Residents in a large part of UK have been advised to prepare and brace for flash flooding and major traffic disruptions in the next 48 hours.
"There may be some flooding of low-lying land and roads, some disruption to travel and possibly flooding to individual properties," the Environment Agency said.
The Met Office said persistent heavy rains up to 70mm will fall and flood Lincolnshire, South Yorkshire and the Humber. A yellow "be aware" warning has been issued across the East of England.
Weather experts said pretty much the whole of Great Britain will see rain at some point over the next 48 hours.
South East, Midlands and East Anglia were likewise given flood alerts due to potential surface water and low-lying rivers. These areas include High Wycombe, Newbury, Basingstoke, Bromley, Lewisham, Greenwich and Croydon.
Cambridgeshire, Lincolnshire, Norfolk, Peterborough, Suffolk, East Riding of Yorkshire, Kingston upon Hull, North Yorkshire and York, meantime, received yellow alerts.
"An area of prolonged rain is moving up over the eastern region and it's not going to shift until Wednesday night," Meteo Group forecaster Gareth Harvey said. "The rain is not exclusive to the east region but that's where the persistent and largest rainfall totals of between 50 and 70mm will be."
"This means there could be some localised flooding."
Temperatures would gradually improve towards the weekend, according to weather experts, but said temperatures would still remain average for the time of year.
In February, Britain was ranked in a study as the seventh most exposed nation to economic disruption caused by flooding.