What extreme weather conditions or natural disasters have happened in New York's history?
There were a number of blizzards, probably the worst was the Great Blizzard of March 11 to March 14, 1888. It produced up to 50 inches of snow, and drifts of up to 50 feet. Another particularly bad one was in 1947.
There were vary bad heat waves in New York in 1883 and August 9-15, 1986.
The history of New York has also seen a number of other disasters. See the related link.
Pretoria has had no significant natural disasters in recent history. Isolated incidents such as burning buildings and flash floods in the surrounding rural areas have happend, but resulted in minimal loss of life. Although not "natural" disasters, road accidents and violent crime are much greater risks in the greater South African region.