Updated: 2026-08-28
If you lived in central London in early August 2020, you didn't imagine it: that was the hottest week the city has experienced since Met Office records began at St James's Park in 1912. Between Thursday 6 August and Wednesday 12 August, the daily maximum temperature averaged exactly 33.67°C. At the heart of that sweltering stretch, on Friday 7 August, the thermometer peaked at 36.1°C — the highest single reading within that record-breaking week.
To put those figures in perspective, compare them with the long-term seasonal climate at St James's Park. The average daily maximum for August across the full 1912–2025 series sits at 22.3°C, and the average daily mean for the month is 18.0°C. For an entire week to push the daily maximum average more than 11 degrees above the August norm is not a small anomaly — it is an outlier of extraordinary magnitude, one that has not been matched in any other week across more than a century of measurements.
The week of 6–12 August 2020 stands alone at the top, but it didn't happen in isolation. The same region of the calendar produced the second and third hottest weeks, all three clustered within an eight-day window. Only the legendary summer of 1976 comes close to challenging them. Here are the five warmest weeks on record at St James's Park:
| Week Starting | Week Ending | Average Daily Maximum (°C) |
|---|---|---|
| 2020-08-06 | 2020-08-12 | 33.67 |
| 2020-08-07 | 2020-08-13 | 33.51 |
| 2020-08-05 | 2020-08-11 | 32.57 |
| 1976-06-24 | 1976-06-30 | 32.56 |
| 1976-06-23 | 1976-06-29 | 32.33 |
Notice how the top three weeks of 2020 overlap almost entirely. The 6–12 August window and the 7–13 August window share six of their seven days. The 5–11 August window shares five. That means the period from 5 to 13 August 2020 contained not one, not two, but three of the five hottest weeks ever recorded in London — a remarkable concentration of extreme heat in a single stretch of nine days.
The summer of 1976 remains the only other serious contender, with two consecutive weeks in late June averaging above 32°C. For over four decades, those June weeks of 1976 stood as London's hottest. The 2020 event not only surpassed them but did so decisively, with the top week exceeding the best 1976 week by more than a full degree.
What made that particular week so extreme? The daily maximum peaked at 36.1°C on 7 August, but the week's defining characteristic was not just its single hot day — it was the relentless consistency. For day after day, the maximum temperature refused to drop below the mid-30s, keeping the seven-day average exceptionally high. A single hot day can spike; a sustained week of heat requires a weather pattern locked firmly in place, with high pressure dominating southern England and drawing hot continental air northward across the capital.
That the record was set in August is also notable. While July is London's warmest month on average — with a daily maximum of 22.6°C and a daily mean of 18.3°C — the city's most extreme heat events have historically favoured late June and early August. The 1976 weeks occurred in June; the 2020 weeks arrived in August. Across the full climate series, the monthly averages show August running just behind July: 22.3°C for the daily maximum and 18.0°C for the daily mean. The 2020 event therefore arrived right at the peak of the seasonal cycle, and then pushed far beyond anything the seasonal norm would suggest.
To fully appreciate the extremity of that August week, here is the full monthly pattern at the station. These are the long-term averages against which every individual week — including the record-breaker — is measured:
| Month | Average Daily Maximum (°C) | Average Daily Mean (°C) |
|---|---|---|
| January | 7.7 | 5.2 |
| February | 8.2 | 5.5 |
| March | 10.9 | 7.5 |
| April | 13.9 | 10.0 |
| May | 17.7 | 13.4 |
| June | 20.8 | 16.3 |
| July | 22.6 | 18.3 |
| August | 22.3 | 18.0 |
| September | 19.7 | 15.7 |
| October | 15.5 | 12.1 |
| November | 10.9 | 8.1 |
| December | 8.6 | 6.1 |
Look at the gap between the record week and the monthly averages. In August, the normal daily maximum is 22.3°C. The 2020 record week ran at 33.67°C. That difference of over 11 degrees — the gap between a pleasant summer's day and a heatwave of rare severity — is precisely what made that week historic. Even the coldest month at St James's Park, January, has a daily maximum of 7.7°C; the 2020 record week was running more than four times that number.
And what of the single hottest day within that week? The 36.1°C recorded on 7 August 2020 stands as the peak of the most intense seven-day stretch London has ever seen. It is the kind of reading that, before 2020, would have seemed almost unthinkable for the British capital. The fact that it arrived not as an isolated spike but as part of a sustained, week-long surge of heat is what places the 6–12 August 2020 period in a category of its own.
As the climate continues to evolve, records like this one invite a sober question: how long will it remain the hottest week on record? The Met Office's continuous dataset at St James's Park, running from 1912 through 2025, will hold the answer. For now, London's most intense week of heat is firmly established — 6 to 12 August 2020, with an average daily maximum of 33.67°C and a peak of 36.1°C.
Source: Met Office — St James's Park station, London. Data period: 1912–2025.
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