The Met Office has issued a amber weather warning for "extreme heat" in Hertfordshire.
Forecasters are warning of "adverse health effects are likely to be experienced by those vulnerable to extreme heat" due to rising temperatures towards the end of this week.
The mercury is set to hit 30C on Thursday in St Albans and 31C in northern Hertfordshire on Thursday, August 11 - when the amber warning is due to take effect.
It is due to stay in place across Friday and Saturday - with highs of 32C in some parts of the county - until Sunday, August 31.
Temperatures are due to cool on Monday, with a 50 per cent chance of rain in the evening according to today's forecast (Tuesday, August 9).
A Met Office statement reads: "A hot spell will develop across parts of England and Wales later this week.
"Expect adverse health effects are likely to be experienced by those vulnerable to extreme heat.
"The wider population are likely to experience some adverse health effects including sunburn or heat exhaustion (dehydration, nausea, fatigue) and other heat related illnesses.
"Some changes in working practices and daily routines likely to be required.
"An increased chance that some heat-sensitive systems and equipment may fail."
The amber weather warning covers a large portion of the southern half of the UK.
It includes the East of England - including Hertfordshire, Bedfordshire, Cambridgeshire and Essex.
The warning also covers London and cities further afield - including Birmingham, Bristol, Cardiff, Leeds and Manchester.
The warm temperatures follow record-breaking dry July weather.
England received just 35pc of its average July rainfall in 2022.
A new hottest temperature record for Hertfordshire was set on July 19 in Buntingford, East Herts at 39.2C, beating the previous 37.9C record set at Aldenham, near Watford on August 10, 2003.
A Hertfordshire water firm has urged residents not to leave it "high and dry" by overusing water.
An Affinity Water spokesperson said: "During autumn and winter last year, there wasn't as much rainfall as normal, so our groundwater levels are below average.
"There are no current restrictions, but it's important to use water wisely."
They urged residents to avoid hosepipe use, turn off the tap while brushing teeth, and fill up washing machines before turning them on instead of running half washes, although no restrictions are in place.
On the railways, Network Rail has warned it may need to introduce speed restrictions if drought impacts the soil beneath the rails, or if hot rails are at risk of expanding and "buckling".
A spokesperson said: "Hot weather can affect the rails, overhead power lines and the ground which the track sits on.
"We work hard to get you to where you need to go, safely and on time by minimising the impact of hot weather on the railway."
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