Metservice described it as "a Föhn wind", or hairdryer in German, that was "transporting air from higher in the atmosphere and warming it up significantly as it descended over the mountains northwest of Timaru".
Metservice meteorologist Clare O'Connor told Morning Report a narrow band of warm air and warm moist air was dumping a bunch of rain in the southwest and around the glaciers area.
"As it is hitting the mountain range, it lifts up, as it lifts up, it dries out, as everything drops as rain.
"And then as it descends down on the eastern side of the Alps, it heats up faster as it doesn't have the water in there anymore.
"So this narrow band passing over just happens to be aligned with where Timaru is."
It was quite unsual, she said.
"One time last year, it went from a single digit up into the high teens in the early hours of the morning in Timaru again."
Earlier today, in Oamaru temperatures hit 24.5 deg C at 2am, but a change in winds has cooled the place down to about 16 deg C.
Christchurch and Ashburton can expect some similar warming over the next few hours, but that will cool off soon.
Additionally, O'Connor said there were some weather watches around the country.
Stronger winds will go through the Canterbury High Country but are expected to ease in the course of the day.
The heavy rain in Fiordland has passed.
There was a strong wind warning for Clutha, Southland and Stewart Island.
'A wave of warm air'
Alistair Davey, who runs Davey Gardens in Timaru, told Morning Report the high temperatures weren't normal so early in the day, but there was a light breeze now.
"I went outside at 6.30am and it was just a wave of warm air.
"It was quite unusual for this time in the morning, but prior to that about 3am, there was a bit of rain on the roof, which has obviously come from the northwest.
"Now it's quite cloudy, but it's still quite warm here."
He grows dahlias and daffodil balls.
The daffodil balls were not affected but the heat could cause some stress for the dahlias.
"They did forecast it was going to be quite warm on Saturday and Sunday, which it has been."
The past summer was a hot and dry one, with above average temperatures and below average rainfall for many parts of New Zealand.
The National Institute of Water and Atmospheric Research's (NIWA) summer climate summary showed it was the ninth warmest summer on record, with a nationwide average temperature of 17.6C.
The Mackenzie Basin at Lake Tekapo with 2658 hours of sunshine throughout 2023.
