Temperatures have been recorded in the Tauranga area at several sites during the last 100 years, including the current Tauranga Airport site from June 1990.
It's very common for areas such as Tauranga to have had different observation sites during the years – and the readings from the earlier sites have been adjusted to the present site using standard climatologically procedures.
The temperature series, as shown in the graph, are based on the data from the original observations from the various sites as available on the NIWA National Climate Database archive, with data from the sites prior to the Tauranga Airport site being adjusted, where appropriate, to temperatures which are likely to have been recorded at the current airport site.
Traditionally, temperature observations have been recorded with a set of maximum and minimum temperature thermometers.
These record the daily maximum temperature (usually recorded in mid-afternoon), and the daily minimum temperature (usually recorded just before dawn).
The graph shows details of the average daily maximum temperatures (called simply ‘afternoon'), for Tauranga for April from 1913-2018. Note April 1947 and 1964 are not included because of incomplete data.
The long-term average afternoon temperature in April for Tauranga for is 20.0 degrees Celsius, ranging from the cool April months of 1925, with an average afternoon temperature of 18.2 degrees Celsius, and 1923 with an average afternoon temperature of 18.3 degrees Celsius, to the warm April months of 1938 (22.2 degrees Celsius), and 1916 (22.1 degrees Celsius).
The graph of the average afternoon temperatures for April shows generally normal variations from April to April, but several of the last 20 April months have been a little warmer than other April months.
From 1913 to 2017, there have been 15 April months with an average afternoon temperature of 21.0 degrees Celsius or more, and eight April months with an average afternoon temperature of less than 19.0 degrees Celsius.
The value for April 2018 was 19.9 degrees Celsius,
The 15 warmest April months – in terms of afternoon temperatures – on record, in chronological order, are 1916, 1924, 1928, 1935, 1938, 1948, 1955, 1956, 1978, 1981, 2010, 2012, 2013, 2014, and 2016. In contrast, the eight coolest April months – in terms of afternoon temperatures – on record, in chronological order, are 1923, 1925, 1940, 1941, 1949, 1980, 1991 and 1992.
The average afternoon temperatures for Tauranga for the 50 years 1914-1962, and the 50-year period 1963-2011 are both 20.0 degrees Celsius.
For further information see the following textbooks books (all available at specialised libraries)
"The Value of the Weather" (1970), "The Uncertainty Business - Risks and Opportunities in Weather and Climate" (1986), "The Human Impact of Climate Uncertainty - Weather Information, Economic Planning, and Business Management " (1989), all by W.J.Maunder