The Met Office has issued yellow alerts for thunderstorms with warnings of travel disruptions.
Thunderstorm warnings have been issued for parts of Northern Ireland until 8pm today, Northeast England for Friday afternoon and for much of England from tomorrow evening through Saturday afternoon.
Met Office chief meteorologist Jason Kelly said: "More warnings could be issued for the weekend and early next week. Keep an eye on the Met Office forecast for updates as the picture develops.
“Within the warm and humid airmass we will potentially see temperatures reaching 30C or more for parts of eastern England by Friday, with very warm and muggy conditions continuing into the weekend in parts of central and southern England."
MET OFFICE
|The thunderstorm warning in place for Friday
On Sunday, widespread showers and thunderstorms are expected to continue, moving northwards across the UK throughout the day.
Forecasters suggest there will be some drier and brighter spells between the showers and it will feel warm or very warm in sunshine, particularly in the east and southeast.
Looking ahead to next week, the unsettled pattern is expected to continue, with showers and thunderstorms at times, although some drier, brighter interludes are also likely.
Temperatures will be near normal or warm for the time of year, depending on sunshine.
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PA
|There could be thunderstorms and lightning on the way
By mid-week, conditions may begin to settle from the west, though eastern areas could still see showers.
Temperatures are expected to be near or slightly above normal, with warmth in sunnier areas.
Many will be hoping for relief from the lack of rain over the last few weeks with many places declaring hosepipe bans.
Environment Agency Director for Water and National Drought Group chair Helen Wakeham said: "This has been the driest start to the year since 1976."
Rainfall across England was 20 per cent less than the long-term average for June, which was also the hottest on record for the country.
Two heatwaves driving unusually high demand for water, the Environment Agency has said.
Drought was declared in East and West Midlands on Tuesday, with the region joining swathes of northern England in drought status.
Yorkshire Water became the first major water company to bring in a hosepipe ban which came into effect last Friday.
South East Water has announced a hosepipe ban in Kent and Sussex from Friday, and Thames Water is bringing in a ban from next Tuesday