Press Release May 2017

Weather Data summary for May 2017 for the Blenheim Meteorological station located at the Grovetown Park campus of the Marlborough Research Centre.

May 2017 recorded well above average sunshine, cooler than average temperature and slightly below average rainfall


205.4 hours sunshine for May was 121% of the long-term average for May of 169.6 hours (1930-2016).

May 2017 is now the fourth sunniest May on record for Blenheim for the 88 years 1930 – 2017.

May 2016 recorded 167.8 hours sunshine

May 2015 recorded 214.5 hours sunshine (sunniest May on record 1930-2016)

May 2014 recorded 199.1 hours sunshine

May 2013 recorded 182.5 hours sunshine

Blenheim has recorded 1103.6 hours sunshine for the five months January to May 2017; 104% of the long-term average of 1066.2 hours.

Blenheim is currently sitting in second position behind Whakatane, for total sunshine hours so far in 2017. Richmond is hard on Blenheim’s heals.

 Sunshine totals for 2017 (up to 30th May)

Whakatane                1137.5 hours

Blenheim                  1095.1 hours (42.4 hours behind Whakatane)

Richmond                 1080.3 hours (14.8 hours behind Blenheim)

Tekapo                      1068.7 hours

Appleby                    1020.8 hours

Nelson                        983.8  hours (111.3 hours behind Blenheim)


Rainfall total of 57.2 mm was 90% of the long term average for May of 63.6 mm (1930-2016)

May 2016 rainfall was 89.2 mm.

May 2015 rainfall was 20.0 mm.

May 2014 rainfall was 16.0 mm.

May 2013 rainfall was 94.4 mm.

The first five months of 2017 have recorded significantly more rain than in 2015 and 2016

Total rainfall for the five months January to May 2017 was 324.6 mm; 129% of the long-term average of 251.0 mm.

Total rainfall for the five months January to May 2016 was 248.8 mm; 99% of the long-term average of 251.0 mm.

Total rainfall for the five months January to May 2015 was 129.0 mm (51% of the LTA);

 Soil Moisture

High rainfall in the first half of April 2017 meant that the soil moisture at the beginning of May was substantially higher than in 2015 and 2016. Soil moisture (5-35 cm depth) on 1 May was 32.3%.

With a number of rain events during May, and little evaporation, soil moisture on 31 May had risen to 36.1%. This is close to field capacity for the top soil at this site.

Average soil moisture for May 2017 was 35.4%, compared to the average of 31.6%.


Mean temperature of 10.4°C was 0.8°C below the long-term average temperature for May of 11.2°C (1986-2016).

May 2016 mean temperature was 12.6°C

May 2015 mean temperature was 11.4°C

May 2014 mean temperature was 11.8°C

The mean temperature of 10.4°C for May 2017 is the coolest May mean temperature in the five years 2013-2017. The previous coolest May is 2012, which recorded a mean temperature of 9.8°C.

If you are scratching your head thinking that May wasn’t colder than average there is a partial explanation supplied when we look at the average daily maximum and minimum temperatures.

The average daily maximum was only 0.5°C below average, whereas the average daily minimum was 1.0°C below average; i.e. the cooler than average night time temperature in May dragged the mean temperature down more than the slightly below average day time temperatures.

 May 2017 temperatures and frosts for Blenheim

Mean Max Mean Min Mean  Deviation


Total Ground Frosts Total Air Frosts
1-7 May 17.1 3.4 10.3         -0.9 1 0
8-14 May 16.7 7.0 11.8        +0.6 1 0
15-21 May 14.8 4.7   9.7         -1.5 1 1
22-28 May 15.4 4.4   9.9         -1.3 2 0
29-31 May (3 days) 16.1 4.2  10.2        -1.0 0 0
1-31 May 2017 16.0 4.8 10.4         -0.8 5 1
Long-term average


16.5 5.8 11.2 5.6 1.4

 Average May temperatures for Blenheim (1932-2017) and the trend in May temperature

 The graph indicates how the average May temperature has risen in Blenheim over the past 86 years. However, while May 2017 was below average for the period 1986-2016, it was by no means cold, when compared to many previous years. The graph does show that there has been a lot of variation in May temperatures over the 11 years 2007 to 2017; i.e. May 2007 is the warmest on record, whereas May 2009 was one of the coolest.

All months May to September have shown considerable warming over the last 30 years. However, the months October to April have shown little increase in temperature; i.e. Blenheim’s late autumn, winter and early spring temperatures are much warmer than they used to be, whereas the late spring, summer and early autumn temperatures have shown little change.


May 2017 – 5 ground frosts and 1 air frost.

May 2016 – 2 ground frosts and 0 air frosts

May 2015 – 8 ground frosts and 3 air frosts

 The coldest morning during May 2017 was the 21st, with an air minimum of -1.5°C and a grass minimum (ground frost) of -5.0°C.

Wind Run

May 2017 recorded an average of 183.5 km of daily wind run, well below the long-term average of 218.6 km (1996-2016). May 2016 recorded average daily wind-run of 283.3 km; i.e. 154% of the May 2017 wind-run.

Rob Agnew

Plant & Food Research /Marlborough Research Centre

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Filed under Blenheim Weather Data, Weather Press Releases.

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