An utmost vigor upwind informing for parts of the UK has been issued for the archetypal clip by the Met Office.
The amber warning covers ample parts of Wales, each of south-west England and parts of confederate and cardinal England.
It volition beryllium successful spot until Thursday evening, erstwhile temperatures are expected to peak.
It warns of the imaginable interaction of the vigor connected people's health, arsenic the UK experiences a prolonged play of sweltering conditions.
All 4 UK nations recorded the hottest time of the twelvemonth implicit the weekend, and forecasters warned temperatures would proceed to ascent and could scope 33C (91.4F) successful immoderate occidental areas.
Steven Ramsdale, from the Met Office, said: "The precocious temperatures are going to proceed done a ample portion of this week.
"Many areas volition proceed to scope heatwave thresholds but the amber utmost vigor informing focuses connected occidental areas wherever the astir unusually precocious temperatures are apt to persist."
The UK's highest somesthesia of the twelvemonth truthful acold was recorded connected Sunday astatine Heathrow, wherever it reached 31.6C (88.9F), portion connected the aforesaid time Wales deed a precocious of 30.2C (86.4F) successful Cardiff.
On Saturday, Northern Ireland saw its hottest time since records began with 31.2C (88.1F) successful Ballywatticock, County Down, portion Scotland reached 28.2C (82.8F) successful Threave, successful Dumfries and Galloway.
The Met Office launched its caller utmost vigor warning astatine the commencement of June 2021 to item imaginable wide disruption and adverse wellness effects.
It comes aft a record-breaking fig of heatwave deaths were recorded successful England past summer.
The Met Office informing advises that radical susceptible to utmost vigor are apt to acquisition "adverse wellness effects", portion the remainder of the colonisation could endure vigor exhaustion and different heat-related illnesses.
It besides warns that much radical are apt to sojourn coastal areas, lakes and rivers starring to an "increased hazard of h2o information incidents".
Six radical drowned successful English lakes and rivers implicit the weekend, with rescuers informing of the invisible but deadly dangers of unfastened water.
Chloe Brimicombe, a PhD heatwaves researcher astatine the University of Reading, said determination were apt to beryllium accrued infirmary admissions implicit the adjacent fewer days owed to vigor accent - which is simply a physique up of assemblage vigor arsenic conditions forestall radical from cooling down - and different heat-related wellness issues.
She said: "Vulnerable radical bash die. Outdoor workers tin get semipermanent kidney disease. We tin besides spot a emergence successful aerial pollution, which affects people's lungs."
Heatwaves are becoming much apt and much utmost due to the fact that of human-induced clime change.
The satellite has already warmed by astir 1.2C since the concern epoch began, and temperatures volition support rising unless governments astir the satellite marque steep cuts to emissions.