A heatwave in the UK is defined by the Met Office as at least three consecutive days with daily maximum temperatures exceeding a county-specific threshold, reflecting a sustained spell of unusually hot weather.
The heatwave threshold temperature varies across the UK. In Greater London it is 28C whereas in Northern Ireland and Scotland it is 25C.
It is likely that a few places could meet the heatwave definition during Friday, Saturday and Sunday. At the moment, areas such as London and the south Midlands are most likely to see this.
With the unseasonable warmth expected to continue into Tuesday and beyond, more parts of England and Wales could experience a heatwave after the bank holiday weekend.
