The Roaring Forties are strong westerly winds that occur in the Southern Hemisphere, generally between the latitudes of 40° and 50° south.[2] The strong eastward air currents are caused by the combination of air being displaced from the Equator towards the South Pole, Earth's rotation, and the scarcity of landmasses to serve as windbreaks at those latitudes.
The Roaring Forties were a major aid to ships sailing the Brouwer Route from Europe to the East Indies or Australasia during the Age of Sail, and in modern times are favoured by yachtsmen on round-the-world voyages and competitions. The boundaries of the Roaring Forties are not consistent: The wind-stream shifts north or south depending on the season. The strong and continuous winds in the Roaring Forties make this zone advantageous for wind power in places such as New Zealand and Tasmania.[3]
Similar but even stronger conditions that occur at more southerly latitudes are called the Furious Fifties[4] and the Shrieking or Screaming Sixties.[5]