Hot conditions will not hit the 40.3C reached last month but could last longer, forecasters say.
The UK is set for another heatwave this week with highs of up to 35C (95F) in some parts, forecasters have said.
The Met Office said while conditions would be below the 40.3C recorded last month, the hot weather could last for a longer period.
More parts of England are also facing hosepipe bans amid very dry conditions, as fire crews warn of wildfires.
A heatwave is defined as above average temperatures seen for three days or more.
Met Office meteorologist Tom Morgan said a “fairly widespread heatwave” was developing across the UK this week with the peak of the temperatures likely to be on Friday or Saturday.
“It does look like a prolonged period of dry weather and obviously that’s bad news for southern England where some rain would really be useful now,” he said.
Temperatures will build from 28C or 29C on Tuesday and reach the low to mid-30s from Thursday, Mr Morgan said.
He said the West Midlands and West Country could see with highest temperatures with a maximum of around 35C, but this is uncertain.
A heat health-alert has been put in place from midday on Tuesday until 18:00 BST on Saturday for all regions of England, UK Health Security Agency has said.
This alert is designed to help healthcare professionals manage through periods of extreme temperatures.
There have also been calls for more hosepipe bans to be brought in.
On Sunday, Environment Secretary George Eustice urged more water companies to impose hosepipe bans.
It comes as Southern Water already imposed a hosepipe ban for customers in Hampshire and on the Isle of Wight, and from Friday South East Water will do the same for customers in Kent and Sussex.
Welsh Water has also announced a ban for Pembrokeshire and Carmarthenshire later this month.
‘Wild fire risk increases’
Dave Walton, deputy chief fire officer at West Yorkshire Fire and Rescue Service, warned the minimal rain raised the risk “quite significantly” of further wild fires happening across the UK.
Describing the threat, he said: “Wild fire will literally spread faster than people can run, but also it’s just careless disposal of cigarettes, just driving along a road throwing one out of the window of a car, that can start a wild fire.
“It’s things like broken glass, literally magnifying the effect of the sun and starting a wild fire. There’s a number of things.”
- A CULTURE OF FEAR?: A closer look at £2bn ‘punk’ brewery business BrewDog
- FROM BOY TO MAN TO PRIME MINISTER: The story of Boris Johnson as told by those who know him best