London could be hit by thunderstorms as it frazzles in its third heatwave of the year.
The Met Office said there was a risk of showers and possibly thunderstorms on Friday and Saturday.
The prospect of more lightning erupting in the skies above the capital came as health chiefs upgraded their warning about the latest heatwave.
Temperatures could soar to 34C in the city on Monday, with a daily peak of at least 30C possible until Sunday.
As the capital baked, Thames Water urged Londoners to stop using their hosepipes to water their gardens and clean their cars.
The UK Health Security Agency (UKHSA) said existing yellow heat-health alerts for London, the South East, the South West, the East of England and the Midlands were being escalated to amber.
The higher level warning will be in place from 9am on Wednesday 8 July until 9pm on Sunday 12 July.
The yellow heat-health alerts will remain in place until then.
Dr Agostinho Sousa, head of extreme events and health protection at UKHSA, said: “Sustained periods of warm weather can result in serious negative health outcomes across the population, so it is important that everyone takes sensible precautions while enjoying the sun.
“Based on the current forecast, we don’t currently expect the health impacts to be as high as the heatwave we saw at the end of June but older adults and those with pre-existing conditions are still at risk.”
He added: “If you have friends, family, or neighbours who are more vulnerable, it is important to check in on them and ensure they are aware of the forecast and are following the necessary advice.
“Simple steps such as staying hydrated, avoiding the sun during the hottest part of the day, and keeping your home cool are effective ways to help keep yourself and others safe during periods of hot weather.”
A yellow alert highlights that significant impacts are “possible” across health and social care services due to high temperatures, including a rise in deaths, particularly among those aged 65 and over or with health conditions. There may also be impacts on younger age groups.
It also raises the prospect of:
* A likely increase in demand for health services
* Internal temperatures in care settings (hospitals and care homes) may exceed the recommended threshold for clinical risk assessment
* Heat may affect the ability of the workforce to deliver services
* Indoor environments may overheat increasing the risk to vulnerable people living independently in community and care settings
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* Swimming and other water-related incidents may increase, including risks from cold‑water shock and drowning
An amber alert warns of the same risks but says they are “likely” rather than just “possible”.
It also highlights that some health staff may struggle to get to work due to transport issues, other sectors could be impacted due to travel delays, demand for power may exceed capacity, and there may be issues managing medicines.
The last rain recorded in London was on June 27 when thunderstorms hit the city.
A Met Office spokesman said: “There is a risk of showers or possibly thunderstorms across the London area this Friday and Saturday, this is an aspect of the forecast that still has some uncertainty and will be monitored through the week.”
If there is no rain on Friday or Saturday, the next precipitation could be on July 18th, and even then it could be just drizzle, according to the BBC Weather forecast.