The British Army is on standby and people are being urged to stay at home as the UK braces to be battered by Storm Eunice.
A rare red weather warning – the highest alert, meaning a big impact is very likely – has been issued by the Met Office for parts of Cornwall, Devon, Somerset and South Wales.
The warning has been issued for between 07:00 and 12:00 on Friday due to the combination of high tides, strong winds and storm surge.
The Met Office said there is a risk of "flying debris resulting in danger to life" and "damage to buildings and homes, with roofs blown off and power lines brought down".
During a visit to RAF Waddington in Lincolnshire, the Prime Minister said "of course" the Army was on standby to help those affected by Storm Eunice.
Boris Johnson added that the Government is also "offering all the support that we can" to those impacted by Storm Dudley on Wednesday.
Amber warnings, the second-highest alert level, for wind are in place across the whole of England for Storm Eunice from 05:00 to 21:00 on Friday.
While yellow weather warnings, the next level down, for wind and snow are in force for a large part of Scotland – where blizzards are predicted – and the whole of Northern Ireland.
North Cornwall, North Devon and Sharpness in Gloucestershire are feared to be the worst-hit areas due to the tidal impact from the surge and very high spring tides.
There could be winds of more than 90mph in the South West, while further inland gusts of up to 80mph are forecasted.