A scorching Mother's Day is in store for Sunday, when the mercury could reach record May levels.
An unseasonably hot weekend is forecast for the South Island.
Christchurch is expected to reach a sweltering 25C. The previous record high for the city in May is 27.4C.
MetService meteorologist Lewis Ferris said the 22C predicted for Dunedin, Oamaru and Alexandra on Sunday was "unusually high" for this time of year — between 8.4C and 9.5C above average.
A large trough of low pressure is forecast to move east over New Zealand from the Tasman Sea on Saturday through to Tuesday, bringing strong northwesterlies and periods of heavy northerly rain to western parts of the South Island.
Fellow meteorologist Ashlee Parkes said most other areas would begin to cloud over and would experience rising humidity on Saturday.
"Some [areas] may experience a clammy night on Saturday thanks to the moist northwesterly flow," Parkes said.
"Temperatures on Sunday are also forecasted to push into the 20s across the eastern South Island due to this warming wind."
Kaikoura and Christchurch are expected to reach a high of 25C."
Parkes said scattered falls of rain would push their way across into the eastern South Island on Sunday, but they would be short-lived and not everyone would receive decent rainfall.
Much of Otago and Canterbury is now in drought.
Dunedin City recorded its equal driest April since records began in 1918 — just 12mm.
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