An area of low air pressure forming over northern France is rarely good news for us, as it generally means prolonged heavy rain with a north-east wind. This can be the way that a summer heatwave ends. Such a weather pattern at the start of October – as this year – is rare, but the atmosphere has behaved oddly in recent months.

A sunny morning on October 1 was deceptive. Rain arrived from the east about tea-time, becoming heavy during the night, to leave 18mm (0.7 inches) in the Wellington rain gauge by morning. It remained wet for the next three days, with further pulses of heavy rain, a clearance finally taking place after dark on October 4. The total of 61mm (2.4 inches) recorded in Wellington in some 72 hours was more than fell in the whole of September. Temperatures had hovered around the 12C (54F) mark, day and night.

After this, anything would be an improvement. On October 5 the wind picked up from the south-west, bringing warmer air and sporadic bursts of rain interspersed with drizzle. Not much better, then. On October 7 the wind eased, the sun finally came out, and the temperature in Wellington edged up to 16.5C (62F), which was more appropriate for the time of year. There was then a week of showers and sunny intervals, with winds mostly from a westerly point, and one or two chilly nights with minima near 4C (39F). Sunday 11 was by far the sunniest day of the month, for anyone fortunate enough to get out and enjoy the colours of autumn.

As a ridge of high pressure edged across us from the west during the next few days, winds veered through north to east, keeping daytime temperatures on the cool side, but we enjoyed six days without rain. By October 18 the centre of the anticyclone lay over the Baltic Sea, our region spending that day under a solid sheet of cloud with a gentle breeze from the south-east. This signalled the onset of a much more unsettled spell that would persist to the month’s end.

As the jetstream finally settled into a more normal west to east track across the Atlantic, our weather was dictated by a series of deep depressions, some of them incorporating remnants of hurricanes. October 20 was the warmest day of the month, with a maximum in Wellington of 17C (63F), thanks to a strong breeze from the south. Rain arrived before dawn the next day and was so heavy that nearly 30mm (1.2 inches) had landed in the Wellington rain gauge by 8am. This proved to be our largest October fall of rain since 2008.

Thereafter it was very much a case of chop and change, with bright showery days being interspersed with dull wet ones. A cold wind and sharp showers made October 28 rather nasty, but much warmer air returned to close the month, with gales and more heavy rain for good measure. Thanks to that, October 2020 ended up more than 50 per cent wetter than average, the total rainfall in Wellington amounting to 173 mm (6.8 inches). The mean temperature of 10.9C (51.6F) was significantly above the long-term average but it was one of the dullest Octobers so far this century.

Simon Ratsey

WWN Weather Correspondent