A yellow alert warning has been issued for the capital from 9am on Friday to 9am on Monday June 12 by the UK Health Security Agency (UKHSA) as well as many other parts of the UK.
The Met Office has also issued a yellow alert for thunderstorms in London on Saturday from 2pm to 9pm.
Temperatures are set to reach a high of 25C in London on Friday and a scorching 31C on Saturday, with a chance of heavy showers or thunderstorms developing later on Saturday.
The showers are forecast to continue on Sunday and Monday, and are expected to be heavy and thundery at times. Temperatures are set to stay warm during the nights as well.
A yellow alert has also been issued in the North East, North West and Yorkshire and Humber.
A yellow alert issued on Wednesday in West Midlands, East Midlands, East of England, South East and the South West was escalated to an amber alert on Thursday.
“Weather impacts are likely to be felt across the whole health service, and at this level we may begin to see some health impacts across the wider population, not just the most vulnerable,” the UKHSA said.
Both yellow and amber alerts remain in place from 9am on Friday 9 June to 9am on Monday 12 June.
Under the new HHA system introduced by UKHSA and the Met Office, a yellow alert means more demand on health care services by vulnerable people is expected, and over 65s, or those with pre-existing health conditions, are at an increased risk.
