The UK Health Security Agency (UKHSA) has issued an amber heat health alert for London.
This means the potential for a significant impact on health and care services is expected.
The alert, which also covers the South West and East of England, is in effect from Thursday afternoon (June 18) until 8pm on Tuesday (June 23).
The UKHSA website explains that an amber heat health alert indicates a likely increase in demand on all health and social care services by vulnerable populations.
It also warns of an increased risk to health for individuals aged over 65 years or those with pre-existing health conditions.
The alerting system is designed to provide early warning when adverse temperatures are likely to impact the population's health and wellbeing.
The Met Office predicts temperatures will climb into the high 20s across the country later this week, with 30C potentially being reached in southern parts of England by Friday.
By Saturday, some areas in the south and south-east of England are likely to meet heatwave criteria, with temperatures possibly reaching 32C in the warmest locations.
The Met Office defines a heatwave as three consecutive days with daily maximum temperatures meeting or exceeding the heatwave temperature threshold.
This threshold varies by county, with London and its surrounding counties having a threshold of 28C.
On Sunday, the warmest parts of the eastern Caribbean island of Barbados are expected to see temperatures fluctuate between 26C and 30C.
The Met Office has also indicated that the south and south-east of England could become even hotter on Monday, potentially reaching 33C in some areas.
While the temperatures rise, spells of rain are also predicted, especially across northern and western areas, with a slight chance of thunderstorms across south-eastern England.
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