A powerful, rare weather feature could make Eunice the most dangerous storm to hit Britain in recent times, forecasters have warned.
Eunice, due to hit on Friday, could bring in a "sting jet", which is a small area of extremely intense wind that can form inside storms.
Although they are rare, there is a possibility one could hit the UK when Storm Eunice arrives in the early hours of Friday morning.
The red warning is for the south-west where 145kph winds are expected to hit the coastline, and gusts of up to 160kph threaten large parts of southern England.
Storm Dudley left thousands without power in northern England and Scotland on Wednesday.
The Meteorological Office on Thursday issued amber warnings for most of England, and then upgraded Devon, Cornwall and parts of south Wales to the red warning.
What is a sting jet?
A sting jet is a small area of extremely intense wind that can form inside storms passing over the UK, Ireland and parts of north and central Europe.
Compared to the size of the storm they are very narrow, usually about 48 kilometres across, and tend to last only three or four hours.
They were only formally recognised when one occurred in the Great Storm of October 1987, when wind speeds reached 185kph and millions of trees were brought down.
How are sting jets are formed?
Non-tropical storms are caused by areas of low pressure that create weather fronts.
These fronts separate into areas of cold and warm air, and the way they interact with one another is what causes bad weather.
Focused streams of air called conveyor belts form ahead of the two fronts.
The cold conveyor belt, which is a strong stream of cold air, pulls down into the storm before the warm conveyor belt, also known as a dry intrusion.
Cold conveyors bring snow and rain, which evaporate and speed up the stream of cold air falling into the storm.
This is known as a sting jet — the "sting in the tail" of the storm.
But the biggest sign of a sting jet is high winds.
After the storm starts to develop they can also be seen on satellite images as the end of the cold conveyor belt forms a hook-shaped cloud that looks like the sting of a scorpion's tail.
Will Storm Eunice cause a sting jet?
The prediction of "extremely strong winds" when Eunice hits the UK on Friday suggests they might be fast enough to result in a sting jet.
But even if the rare weather event does not happen, the winds caused by Eunice could be extremely damaging.
The strongest winds are forecast for southern England but there could also be 145kph gusts in south-west England and south Wales. Wind warnings are also in place for northern England and Scotland.
"It is the most powerful storm we have seen in recent years and we should tie down anything loose," the Met Office's Aidan McGivern said.
