Whanganui has recorded its second warmest December day since records began in 1978.
Measured at Whanganui Airport, temperatures soared to 29.3C, just 0.4C lower than the highest ever.
MetService meteorologist Paul Ngamanu said the warm weather had a bit to do with where Whanganui was positioned.
"We've had this warm, humid air mass over the country for a few days and that is helping bring those temperatures up.