Storm Dennis will bring a month of rainfall for some parts of the UK in just 24 hours this weekend, the Met Office has said.
It has issued amber warnings for rain, starting at 3pm on Saturday and running for 24 hours. There are also less serious yellow warnings for both wind and rain.
The whole country apart from Northern Ireland and northern Scotland will be hit on Saturday, while every part of the UK will be affected on Sunday.
It is feared that properties could be flooded or even cut off – partly because Storm Ciara has already saturated the ground.
Dennis may bring wind speeds – especially in coastal regions – of up to 70mph.
Worst-affected areas will see more than 100mm of rain in one day, while between 40-80mm is likely in other parts of the UK.
“Even in London and parts of the South East there could be three quarters of a month’s rainfall,” Tom Morgan from the Met Office told Sky News.
Power supplies could be damaged and public transport delayed or cancelled. Coastal areas are likely to be battered by huge waves.
Storm Dennis will sweep in on Saturday morning bringing warm and moist air, Mr Morgan said.
While it will be a “notch down from last weekend”, when Storm Ciara brought winds of up to 97mph, he described Dennis as a “very potent deep area of low pressure”.
Given its name by the Met Office, Dennis is developing in the North Atlantic before tracking eastwards towards the UK and Ireland.