Temperatures are expected to peak at 31C in London at 3pm on Monday, August 3, according to new Met Office maps. Manchester is forecast to reach 29C and Cardiff 28C.
The Met Office forecast for Monday says: "Rain affecting much of Scotland on Monday, some heavy. Scattered showers across Northern Ireland and other western areas, though most of England and Wales fine with some hot sunshine. Humid."
Four regions under amber heat alert
The UK Health Security Agency (UKHSA) has issued four amber heat health alerts covering London, the East Midlands, the East of England and the South East. The warnings run from 9am on August 3 until 9am on August 5.
The alerts warn that soaring temperatures could increase pressure on health and social care services, putting vulnerable people at risk. The UKHSA said there could be a rise in deaths, particularly among those aged 65 and over or with health conditions.
The agency also warned of indoor environments overheating, raising the risk to vulnerable people living independently in community and care settings, as well as a potential for water-related incidents including cold-water shock and drowning.
What an amber alert means
The Met Office explained: "An amber alert would represent a situation in which the expected impacts are likely to be felt across the whole health service, with potential for the whole population to be at risk and where other sectors apart from health may also start to observe impacts, indicating that a coordinated response is required.
"In addition, in some circumstances a National Severe Weather Warning Service (NSWWS) Extreme Heat warning may be issued in conjunction with and aligned to the HHA. This situation would indicate that significant impacts are expected across multiple sectors."
