A heatwave warning has been issued for Sussex.
The Met Office has declared a Level 2 Heath-health alert for Friday through to Sunday morning for across the south east and other parts of England.
The warning is triggered when the Met Office forecasts there is a 60% or higher chance of temperatures being high enough on at least two consecutive days and the intervening night to have a significant effect on health.
The highest temperatures are likely on Friday, followed by a very humid night.
Heavy thunderstorms are also predicted for Saturday, which may lower temperatures slightly, but it will still be very humid.
Paul Cosford, director for health protection at Public Health England, said: “While many people enjoy hot weather, high temperatures can be dangerous, especially for people who may be particularly vulnerable such as older people, young children and those with serious illnesses.
“Everyone can enjoy the sun safely by keeping out of the heat at the hottest time of the day, avoiding sunburn and staying hydrated with plenty of cool drinks.
“Older people and those with long-term illnesses are particularly vulnerable to the effects of very hot weather, so it’s important to look out for them and keep indoor areas as cool as possible.”
Met Office deputy chief meteorologist Steve Ramsdale said: “We’ve got hot and humid air moving up from the continent which will see temperatures rise through to the weekend, with some high day and night-time temperatures expected by Friday.
“The humidity will make it feel close, muggy and uncomfortable for many in the heat and people should take steps to keep cool – particularly across the areas where we have issued a heat health alert.”