Sailors call the Roaring Forties between 40 and 50 degrees south of the equator.
During the Age of Sailing (circa 15th to 19th century), these strong prevailing winds propelled ships across the Pacific, often at breakneck speed. However, sailing to the west in heavy seas and strong headwinds could take weeks, especially around Cape Horn in the southern tip of South America, making it one of the most dangerous navigational steps in the world.
The roaring forties take shape as the warm air near the equator rises and moves toward the poles. The hot air moving toward the poles (on both sides of the equator) is the result of nature trying to reduce the temperature difference between the equator and the poles created by the uneven heating of the sun.
This process establishes global circulation cells, which are mainly responsible for wind patterns on a global scale. The air descends to the surface of the Earth at about 30 degrees north and south of the equator. This is known as subtropical high pressure crest, also known as the latitudes of horses. Here, as the temperature gradient decreases, air is diverted to the poles by the rotation of the Earth, causing strong west winds and prevailing at about 40 degrees. These winds are the roaring forties.
The Roaring Forties in the Northern Hemisphere do not have the same blow they have in the Southern Hemisphere. This is because the large land masses of North America, Europe and Asia obstruct the air flow, while in the southern hemisphere, there is less land to break the wind in South America, Australia and New Zealand.
While the Roaring Forties can be ferocious, 10 degrees south are even stronger gale force winds called Furious Fifties. And at 10 degrees south of the furious fifties lies the Screaming Sixties! We can thank the intrepid sailors of yesteryear for these tremendously descriptive terms.