Christchurch is officially in a heatwave.
Temperatures reached 24 deg C in the city on Tuesday afternoon.
MetService said a heatwave must have five days of temperatures more than 5 deg C above the average.
Forecaster Tahlia Crabtree said the forecast for 25 deg C would just nudge the city into heatwave territory.
She says dry northwest winds have pushed temperatures above the 19 deg C average.
Crabtree said the past four days have all met the criteria with yesterday peaking at 27 deg C.
She said Auckland and Wellington are sitting on average weather.
"The last four days have all met that criteria, yesterday it got to 27 at the peak of the day in Christchurch so we are keeping a close eye on what's going to happen today."
