The Met Office has issued a warning that more than half a month's worth of rain could fall across southern England on Friday, raising the risk of flooding.
Forecasters predict that around 30mm to 40mm (1 to 1.5in) of rain will fall in certain areas within a six-hour span.
In a typical August, approximately 63mm (2.5in) of rain falls across southeast England for the entire month.
A yellow thunderstorm warning has been issued for a significant portion of the West Midlands and the South of England.
The Met Office has cautioned that there is a potential for travel disruptions, and there is a possibility of flooding affecting homes and businesses, along with lightning strikes and potential power outages.
The warning, covering regions from Birmingham to London, and across the entirety of the South East and Solent area, is in effect from 06:00 BST until 12:00.
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Media caption, Watch: The latest UK weather forecast for your location
Among the events cancelled due to Friday's forecast is the Tall Ships parade of sail in Falmouth, Cornwall.
Organizers have stated that the safety and well-being of the vessel crews are their top priorities.
Meanwhile, coastal areas of north and mid-Wales are under a yellow wind warning from midnight until 18:00.
A period of strong easterly winds could bring gusts of up to 60mph, and more widely, around 40-50mph.
The Met Office has indicated that bus and train services may be affected, and there's potential for damage to trees and temporary structures such as marquees and tents.
Met Office meteorologist Rachel Ayers explained that showers are expected to commence in the southwest of England and south Wales, gradually intensifying as they move eastward.
"Given that it is the summer holidays, people are more likely to be outdoors and traveling for vacations," she stated.
"There's a chance that driving conditions could be impacted, leading to longer travel times.
"Please follow advice from our partners like the RAC regarding driving in heavy rain if you decide to make the journey."
Conditions are expected to improve on Saturday with sunny intervals, although accompanied by showers and gusty winds. Heavy rainfall is more likely to be confined to northeastern Scotland. Photo by Richard Knights, Wikimedia commons.