A Black nor'easter is a persistent and potentially violent north-easterly storm that occurs on the east coast of Australia usually between late spring and early autumn, about two days a year (or more, depending on the intensity), although not a convection wind, but a storm system that develops offshore which can last several days. This is heralded by the rapid build-up of dense black cloud that can convert to a gale in well under one hour, and also bringing with it a heavy rainfall event usually accompanied by a thunderstorm. This type of storm was first recorded during the 1800s.