Londoners bracing for the London sixth heatwave of a record-breaking summer may have a brief window of relief before the heat returns, but forecasters are already pointing at late September as the next flash point. The city has already endured five heatwaves this season, with temperatures peaking at a sweltering 38.1C, making this the hottest summer ever recorded in the capital.
The current cooler stretch, complete with rain and duvet-worthy nights, is welcome. But Met Office long-range forecasts suggest it will not last. Their outlook for the period from 30 August to 13 September notes ‘there is a chance that late-season hot spells or heatwaves develop, especially in the south’. Temperatures are expected to be near normal at first, ‘but may turn warmer later with a chance of some hot periods in the south’.
Crucially, the signals for any sixth heatwave in later September are, in the Met Office’s own words, ‘very weak’. Forecasters are candid that it is probably too soon to pin down an exact date, or to say with any confidence whether the heat will materialise at all. Early autumn also carries the risk of thunderstorms and flooding alongside whatever warmth arrives, and September as a whole is forecast to bring a mixture of showers and hot spells before settling into ‘drier, more settled weather, especially in the south and east’ through the second half of the month.
A summer that rewrote the record books
To understand why forecasters are watching the autumn so closely, it helps to grasp quite how unusual this summer has been. According to the Met Office’s own deep-dive into July’s weather, the number of days exceeding 30C this summer had already equalled the long-standing benchmark set in 1995, and that milestone was reached with much of August and early autumn still ahead. That figure alone gives a sense of the relentless accumulation of heat this season has delivered.
Offshore, the picture is equally out of the ordinary. BBC Weather reports that the seas around England and Wales are currently running at up to 3C above their seasonal average. Warmer seas feed back into the atmosphere, raising the baseline from which any incoming heat event begins, and they help sustain humid, unsettled conditions well into what should be cooler months.
The Met Office’s long-range outlook for September, October and November adds a further note of caution for anyone hoping autumn will draw a clean line under the heat. The forecast identifies ‘an increased risk of heatwaves and heat-related impacts especially during the first half of the period’. That language, applied to months traditionally associated with harvest festivals and morning mist, would have seemed extraordinary in almost any previous year.
London sixth heatwave: was any of this predictable?
In one sense, yes. BBC Weather notes that both the Met Office and MeteoGroup predicted back in June that the summer would run hotter than average, with an increased likelihood of heat spikes and heatwaves. What neither model foresaw quite so precisely was the sheer accumulation of events, five named heatwaves in a single season, each one adding to the civic and physiological fatigue felt across London and the wider south-east.
Meteorological summer officially ends on 31 August, a date BBC Weather flags as the close of the three-month season that runs from June through August. By any measure, this one will be defined by heat long after the calendar moves on. Whether the sixth episode arrives in the form the forecast hints at, or whether the ‘very weak’ signals simply dissipate, the Met Office has made clear it will continue to monitor the pattern closely as the outlook sharpens through the coming weeks.
The next formal update to the long-range forecast, covering the August-to-September transition, will offer the clearest steer yet on whether London’s sixth heatwave is a genuine meteorological event in waiting or a statistical ghost that fades with the season.