Heavy downpours are lashing parts of Britain and the weather is expected to get even worse, with thunderstorms and flooding predicted.
Flooding at homes and businesses in parts of south east England on Monday is "likely", the Met Office said as it upgraded weather warnings in the region.
Forecasters have said rain which swept across the UK overnight was likely to worsen with heavier downpours expected.
Yellow rain warnings for some parts of the south east, including London, were heightened to amber shortly before midday on Monday, with the worst conditions expected later in the afternoon and into the evening.
"Homes and businesses are likely to be flooded, causing damage to some buildings," the Met Office said, adding 50-60mm of rain could fall in four to six hours.
"Delays and some cancellations to train and bus services are likely with spray and flooding probably leading to difficult driving conditions and some road closures."
Fast flowing flood water "causing danger to life", power cuts and thunderstorms are also possible, forecasters said.
A wider yellow rain warning which spans an area of eastern England from the Humber all the way down to the south coast remained in force.
Warnings are expected to be lifted in parts of the south east by Tuesday but a yellow alert spanning much of eastern England up to the Scottish border is currently in place until Thursday.
The heaviest rain overnight was recorded in Sellindge, Kent, where 0.6in (15mm) fell in 12 hours, the Met Office said.
Forecaster Steven Keates said the northern Home Counties, East Midlands, Lincolnshire and Humber could see some of the heaviest and most persistent rain.
"Probably later this afternoon into this evening and tonight we could see some of the heaviest rain," he said.
He added: “The rain started to push in overnight as expected but nothing particularly heavy so far.
“The heaviest and most persistent rain is still to come.
“Probably later this afternoon into this evening and tonight we could see some of the heaviest rain.
“It is going to be more the persistence of the rain in some places and the intensity for others.
“Eastern and southern England in particular are likely to be seeing long and persistent bad weather.
"It is going to be more the persistence of the rain in some places and the intensity for others.
"Eastern and southern England in particular are likely to be seeing long and persistent bad weather.
"Some places could see a month's worth of rain in two or three days, and we could see some flooding issues."
Steve Ramsdale, duty chief meteorologist at the Met Office, said: “The development of weather conditions leading to thunderstorms and intense rainfall can happen extremely quickly, creating a challenge for forecasters.
“We have been able to indicate the likelihood of further spells of heavy rainfall for the rest of the week, but the exact details will remain uncertain until nearer the events.”
The Environment Agency (EA) has one flood alert on the River Ravensbourne in London covering the boroughs of Lewisham, Bromley, Greenwich and Croydon.
It said there was a risk of flooding for low-lying land, gardens and roads that are close to the river between 7am and 6pm.
The EA added: "We are actively monitoring the situation and are prepared to respond if required.
"Please avoid using low-lying footpaths near local watercourses and plan driving routes to avoid low-lying roads near rivers, which may be flooded."
The band of rain will move slightly north and west before settling, with Northern Ireland and Scotland expected to see the best of the weather.
Weather warnings are in place for the whole of Tuesday and up until midday on both Wednesday and Thursday for north-eastern England down to the Wash and as far west as the West Midlands.