Press Release January 2018

Meteorological data summary for January 2018 for the Blenheim Meteorological station located at the Grovetown Park campus of the Marlborough Research Centre.

Weekly temperatures, rainfall and sunshine during January 2018

Mean Max


Mean Min








1st – 7th 24.8     (+1.4) 15.2      (+2.5) 20.0    (+1.9) 50.0 47.6
8th – 14th 23.3     (-0.1) 14.4      (+1.7) 18.9    (+0.8) 19.4 39.7
15th – 21st 26.4     (+3.0) 17.0      (+4.3) 21.7    (+3.6) 10.2 65.6
22nd – 28th 25.7     (+2.3) 16.7      (+4.0) 21.2    (+3.1) 0.0 62.8
29th – 31st    (3 days) 28.2     (+4.8) 17.8      (+5.1) 23.0    (+4.9) 0.8 27.9
1st – 31st December 25.4 (+2.0°C ) 16.0   (+3.3°C) 20.7  (+2.6°C) 80.4   180% 243.6   93%
LTA 1986-2017 23.4 12.7 18.1 44.6 262.5

January 2018 was very warm. Sunshine hours, evapotranspiration and wind-run were all below average. Rainfall was well above average.

Air Temperature

The mean temperature of 20.7°C was 2.6°C above the long term average temperature for January of 18.1°C (1986-2016).  

The January 2018 mean temperature has entered the record books as the hottest January in Blenheim for the 87 year period 1932 to 2018. The previous hottest January was in 1935 with a mean temperature of 20.6°C

 The mean temperature of 20.7°C has also equalled Blenheim’s previous hottest ever month – February 1998, which also recorded a mean temperature of 20.7°C.

 January 2017 mean temperature was 18.4°C

January 2016 mean temperature was 18.8°C

January 2015 mean temperature was 18.8°C

January 1935 mean temperature was 20.6°C (previous highest January mean temperature)

 Despite the very high daily mean temperature for January 2018, Blenheim only surpassed 30.0°C on two days; 31.2°C on the 20th and 32.5°C on the 30th. There were no days above 30°C in January 2017.

There were an additional 16 days when the maximum temperature was between 25 and 30°C. The lack of days above 30°C is largely a function of how close Blenheim is to the coast. Slightly further inland the maximum temperatures are higher; e.g. The weather station at Woodbourne exceeded 30.0°C on four days during January 2018. The maximum temperature on 30 January at Woodbourne was 34.1°C.

 The maximum temperature of 32.5°C on 30 January 2018 in Blenheim was the hottest day since 6 February 2011, which recorded 33.4°C.  Blenheim’s hottest day on record for the 70 years 1948-2017 is 11 January 1979 with 36.0°C.

 If you think January 2018 was hot in Blenheim, spare a thought for Cromwell in Central Otago. Cromwell recorded 21 days during January 2018 when the maximum temperature exceeded 30.0°C. The average daily maximum temperature for January 2018 was 30.0°C, which was 4.6°C warmer than Blenheim’s average maximum temperature.


243.6 hours sunshine for January is 93% of the long term average for January of 262.5 hours.

January 2017 sunshine was 282.0 hours

January 2016 sunshine was 232.8 hours

January 2015 sunshine was 297.0 hours


Rainfall total of 80.4 mm is 180% of the long term average for January of 44.6 mm.

January 2017 rainfall was 27.2 mm.

January 2016 rainfall was 69.2 mm.

January 2015 rainfall was   3.2 mm.

January 2014 rainfall was 79.2 mm.

Blenheim received only 70.4 mm rain for the three months October, November and December 2017; 46% of the long-term average. At the beginning of January 2018 Marlborough was greatly in need of rainfall with very dry conditions and low river levels. Fortunately much needed rainfall was received on a number of days between the 4th and 12th January and again on the 17th.

 Soil Temperatures

Soil temperatures are recorded at four depths at the Grovetown Park weather station. The three shallow soil temperatures at 10, 20 and 30 cm depth, were much further above average during January 2018 than the deeper soil temperature at 100 cm depth. It takes a long time for the deep soil to heat up and also to cool down.

10 cm – 21.0°C (+2.0°C)

20 cm – 21.4°C (+1.3°C)

30 cm – 22.3°C (+1.5°C)

100 cm – 18.8°C (+0.4°C)


Average daily wind-run in January 2018 was 190.6 km, well below the long-term average (LTA) of 274.3 km (average wind speed of 7.94 km/hr, compared to LTA of 11.43 km/hr).

The average daily wind-run of 190.6 km recorded in January 2018 is by far the lowest January total on record for Blenheim for the 33 period 1986 to 2018.

In marked contrast January 2017 was very windy with average daily wind-run of 336.3 km; (average wind speed 14.0 km/hr); i.e. January 2018 recorded only 57% of the wind-run recorded in January 2017.

Potential evapotranspiration

Total potential evapotranspiration for January 2018 was 135.6 mm, 95% on the long-term average. Despite the warm temperatures, the evapotranspiration was kept fairly low due to the lack of wind, lower radiation and higher relative humidity.

In contrast January 2017 recorded 181.3 mm evapotranspiration, by far the highest January total on record for the 22 years 1997-2018.

Potential water deficit

This is the difference between monthly rainfall and potential evapotranspiration.

80.4 mm rainfall – 135.6 mm potential evapotranspiration = -55.2 mm potential water deficit

This is a low total for January in comparison to the long-term average of -99.7 mm

In contrast the potential water deficit in January 2017 was -154.3 mm, the highest on record 1997-2018

 Shallow soil moisture (topsoil)

Average shallow soil moisture (0 to 35 cm) at the Grovetown Park weather station for January 2018 was 28.1%. This is the highest January average for the 16 years 2003 to 2018 (period of record). However, on 2 January the topsoil moisture was only 15.5%, slightly above its driest point. Rainfall from the 4th to the 13th January boosted soil moisture from 15.5 to 35.8%. The result of this rapid increase in soil moisture was to bring unirrigated lawns and pasture back into life with a flush of mid-summer growth. A further 10 mm rain on 17 January gave topsoil moisture a top up, helping to prolong the grass growth.

Plant & Food Research / Marlborough Research Centre

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