The heatwave currently sweltering the UK is expected to last until at least Friday, according to the Met Office.
The mercury will continue to sizzle above 30C this week, as some regions may see some respite today with thunderstorms.
It comes as Met Office issued a Level 3 - Heatwave Action for large swathes of England and warn there is a 90 per cent possibility these conditions will remain in some areas until 9am on Friday.
Temperatures are widely expected to meet or exceed heat-health alert thresholds for the next three days.
Yesterday, the Met Office issued its first ever amber Extreme Weather Warning.
It covers a large part of Wales, all of South West England and parts of southern and central England.
It has now also been extended to Northern Ireland from Wednesday morning through to midnight on Friday as temperatures could reach 33C.
Public Health England has also extended its heat-health alert until Friday as they urge those in the heatwave hotspots to exercise caution.
Dr Owen Landeg, Scientific and Technical Lead at PHE, said: "Everybody can be affected by high temperatures and most people are aware of good health advice for coping with hot weather.
"However, it’s important to keep checking on those who are most vulnerable such as older people and those with heart or lung conditions.
"As we experience the first hot weather episode of the year, it’s important for everyone to remember to adapt their behaviours. This is particularly important during the pandemic with many people self-isolating."
The North East will get some reprieve this week with clouds along the coasts before going inland and pushing south by Wednesday.
The hottest parts of the East are expected to be today and Wednesday.
In the West, regions will continue to boil on Thursday. The Met Office also expects isolated thunderstorms to hit today.
A yellow thunderstorm warning has been issued for parts of Central and South East England.
The warning will last from 1pm to midnight on Tuesday.
The forecaster warned the downpours could cause disruption to travel while flooding to home and business may happen "quickly".
Floodwater, lightning strikes, hail or strong winds could also cause damage to some buildings, while some areas could see 30-60mm of rainfall in just one or two hours.
Chief Operational Meteorologist at the Met Office Steven Ramsdale said: "The high temperatures are going to continue through a large part of this week, with temperatures regularly in the high 20s and low 30s Celsius by day, along with high overnight temperatures.
"Many areas of the UK will continue to reach heatwave thresholds, and whilst the highest temperatures are likely to be in central and southern parts of the UK, some of the most unusually high temperatures are likely to be seen over parts of the West, particularly over Northern Ireland.
"There’s also a continuing risk of isolated thundery downpours late in the afternoons but most should stay dry until later in the week.
"Temperatures should fall for most areas into the weekend along with some more unsettled conditions also looking to develop."
