Yellow heat health alerts are now in force with temperatures expected to hit 34C (93F) in parts of the UK this weekend.
The alerts, issued by the UK Health Security Agency, external, cover central, southern and eastern parts of England and are valid until 15 July.
They warn that hot weather could have impacts on vulnerable people and the health and care services that support them.
This looks set to be the most widespread and persistent spell of hot weather so far this year with all four nations set to meet their heatwave criteria – perhaps for five or six days in places.
High pressure brings high temperatures
An area of high pressure will be moving across the UK giving increasing amounts of sunshine.
As that high shifts eastwards a flow of winds from continental Europe will develop and temperatures will start to climb.
On Thursday and Friday parts of England and Wales will get into the low thirties Celsius, with Scotland and Northern Ireland seeing highs of 24-27C (75-81F).
The heat will build further over the weekend with maximum temperatures of 33 or 34C (91-93F) in southern England and the Midlands – although some eastern coasts will be a little cooler thanks to winds from the chilly North Sea.
Scotland, Northern Ireland, Wales and England are all likely to see a heatwave
Parts of Northern Ireland are forecast to hit 27C (81F) and temperatures of 30C (86F) are possible in Scotland.
This is in contrast to this summer’s previous two heatwaves which were mostly focused across the south and east of England.
However, it looks unlikely that we will exceed the highest temperature of the year so far, 35.8C (96.4F) at Faversham, Kent on 1 July.
As humidity builds, the nights will also turn warm and muggy which could make it uncomfortable for sleeping.
The heat will be accompanied by dry weather which will be unwelcome news for some.
Hosepipe bans come into force in Yorkshire on Friday with Thames Water also warning that restrictions will be necessary if the water shortage does not improve.
It fits in with a pattern of hot and dry weather that has been gripping much of western and southern Europe so far this summer – with wildfires burning in southern France as well as parts of Greece and Spain.
Climate change is making heatwaves more frequent and more severe.
Analysis by scientists at Climate Central, external suggests the high temperatures predicted for the UK over the next few days have been made three to five times more likely by climate change.
Met Office data shows that all of the UK’s ten warmest years on record have occurred since 2000 – with five in the last decade. Those records go back to 1884.
How long will it last?
As well as being more widespread than our previous two hot spells, this heatwave also looks like it will go on for longer.
High temperatures are forecast to last into Monday, especially in southern and eastern parts.
Some places will see five or six days of heatwave conditions
A weather front is then expected to push in from the west, bringing outbreaks of rain, possible thunderstorms, and slightly cooler conditions for many.
Beyond that there is uncertainty in the forecast with some computer models suggesting temperatures close to 30C returning by the end of next week – and others bringing a change to something more unsettled.
You can keep up to date with the temperatures where you are on the BBC Weather app – and check the prospects for the rest of the summer with our monthly outlook.
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