Have you noticed how the tropical storms along the equator move from east to west? But as they move north, they head from west to east? This is because there are bands of prevailing winds which vary the latitude. The famous trade winds are winds from the east that can be found near the equator. As you move north of 30 degrees, you move into prevailing westerlies. Between these two areas, would be fairly calm winds. Sailing ships that moved out of the prevailing winds would be bogged down, running out of water and supplies. Horses meant for the New World, would be thrown overboard -- giving the name “horse latitudes” to the region.
Mary Knapp, Weather Data Library