He said this is probably to do with high levels flowing from the Waimakariri River due to heavy rainfall in the last week.
The cooler weather is not expected to last long with MetService predicting temperatures in the city will reach 21C on Friday and 26C on Saturday.
It follows a gloomy summer so far in Christchurch.
"People would have felt these long stretches of below-average temperatures," a MetService meteorologist said.
The only city that has had fewer sunshine hours than Christchurch so far this year is Invercargill.
Christchurch has had 125.7 hours as of January 19, compared to New Plymouth's 198 hours.