It has caused big problems for people living in parts of northern England and Scotland.
Heavy rain and high-speed winds have resulted in water flooding roads and houses.
Hundreds of people have been forced to leave their homes as rivers burst their banks and flood waters rose quickly.
Around one month's worth of rainfall fell in just 24 hours.
There are more than 50 flood warnings in place across the UK and the Met Office has advised people not to travel.
Dozens of trains have been cancelled, and roads have been closed in Scotland, England and Wales.
Schools and hospital services have been closed in parts of northern England, as emergency services continue to battle against the effects of Storm Desmond.