Orange warnings for the rain are in place for 24 hours from Saturday afternoon in the North West and South of England and South Wales.
The storm "is expected to intensify" and could bring one month of precipitation in one day. the Met Office says such heavy rain poses a greater risk of widespread flooding - a life threatening hazard - than storm Ciara caused the weekend before.
At the same time, delays and cancellations of transportation services are expected, Rail network warning that runways in the northwest may be particularly at risk due to waterlogging since last week.
Jake Kelly, the director of passengers for Network Rail, said that Storm Ciara had interrupted services after "pouring a month and a half of rain on us".
He said Saturday and Sunday "we are preparing for the same thing".
Driving conditions are also expected to be affected as rain will "significantly reduce visibility," said AA patrol of the year, Ben Sheridan.
He added, "For those braving the storm, drivers need to make sure they consider the conditions. Slow down, allow longer stopping distances and watch out for potential dangers. "
There will be an increased increased risk of flooding in parts of West and North Yorkshire, Lancashire and Great Manchester, Hampshire, Sussex, Surrey and Kent, according to the Environment Agency.
He issued 16 flood warnings in England and 109 other less serious warnings.
The hardest hit areas will see more than 100mm of rain in one day, while between 40 and 80mm (1.7 to 3.1 inches) 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 of rain," Tom Morgan of the Met Office told Sky News.
Environment Agency flood officer Caroline Douglas said her crews are preparing for the storm but advised people to watch the alerts online and warned of any attempts to drive or drive cross the flood waters.
She said: "We will continue to closely monitor the weather and level of the rivers and we are preparing to issue flood warnings to communities at risk to help them act and stay safe. "
Yellow wind and rain warnings are also in place for the whole of England and the south of Scotland on Saturday, which will spread to the whole of the United Kingdom by Sunday.
Wind gusts of up to 70 mph can be expected - especially in coastal areas.
Alex Deakin of the Met Office said the wind should not be as strong as that of Storm Ciara, but that it was still likely to cause "disturbance".
Most weather warnings will be gone by Monday. However, the whole of Scotland will remain under a yellow wind warning until noon.