Blenheim still in sunshine race despite rainy October

Blenheim might have had the wettest October in a decade last month, but it is also closing in on first place in the sunshine race.

Blenheim was the sunniest town in New Zealand for the month of October, with 233.8 hours of sunshine.

The intense rain band that deluged central Blenheim on October 29.

Diana Wadsworth

The intense rain band that deluged central Blenheim on October 29.

That put the town in second place for the 2021 sunshine race, with a total so far of 2093 hours, behind New Plymouth on 2100.5 hours, and ahead of Napier on 2084.7 hours.

Marlborough Plant And Food Research scientist Rob Agnew said Blenheim had been rapidly closing the gap over winter, 52.4 hours behind New Plymouth at the end of May, but cutting that back to 7.5 hours by the end of October.

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“Hopefully with two months to go, Blenheim will take the lead and beat off all other wannabe sunniest town contenders,” Agnew said.

Yet Blenheim also had the rainiest October since 2011, recording 70.2 millimetres of rain, above the long term average of 56.8mm, calculated since 1986.

The highest daily total was on October 29, at 31.2mm according to the Blenheim Meteorological Station in Grovetown.


Blenheim stores flooded in sudden rainstorm.

However, the Grovetown station was not affected by the thunderstorm that dumped a very localised deluge on central Blenheim that evening, causing extensive surface flooding and damage to businesses.

Agnew said the Marlborough District Council’s office rain gauge, 1.75 kilometres southwest of the official Blenheim weather station in Grovetown, showed a much higher rainfall total for October 29, of 60.5mm.

The council’s data also showed the highest 60-minute rainfall total was 50.2mm, though that was not an hour-to-hour total, Agnew said.


Several people filmed the heavy rain and hail in Blenheim on the evening of October 29, 2021.

“To put that amount of rainfall into some perspective with regards to the volume of water received, the central Blenheim business district bounded by Symonds St (SH1), Maxwell Rd, Seymour St and Nelson Street (SH6) is approximately 700m by 500m which is 35 hectares,” Agnew said.

He calculated that 50.2 mm rain in one hour, over 35 hectares, equated 17.57 million litres of water dumped on this area over 60 minutes.

“Blenheim’s average October rainfall is 56.8 mm. So central Blenheim received its average October rainfall in just over a one-hour period on Friday 29 October. It is no wonder that the shop roofs, gutterings and storm water system were unable to cope with the volume of water.”

Streets in central Blenheim were awash with rainwater and hail after a thunderstorm on October 29, 2021.

The town also had above average mean temperature, at 13.9 degrees Celsius.

Agnew said from 2002 to 2012, the October mean temperature was below average every year, but since 2013, the October mean temperature had been above average for seven of the nine years.

October was usually varied in temperature from year to year, but the trend showed October had warmed by 1.1C since 1932, Agnew said.

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