The Met Office has extended the yellow warning for heavy rain and thunderstorms across the whole of East Anglia.
Its warning of the risk of localised flash flooding and hail along with potential for disruption to travel and power supplies.
The weather warning is valid until 9pm on Wednesday 20 July 2016
The Met Office says areas of heavy thunderstorms will continue to affect parts of Scotland and northern England into this afternoon before slowly clearing away northeast.
However isolated heavy thunderstorms may still develop across Scotland and parts of England, including some central, eastern and southeastern areas, this afternoon and this evening.
The Met Office said: "Whilst most places will miss the worst, please be aware of the risk of localised flash flooding. Frequent lightning, large hail and strong winds could be additional hazards. All of this could lead to some flooding of homes, businesses and transport networks. Disruption to power is also possible."
"Hot, moist air spreading north and northeast across the UK today will produce thunderstorms, initially organised within large areas of rain before becoming more isolated this afternoon.
"Rainfall will be very variable, but some places could see around 30 mm in an hour and more than 50 mm in a few hours.
"The thunderstorms later this afternoon are likely to be most widespread across northern England and Scotland, and it is here that there is the greatest risk of disruption.
"Further south, they will be much more isolated, with disruption less likely, across the rest of England."
Last-minute voters had to struggle through tricky weather conditions to make it to polling stations in Norwich this evening.
Torrential thundery downpours saw flash flooding on many of the city's streets.
Water was up to a foot deep close to the polling station in Cadge Road in the west of the city although it didn't stop voters from casting their ballots
Video from Jamie Brown
Heavy rainfall caused severe disruption to passengers travelling in from Norfolk, Suffolk and Essex into London this morning.Read the full story ›
Drive safely and avoid floodwater on the roads. Just a few inches of water is enough to stop your car and leave you stranded. Don't risk it.
Make sure you stay safe on the roads. Don't drive into flood water, it can float your car or cause a loss of control https://t.co/7YS2dkxEMN
16:30 Norwich to London Liverpool Street will now run as scheduled.GK
Due to heavy rain flooding the railway at #ManorPark services between Liv St, Ipswich and Norwich are being disrupted. GK
Last night and this morning Essex experienced an exceptional amount of rainfall in a short period of time.
With a Met Office amber warning in place and more rain forecast for later this afternoon and into the evening, motorists are being advised not to travel unless their journeys are absolutely necessary.
Heavy rain has affected four locations.
These locations are:
- A127 Fortune of War roundabout, Laindon
- Parkway, Chelmsford
- Howe Green under A12
- A414 at Writtle, outside Hanging Gardens Garden Centre
Some schools have been forced to close today due to flooding. These include:
- Margaretting Church of England, Ingatestone
- Monkwick Infant School and Nursery, Colchester
- St Peter's Church of England, Chelmsford
- The Ongar Academy, Ongar
Updates can be found here
The Met Office has issued an amber "be prepared" weather warning for southern parts of the Anglia region as more thundery downpours are forecast.
The whole region is covered by a yellow "be aware" weather warning.
The amber weather warning is in force in parts of Hertfordshire and Essex from 3pm until 11pm on Thursday 23 June 2016.
The yellow weather warning is valid until 2am on Friday 24 June 2016 and covers the entire Anglia region.
The Met Office is warning of possible disruption to travel and localised flooding as well as frequent lightning.
The Met Office says there is a risk of thunderstorms affecting the London area this afternoon and evening.
Although some areas will miss them, potentially intense thundery downpours are likely elsewhere in the Anglia region this afternoon and evening before they clear later this evening or during the early hours of Friday.
"Another wave of thunderstorms breaking out across southeastern UK this afternoon and evening is likely to bring some thunderstorms into the London area.
"Whether these storms are as severe as those of last night is, at this stage, uncertain, but in view of storms being expected during the afternoon and evening impacts may be as widespread as those of last night and first thing this morning.
"Warm and humid air has spread into roughly the southeastern quarter of the UK, bringing with it a risk of thunderstorms this afternoon and evening. Where thunderstorms occur torrential rain and frequent lightning are expected.
"30 mm or more of rain could fall in an hour and locally in excess of 50 mm is possible in two or three hours."