For our ancestors, August was the first month of autumn, and hot Augusts such as in 1911 and 1947 were so exceptional as to become embedded in folklore. Only in the last 30 years has the month more regularly featured true summer warmth – if not sunshine. Our expectations have changed accordingly.

August 2020 began modestly, sunny spells and a light breeze from the west giving average temperatures. On August 5 the wind picked up from the south, feeding air from the subtropics across the British Isles, as air pressure built over the near continent. In Wellington, the temperature stayed above 15.5C (60F) that night, the first of a dozen or so in the month that would prove to be oppressively warm. The days heated up too but often with uncomfortably high humidity. Sunshine on August 8 resulted in a notable maximum of 28.5C (83F), while August 10 was dull until tea-time but nevertheless saw the mercury reach nearly 24C (75F).

Temperatures then surged in strong sunshine on August 11 and 12. A maximum of 32.3C (90.1F) on the latter date made it our hottest August day for 25 years and the fifth hottest on record in this area. Following that, the night-time minimum of 19C (66F) was our second highest ever, for any month. Unsurprisingly, a thundery breakdown ensued. Low air pressure developed over the Bay of Biscay and slowly drifted north, in time-honoured fashion. August 13 was the last hot day, cloud building in the afternoon to give distant thunder and a couple of sharp showers during another stiflingly warm night.

Thereafter, the month was basically unsettled with measurable rainfall almost every day, although warm nights remained a feature. August 14 was rather dreary, with heavy cloud on a breeze from the north-east, and 12mm (nearly 0.5 inches) of rain that night. The next two days were similarly dull, the sun finally reappearing late on August 16. Then came almost a week with comfortable daytime temperatures in the low 20s Celsius (70-73F) and fair amounts of sunshine. The exception was August 19, when heavy rain from early morning gave 18mm (0.7 inches) in the Wellington rain gauge by 10am. Further bursts of rain with thunder added another 12mm by the same time the following day.

With the North Atlantic jet stream switching to ‘autumn’ mode for the last third of the month, two named storms dictated our weather. ‘Ellen’ crossed Scotland on August 21, giving us a windy few days with another 34mm (1.3 inches) of rain in total. ‘Francis’ took a more southerly route, with damaging gales on August 25, and the very unstable atmospheric conditions in its wake resulted in torrential rain with thunder and lightning on August 27. This added another 23mm (0.9 inches) to Wellington’s total, before the wind veered to a northerly quarter. A ridge of high pressure then gave a quiet, sunny end to the month, cooler than average, but not notably so.

With a mean temperature in Wellington of 18C (64F) August 2020 was exceptionally warm. It was also among the wettest Augusts on record, our total of 122mm (4.8 inches) being more than 75 per cent above average. This unusual combination would seem to be another symptom of the way our climate is changing.

Simon Ratsey

WWN weather correspondent