Definitions for "Roaring forties"
The middle latitudes of the southern hemisphere. So called from the boisterous and prevailing westerly winds, which are especially strong in the South Indian Ocean up to 50° S.
A nautical expression for the region of westerly winds in south temperate latitudes, which reach their greatest development south of 40°S. A general term for the prevailing westerly winds in the temperate latitudes of both hemispheres is Brave West Winds.
The area between 40 degrees and 50 degrees latitude noted for strong winds and large seas.