She said the unusual heat was as a result of a strong northwesterly wind which increased temperatures across the eastern regions.
"There was some unusually high days even for January," she said.
"This occurred primarily because of a strong northwesterly wind which affected temperatures in Wairarapa on the 5th, 7th, 10th, 30th and 31st of January."
Graham Adam, of Solway, a former Eketahuna mayor, has been collating statistics since the 1980s when he bought a weather station.
He bought another automated weather station recently and set it up in his back garden.
He said the MetService figures and his own readings compared closely. Mr Adam recorded 35.7C on his station on Thursday and believed his reading was accurate.
"Whether being closer to buildings here has any effect or not there is lots of air and space at the back of my garden so it's still out in the open. When I saw 35.7 I thought it was exceptional."
The MetService said it was "entirely possible" that Mr Adam's reading was accurate as temperatures varied and fluctuated regularly depending on a range of environmental and physical factors such as a weather station's proximity to buildings.
Mr Adam said the summer heatwave had reminded him of his youth. "It's like we used to have summer, this is what I remember years ago."
He said from 1949 to 1963 regular heatwaves adversely affected farming in the region. "Some of the old farmers farming in the region in those days, after Christmas their cattle went away to the good country, there was no grass, no feed because we had a drought and this sort of summer year after year."
Niwa said temperatures in Masterton had been significantly higher than usual for January with an average mean temperature of 19.7C.
The heatwave has led to major concerns for farmers as feed is low and they are being forced to sell off stock.
