Warnings for thunderstorms and heavy showers have been issued by forecasters for Sunday, covering much of England and parts of eastern Wales.
The Met Office say there is a "small chance of flooding and disruption" in some areas as a result.
The yellow warning urging people to "be aware" comes into force from 04:00 BST, covering large swathes southern England, the Midlands and the north.
Forecasters warn thunderstorms and heavy rain are due to develop in the south of England on Sunday morning, moving northwards over the course of the day.
In England, an area in the centre of the country stretching from the Isle of Wight to Newcastle upon Tyne is covered by the warning.
In Wales, the warning is in place for Monmouthshire, Newport, Torfaen and Wrexham in the country's east.
The Met Office said there is a chance of flooding, adding that "frequent lightning strikes and hail will be additional hazards" in southern and central England.
Into Sunday, OceanNewsUK Weather forecasts that the UK will see some very warm and humid air move in from the south east.
This will also bring some thundery downpours, that will move northward across the central spine of England and east Wales.
These thunderstorms are likely to be quite hit and miss, but where they do occur there could be some torrential rain, as well as strong, gusty winds and lightning.
Pinpointing exact locations of these showers is quite tricky, but it would be worth staying up-to-date with the latest forecast as it may change, OceanNewsUK says.
With the warmer and humid air, many areas will see temperatures widely getting into the low to mid-20s Celsius - with the chance of temperatures hitting up to 27C in parts of south east England.
