The Met Office has warned what's expected to come amid a 34-hour weather warning for thunderstorms.
The East of Bristol, South Wales and most of the South West are gripped by the alert, which will be in place from 11am and 9pm tomorrow (September 8).
A second weather warning is also in place for large parts of England and Northern Ireland from Thursday, between 11am and 8pm.
READ MORE: New UK 'heatwave' with 28C temperatures predicted after two-day weather warning
The Met Office said: "Mainly dry for many areas Wednesday but there is a chance of heavy rain and lightning bringing some disruption."
The warnings come after a spell of hot weather for large parts of England this week thanks to a plume of hot air from the Azores.
Temperatures have nudged towards 30C in Bristol, parts of Somerset, Gloucestershire and the south east of England.
Netweather.tv also predicts more warm weather next Wednesday and Thursday (September 15-16).
Met Office on what to expect
- There is a small chance that homes and businesses could be flooded quickly, with damage to some buildings from floodwater, lightning strikes or perhaps hail
- Spray and sudden flooding could lead to difficult driving conditions and some road closures
- Where flooding or lightning strikes occur, there is a chance of delays and some cancellations to train and bus services
- There is a small chance that some communities become cut off by flooded roads
- There is a slight chance that power cuts could occur and other services to some homes and businesses could be lost
