Gusts of up to 80 mph (120 kph) are predicted in the South West , moving north and eastwards overnight.
There are fears about falling trees, buildings being damaged, flooding, travel disruption and power supplies.
The Met Office said 20-40mm (0.80-1.6 ins) of rain might fall within six to nine hours in the wettest areas.
It said the predicted storm - named St Jude after the patron saint of depression and lost causes, whose feast day is Monday - was not one "you would see every year".
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