less land in the middle latitudes to cause friction and slow the winds down. The strongest westerly winds in the middle latitudes can come in the Roaring Forties, between 40 and 50 degrees latitude.
The Westerlies play an important role in carrying the warm, equatorial waters and winds to the western coasts of continents, especially in the southern hemisphere because of its vast oceanic expanse.
In the Southern hemisphere, because of the stormy and cloudy conditions, it's usual to refer to the Westerlies as the Roaring Forties, Furious Fifties and Shrieking Sixties according to the varying degrees of latitude.