A strong cyclone devastated the city of Algiers on 9-10 November, 2001. Over 250mm of rain fell in a 12-hour period early that Saturday accompanied by near hurricane force winds. The heavy rains led to massive flooding killing 737 people in Algeria and leaving 23,000 homeless. This amounted to the worst flooding and second worst natural disaster to hit Algeria since independence in 1962. A high-resolution numerical simulation of the storm suggested that the cyclone was spawned by when a filament of potential vorticity shed from an intense tropopause fold that balled up into an intense local vortex just north of the city. A particularly interesting facet of the simulated storm evolution was the decent of an upper level potential vorticity filament the lower troposphere around 700 hPA. It is shown that the decent may have been connected to the existence of very warm Saharan air drawn northward from the south. The high temperature and low stability of that air apparently allowed the vortex descend to the surface and stretch vertically causing it to give rise to strong cyclonic surface winds. The associated Ekman pumping of moisture into the base of the vortex created the observed slantwise lifting that gave rise to catastrophic flooding rains. This storm genesis process is reminiscent of what appears to happen in association with polar low formation in the north Atlantic where the Saharan coast is replaced by the southern boundary of the polar pack ice and warm Gulf Stream waters to the south..