Statistics from the Niwa National Climate Centre showed sunlight shone on the city for a total of 618 hours between December 2017 and February 2018, and the mean air temperature at the Musselburgh weather station was 2degC above normal.
Dunedin was not the only place to have record temperatures.
Milford Sound, Ranfurly, Lauder, Te Anau, Manapouri (West Arm), Lumsden, Invercargill and Tiwai Point also had their hottest summer on record, with mean temperatures up to 2.6degC above normal.
Forecasting principal scientist Chris Brandolino said the nationwide average temperature for summer 2017-18 was 18.8degC (2.1degC above the summer average of Niwa's seven-station-temperature series which began in 1909), making it the country's hottest summer on record.
The high of 38.7degC recorded in Alexandra on January 30 was the country's hottest January temperature in 39 years.
Despite medium-scale adverse drought events being declared in Otago in January, soil moisture levels have recovered to near or above normal for the region.
Niwa data showed Dunedin received 245mm of rainfall for the summer (about 120% more than normal) - most of which fell in February.
Meanwhile, soil moisture levels in Southland remain below normal for this time of year.
A Niwa spokesman said the season was characterised by mean sea-level pressures that were higher than normal to the east and southeast of New Zealand, and lower than normal over New Zealand and to the west.
This pressure pattern delivered more frequent warm northerly and northeasterly winds than normal, consistent with La Nina conditions.
The persistence of high pressure over the Tasman Sea during November and early December prevented the mixing of cool, deeper ocean water with the surface, resulting in warmer sea-surface temperatures in the region.
''This combination and an increased frequency of northerly winds delivered unprecedented warmth to the country during summer.''
