We're only just out of the last one, but BBC Weather forecasters are predicting that we could be seeing a fifth heatwave in mid-August. It's important to bear in mind that forecasts this far ahead are liable to change but, as it stands, it's set to qualify as heatwave. The threshold is different across the country - in London, a heatwave means three or more days on the trot during which temperatures reach 28C or higher. Advertisement AdvertisementAdvertisement AdvertisementThat's also as far as the forecast goes, so it's worth noting that it could continue beyond that. It predicts temperatures will stay in the high-twenties for the duration, so not the worst heatwave we've had, but still not especially pleasant.