Parts of flood-hit Wales are braced for a further drenching, with three weeks worth of rain forecast to fall in just two days.
A yellow weather warning is in place across a swathe of the country, with up to 90mm of rainfall due over Monday and Tuesday.
Wales has been badly hit by flooding in recent weeks.
Last month, the Prince of Wales visited communities facing massive repair and clean-up operations in the Rhondda Cynon Taf area.
But more bad news is on the way, the Met Office said on Sunday.
Meteorologist Greg Dewhurst told the PA news agency: “Through Monday it will be a fairly bright start but we will see rain spread in from the west by the afternoon.
“Then we will see heavy rain right through the rest of Monday, overnight and into Tuesday morning.”
In Wales, the average rainfall for March is 117mm, meaning the worst affected areas could see three-weeks worth of rain in just over 24 hours.
“The ground is already saturated and with all the rainfall we have had over recent weeks it is likely to lead to further flooding in places.”
A yellow weather warning indicates flooding to some homes and businesses is likely, transport is likely to be disrupted and there is a risk of spray and standing water on the roads.
A similar warning is in place for the north of England, including the cities of Leeds, Bradford, Wakefield and Huddersfield, with a projected 50mm of rain – a little under half the monthly average for March – due to fall.
While there are no weather warnings in place for the later half of the week, there will be widespread showers, meaning flood-hit areas will get little respite.
On Sunday, Boris Johnson was heckled when he visited the town of Bewdley in Worcestershire on the River Severn which saw some of the worst flooding in the country in February.
The Prime Minister has been heavily criticised for failing to visit flood-hit communities during the crises.
Some onlookers shouted “traitor” as he looked at the flood defences.
He said during the visit it was “too easy” for a PM to “come to a place in a middle of an emergency”, but that it was “not so easy, frankly, for the emergency services”.
“What they have to do is then break off and gold command has to find somewhere to brief you, everybody has to gather. They’re diverting from their work for hours and hours,” he said.
“What I’ve been doing since the flooding began is coordinating the national response but also looking at what we can do in the next months and years to ensure this country really is ready to cope with the impacts of flooding.”