What are the "roaring forties"?

Some of you Europeans have maybe not heard of the "Roaring Forties", name given to the latitudes between 40°S and 50°S, so called because of the strong and prevailing westerly winds. Because there is less landmass to slow them down, the winds are especially strong in the Southern Hemisphere, notably in the South Indian Ocean.

Cook Strait is the waterway between the North and South Islands of New Zealand. It's located at about 41 degrees south and is the conduit between the Tasman Sea and the Pacific Ocean. As you can imagine the currents through it are huge, and the waves regularly get higher than 10 metres.