The yellow alert is in place across the whole of England apart from the north-east, most likely until 9pm on Sunday.
Oli Claydon, a spokesperson for the Met Office, told the PA Media news agency: “We will see sunny conditions through the week with cloudless skies, and some high temperatures by the time we get to Wednesday and Thursday, where we could see 31, maybe 32C.
“The high temperatures are quite widely spread across the UK, although the highest temperatures are probably somewhere in south-eastern England spreading out to central parts of England as well.
“[It could be] a warm night overnight on Wednesday, with the potential for temperatures not dropping below 20C, which is what we term a tropical night.
“That’s most likely in the southern half of the UK and more likely in urban areas where the temperatures obviously stay up that little bit higher overnight. Then as we move through to Thursday, another hot day with highs of 31 to 32. And again, another warm night with potential for a tropical night on Thursday.”
On Monday, temperatures reached 30C and we can expect Tuesday to hit 32C.
Average temperatures are expected to return by the middle of next week.
Here’s what the warning means, along with what the other heatwave levels stand for.
What do the Met Office’s heatwave levels mean?
The Met Office will sometimes issue weather warnings if temperatures exceed certain levels. These are predominantly to help healthcare services and workers.
“Should thresholds for an alert be reached outside of this period, an extraordinary heat-health alert will be issued and stakeholders are advised to take the usual public health actions,” the Met Office website states.
There are five levels in place, here’s what they are and what they mean:
The first level entails long-term planning to avoid the risks and complications involved with heatwaves, along with “year-round joint working to reduce the impact of climate change” and discovering ways to adapt to the temperatures.
It mainly exists to remind authorities of the importance of and need for planning ahead for the warmer periods.
Level 1 – Green – Summer preparedness and long-term planning
The Met Office uses level 1 throughout summer to stay vigilant as temperatures rise. Social and healthcare services will be working to ensure that they are prepared for extreme weather.
Level 2 – Yellow – Alert and readiness
The level 2 alert is rolled out when the risk is “60% or above for threshold temperatures being reached in one or more regions on at least two consecutive days and the intervening night”.
This is when social and healthcare services will be on high alert and working to try to ensure the heatwave does not cause harm to people and patients.
Level 3 – Amber – Heatwave action
The Met Office has triggered a level 3 heatwave warning to parts of the UK. This is when the threshold temperature has been reached for one full day and the following night, while the following day also has a 90% chance of hitting the threshold temperature again.
Healthcare and social services and workers will now be taking action to protect high-risk groups who may not fare well in soaring temperatures.
According to the NHS website, those most at risk include:
Older people – especially those over 75
Those who live on their own or in a care home
People who have a serious or long-term illness – including heart or lung conditions, diabetes, kidney disease, Parkinson's disease or some mental health conditions
Those who may find it hard to keep cool – babies and the very young, the bedbound, those with drug or alcohol addictions or with Alzheimer's disease
People who spend a lot of time outside or in hot places – those who live in a top-floor flat, the homeless or those whose jobs are outside
Level 4 – Red – National Emergency
The fourth and final warning level means a heatwave has continued for so long at such high temperatures that its effects “extend outside the health and social care system”.
The Met Office warns that death and illness may occur among the fit and healthy at this stage, as well as in high-risk groups.