A new record has already been set in Wales, which saw its highest late August bank holiday temperature (27.4C) on Saturday.
Southeasterly winds drew warm air from Europe towards the UK on Friday, bringing a heatwave and dry weather for the weekend.
One million people are expected to attend the two-day carnival in west London this year.
“On Saturday and Sunday, there’ll be plenty of sunshine, especially in the east, with temperatures rising into the mid to high twenties Celsius for many – it’ll be warmest in southeastern parts where 31-32C (87.8-89.6F) is likely,” Andy Page, chief meteorologist at the Met Office, said.
- Read more
“Western parts are likely to see more cloud, and a probable cooling trend through the weekend.”
Health warnings for the heatwave have been issued for east and southeast England.
Public Health England has advised the public to look out for anyone who may be particularly vulnerable to the ill-effects of hot weather, such as older people, young children and people with heart and lung conditions.
The Met Office has said temperatures on Monday are likely to be lower than those over the weekend, with the warmest weather confined to the southeast.
Unsettled weather, with rain and showers at times, is expected to return in the northwest at the start of next week.
The severity of the heatwave will vary across the country, with highs of just 26C expected in Glasgow compared to a maximum temperature of 31C predicted in London over the weekend.
Earlier this year, the UK saw its highest officially recorded temperature of 38.7C and joined Belgium, Germany and the Netherlands in the list of countries that have broken their national records this year.
July 2019 was also the hottest month ever recorded in history, according to the World Meteorological Organisation.
“If we do not take action on climate change now, these extreme weather events are just the tip of the iceberg. And, indeed, the iceberg is also rapidly melting,” Mr Guterres said.
“Preventing irreversible climate disruption is the race of our lives, and for our lives. It is a race that we can and must win.”
Additional reporting by PA