The Met Office has issued a yellow weather warning as England and Wales are both facing a barrage of rain.
The warning is in place from 3pm today until 6pm tomorrow and will cover the entirety of both nations.
Flooding is "likely" to a few homes and businesses, with areas expected to be hit the worst by disruption and delays being Bedfordshire, Buckinghamshire, Cambridgeshire, Essex, Hertfordshire, Norfolk, Northamptonshire and Suffolk.
There is particular concern for the River Severn in various spots in Gloucestershire and several warnings and alerts are in place across Oxfordshire, including points along the River Thames.
Flooding is expected in many areas
PA
Meanwhile, the River Dene in Walton, Warwickshire, has already experienced some flooding.
A Met Office statement said: "An area of persistent and occasionally heavy rain is expected to move from west to east across the warning area during Saturday and Sunday, falling on already saturated ground.
"Rain will clear western areas early Sunday, whilst rate of clearance from east and southeast England is open to some uncertainty, but all areas should become dry by evening."
Some interruption to power supplies is also expected, with the Met Office urging residents to be prepared.
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The River Dene in Walton, Warwickshire, has already experienced some flooding
PA
"People cope better with power cuts when they have prepared for them in advance.
"It’s easy to do; consider gathering torches and batteries, a mobile phone power pack and other essential items."
People have been told to keep up to date with the weather forecast in their area.
"Be prepared for weather warnings to change quickly: when a weather warning is issued, the Met Office recommends staying up to date with the weather forecast in your area", the statement added.
Residents have also been urged to check if their property is at risk of flooding and if so, to consider preparing a "flood plan".
They have also been urged to check road conditions before embarking on their journeys.
Natural Resources Wales said: "Local flooding from surface water is probable, and local flooding from rivers is also possible, on Saturday and Sunday across Wales.
"Land, roads and some properties could flood and there could be travel disruption."