The city recorded a top temperature of 34degC at 11am, according to the MetService, before a forecast southerly blocked the sun and temperatures tumbled.
The conditions mirrored those across the South, with Timaru topping 40degC and St John reporting several calls there to people fainting from the heat.
MetService forecaster Stephen Glassey last night put the heat down to the Foehn effect, in which a moist northwest wind flows over the mountains, drying out and getting hotter as it goes.
But the southerly had put its stamp on the climate by noon, when the temperature in Dunedin had dropped to 22degC.
Other centres to melt in the heat yesterday were Christchurch, Alexandra, Ashburton and Oamaru, which all officially reached 36degC.
In Oamaru, that 36degC heat had dropped 15degC in 18 minutes as the southerly swept through.
The MetService showed Queenstown's high at 29degC, Wanaka at 25degC, and Gore 27degC.
The heat was connected to the same heat wave which left Sydney reeling in 42degC heat on Saturday followed by its hottest recorded night where the temperature reached 27.6degC.
