The Met Office has issued its verdict on a potential sixth heatwave of the year, and whether September could be the month to bring it. Much of the UK has endured a summer of droughts and heatwaves, with the summer on track to be the hottest on record and to deliver the worst harvest in records stretching back decades.
Heatwave definition and criteria
In the UK, a heatwave is officially defined by the national forecaster as a location recording at least three consecutive days with daily maximum temperatures meeting or exceeding a specific regional threshold. The criteria range from 25C to 28C depending on the county.
There have been five heatwaves in the first eight months of the year.
September 5 to 19 forecast
The Met Office's long-range forecast for September 5 to 19 says that while temperatures are expected to stay around average for the time of year, there could be some hot periods in the south. However, many areas are due for showers and thunderstorms before the dry weather returns later in the month.
The forecast reads: "Most likely changeable at first with showers or longer spells of rain across many areas, perhaps heavy and thundery in places.
"Further into September, drier weather may become more prevalent, especially in the south and southeast, with any more unsettled conditions tending to become confined further north and northwest.
"Temperatures will probably be near normal at first, but may turn warmer later with a chance of some hot periods in the south."
El Niño impact
This comes after experts warned that an unprecedented El Niño event is set to bring more storms and rain to the UK. El Niño is declared when sea temperatures in the tropical eastern Pacific rise 0.5C above the long-term average, impacting global rainfall patterns and temperatures, with sea conditions in such an event typically between 1C and 2C above average.
But the natural warming of sea temperatures in the region is forecast to reach more than 3C in the coming months, making this year's event "the largest since the 19th century", according to the Met Office. North-western Europe – including the UK – is likely to experience wetter and stormier conditions in the coming autumn and early winter, the forecaster said.
