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MetService forecaster Aidan Pyselman said on Saturday, Alexandra had a high of 31degC and Wanaka reached 29degC on Thursday, Friday and Saturday.
Yesterday, Dunedin recorded 29degC.
"For all three locations, it was their highest temperatures so far this year."
Not surprisingly, beaches around the Otago coastline and central lakes were very popular with local residents looking for some relief.
Mr Pyselman said the scorching weather was caused by an active weather system which came in from the Tasman Sea, bringing northwesterly winds over the Southern Alps.
"It causes a Foehn effect. When wind comes over the Southern Alps, a lot of the moisture gets dropped on the west side, the air compresses and when it comes down the other side it’s warmer, and if you get good sunshine on top of that as well, it helps to enhance it all."
Much of the southern region basked in the mid-20s until yesterday afternoon, when temperatures dropped sharply, due to a new set of troughs crossing over the South Island, he said.
"It’s going to be quite a drastic change this week.
"It’s looking like quite a cold week — going back to spring sort of weather.
"Temperatures will be in the mid to high teens and the first few days of the week will be quite showery."
The active series of troughs were forecast to move east across southern and central New Zealand tomorrow and on Wednesday, bringing likely warning amounts of rain to Fiordland and the Otago headwaters.
There is also a possibility of warning amounts of rain in Southland and Clutha on Wednesday and early Thursday; and northwest gales could become severe in Fiordland, Southland and Otago tomorrow, before turning southwest on Wednesday and easing on Thursday.
"Generally, it’s going to be more unsettled until this trough moves away later in the week," Mr Pyselman said.