How hot does a ‘heatwave’ have to be?

Some like it hot

Are heatwaves becoming a devalued currency? Last year the Met Office defined a heatwave as three consecutive days when maximum temperatures exceed the 90th percentile maximum temperature for mid-July. In London that means when the maximum exceeds 28˚C. For the rest of the south-east, as far west as Hampshire and as far north as Nottinghamshire, the threshold is 27˚C. For Dorset, Somerset, Herefordshire, Shropshire, Cheshire, Derbyshire, South Yorkshire and Lincolnshire it is 26˚C, and everywhere else, including the West Country, most of Wales, the north of England and Scotland it is 25˚C. In places it will mean a heatwave occurring in 30 to 50 per cent of years.