Press Release August 2017

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

August 2017 mean temperature was well above average, with fewer frosts than average. Rainfall and sunshine hours were close to average. Wind-run was well below average.

Temperature

Mean temperature of 10.3°C was 1.3°C above the long-term average temperature for August of 9.0°C (1986-2016).

August 2016 mean temperature was 8.3°C.

August 2015 mean temperature was 9.2°C.

August 2014 mean temperature was 8.6°C.

August 2013 mean temperature was 10.8°C. Second warmest on record

August 2017 is now the third warmest August on record for Blenheim for the 86 year period 1932-2017, with mean temperature of 10.34°C. The warmest August on record is 2009 with a mean of 10.85°C and the second warmest is 2013 with a mean of 10.77°C.

It is very interesting to note how much warmer August has generally been since the turn of the new millennium.  Of the 18 years 2000 to 2017, fourteen of those years have recorded warmer August mean temperatures than in the 79 year period 1932 to 2000.

Although the mean temperature for August 2017 was well above average, the mean temperature in the first week was well below average (Table 1). However, from the second week onwards the weekly mean temperatures were all well above average.

Table 1: Weekly weather data during August 2017

Mean Max

(°C)

Mean Min

(°C)

Mean

(°C)   Deviation

Ground

Frosts

Air

Frosts

Rainfall

(mm)

Sunshine

(hours)

1st – 7th 13.4 2.3 7.8        (-1.2) 3 2 1.8 35.8
8th – 14th 16.0 7.4 11.7      (+2.7) 0 0 27.8 31.1
15th – 21st 15.6 4.6 10.1      (+1.1) 1 0 20.4 46.8
22nd – 28th 17.0 4.7 10.8      (+1.8) 3 1 7.6 59.7
29th – 31st     (3 days) 15.6 9.1 12.4      (+2.4) 0 0 8.2 11.5
1st – 31st August 2017 15.5

(+1.3)

5.2

(+1.3)

10.3       (+1.3) 7

(3.5 less)

3

(0.8 less)

65.8

(105%)

184.9

(103%)

August LTA

(1986 – 2016)

14.2 3.9 9.0 10.5 3.8 62.5 178.8

LTA – Long Term Average

The coldest day was 4th August, with a minimum air temperature of -1.3°C and a ground minimum of -4.6°C. (Not quite as cold as 9th August 2016 which recorded a minimum air temperature of -2.1°C and a ground minimum of -5.1°C).

Winter temperatures

The following table of winter temperatures and ground frost numbers gives a quick indication of how the winter of 2017 compares with the previous four years 2013 to 2016.

Table 2: Winter temperatures and ground frosts for the five years 2013 to 2017 compared to the long-term average

June July August Mean or Total
Mean Temp 2013 (°C) 8.9 9.1 10.8 9.6 °C
Mean Temp 2014 (°C) 10.8 7.5 8.6 9.0 °C
Mean Temp 2015 (°C) 9.0 7.5 9.2 8.6 °C
Mean Temp 2016 (°C) 10.1 8.7 8.3 9.0 °C
Mean Temp 2017 (°C) 8.8 8.0 10.3 9.0 °C
LTA Mean Temp (°C) (1986-2016) 8.7 7.9 9.0 8.5 °C
 
Ground Frosts 2013 11 18 6 35
Ground Frosts 2014 2 16 13 31
Ground Frosts 2015 13 19 9 41
Ground Frosts 2016 10 12 10 32
Ground Frosts 2017 10 13 7 30
LTA Ground Frosts (1986-2016) 12.06 15.13 10.45 37.6
 
Mean Ground Frost Temp 2013 (°C) -2.2 -2.5 -1.7 -2.3
Mean Ground Frost Temp 2014 (°C) -1.3 -3.0 -2.7 -2.8
Mean Ground Frost Temp 2015 (°C) -2.7 -3.4 -2.8 -3.1
Mean Ground Frost Temp 2016 (°C) -2.2 -2.9 -3.2 -2.8
Mean Ground Frost Temp 2017 (°C) -1.9 -3.5 -3.5 -3.0

LTA – Long Term Average

The first two months of winter 2017 (June, July) both recorded mean temperatures that were close to average (+0.1°C). However, as detailed above, the last month of winter, August 2017 was well above average. The consequence of warmer winter mean temperatures over recent decades is that Blenheim is continuing to record far fewer frosts than earlier in the 20th century. The winter of 2017 recorded 30 ground frosts compared with the long-term average of 37.6 (1986-2016). However, in contrast the long-term average number of ground frosts from June to August, for the period 1932 to 1985 was 52.6.

Figure 1 displays the total number of ground frosts recorded for the three winter months (June, July, August), for the 86 year period 1932 to 2017. The blue line indicates that the total number of frosts can vary markedly from year to year. The yellow line indicates that the 10-year moving mean has largely been decreasing, notwithstanding that there was a slight increase from 2004 to 2010. The red trend line starts out at 61.9 winter ground frosts in 1932, however by 2017 this has dropped to 31.9; i.e. In 2017 Blenheim is only recording approximately half as many winter frosts as it did in 1932.

Figure 1. Ground frosts recorded in Blenheim (1932-2017) during winter (June, July, August)

Soil Temperatures

Soil temperatures were well above average for August as a consequence of the warm air temperature.

10 cm mean soil temperature = 8.8°C; 2.3°C above average

20 cm mean soil temperature = 9.5°C; 1.9°C above average

30 cm mean soil temperature = 9.8°C; 1.3°C above average

100 cm mean soil temperature = 10.6°C; 0.6°C above average

Sunshine

184.9 hours sunshine for August is 103% of the long term average for August of 178.8 hours (1930-2016).

August 2016 recorded 191.1 hours sunshine.

August 2015 recorded 187.7 hours sunshine.

August 2014 recorded 179.9 hours sunshine.

August 2013 recorded 150.2 hours sunshine.

August 2011 recorded 235.0 hours sunshine.  Highest total on record (1930-2015)

August 1941 recorded 129.2 hours sunshine.  Lowest total on record (1930-2015)

Total sunshine for Blenheim for the eight months January to August 2017 is 1608.2 hours, or 103% of the long-term average of 1556 hours.

Sunniest town in New Zealand

At the end of July Blenheim was sitting in third position behind Whakatane (+40 hours) and Richmond (+5 hours). Blenheim was the sunniest town in August and has now moved into second position overall, currently 32 hours behind Whakatane and 12 hours ahead of Richmond.

Rainfall

Rainfall total of 65.8 mm for August is 105% of the long-term average for August of 62.5 mm (1930-2016). Although August may have felt as if it was a wet month, it only received average rainfall. Rain was recorded on 13 days spread throughout August, which probably gave the feeling that it was wet. However, the highest daily rainfall total was only 13.8 mm on the 14th.

August 2016 rainfall was 39.2 mm.

August 2015 rainfall was 49.8 mm.

August 2014 rainfall was 9.8 mm.

August 2013 rainfall was 65.4 mm.

August 2012 rainfall was 123.2 mm.

August 1969 rainfall was 4.9 mm – driest on record

August 1990 rainfall was 172.1 mm – wettest on record

Total rainfall for Blenheim for the eight months January to August 2017 is 471.2 mm or 108% of the long-term average of 437.0 mm.

Total winter rainfall (June, July, August) for Blenheim was 146.6 mm, 79% of the long-term average of 186.0 mm. The below average 3-month total was because June was dry, with only 18.4 mm rain.

Moisture Deficit

Moisture deficit is the difference between rainfall received and evapotranspiration lost. The moisture deficit is in Marlborough is in a much better position going into the new season than in either 2015 or 2016; i.e. the moisture deficit in 2017 is lower than in 2015 or 2016.  Rainfall from January to August 2017 is 170 mm higher than for January to August 2015, and 72 mm higher than for January to August 2016. High rainfall in April 2017 is largely responsible for the lower deficit to the end of August 2017.

Wind

Average daily wind run for August 2017 was 215 km, with an average wind speed of 8.96 km/hr. The long-term average wind-run for August is 235.7 km (1996-2016).

August was yet another calmer than average month. The only month to have recorded above average wind-run so far in 2017 is January, which was very windy.

Outlook for the new grapegrowing season

With August having been warmer than in any of the past three years (2014, 2015, 2016) and with warmer than average soil temperatures, we currently expect that budburst of grapes in Marlborough could be slightly earlier than it was in the last three years. However, as 50% budburst of Sauvignon blanc in central Rapaura normally occurs in the first week of October, the September temperature will have a big influence on the date of budburst.

Budburst of Chardonnay has just started in Gisborne this week, and indications are that it is slightly earlier than in the last three years.

Plant & Food Research / Marlborough Research Centre

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