Niwa National Climate Centre meteorologist Ben Noll said the Musselburgh weather station recorded a temperature of 28.5degC, between 1pm and 2pm on Sunday — the highest April temperature since records began in 1947.
It was nearly 2degC warmer than the previous high which was 26.6degC, set on April 8, 1955.
"I think you blasted it out of the park. It was a substantial record-breaker."
Oamaru also set an April temperature record when the mercury reached 27.5degC — the highest since records began in 1967.
The town’s previous record was 26.9degC, set on April 4, 2005.
Several other places around Otago also had hot days, but not record-setters.
Mr Noll said the hot temperatures were mainly on the east coast of Otago and were caused by strong northwest foehn winds.
Foehn winds occur when an air mass hits the Southern Alps, dries out as it travels over the mountains, and then warms up again as it travels down the other side.
"The origins of the air mass that was over New Zealand at the time stretched all the way back to the deserts of Western Australia.
"That air came across Australia, right across the Tasman Sea, hit the Southern Alps and then returned to the same state that it was in over Australia.
"You can look at the previous records and you can see we had a very similar set-up in 1955 to generate that record day.
"But in the year 2021, we live in a warmer climate and thus we’re more likely to hit those higher numbers."
Mr Noll believed it would be warm for the rest of the week.
"I don’t think it will be to the same level as we had on Sunday, but it will be above average temperatures over the next five days.
"Beyond that, I think we will cool down a little bit in the middle part of the month, but over the next three months we will have average to above average temperatures on the east coast of the South Island."
Cooler-than-average temperatures would be short-lived and not the theme, he said.
