He said Whanganui also had a record-breaking overnight temperature on Thursday, reaching the warmest minimum of 16.4C.
This was 2.6C higher than the previous record of 13.8C set in 2015.
It was warmer than Auckland and Hamilton, which also experienced record-breaking overnight temperatures, Auckland recording 16.1C on Thursday night.
Glassey said the high temperatures were strange for this time of year, but they were becoming more frequent.
"The other unusual thing was Thursday wasn't even a sunny day in Whanganui. It was cloudy with some rain at times."
Glassey said if there were clear skies there would have been more heat from the sun, and that would have made it even warmer.
The northerly wind direction was important, he said.
"There's something called the foehn effect, which warms temperatures on the sheltered side of the mountains more than usual.
"The moisture in the air rains out in the mountain and as that air comes down the other side of the ranges, there's less moisture in it so it has the ability to get warmer."
He said that combined with the warm moist air coming down from the tropics were contributors to the unique weather.
"It is very unusual to get this tropic air at this time of year, but even in summer it usually wouldn't last as long as this."
Glassey said the tropical air mass has been over the country since about Tuesday.
July also had record-breaking temperatures for Whanganui, with the Whanganui Airport temperature gauge recording 21.1C on July 8.
The airport weather station also recorded gusts up to 80km/h on Thursday about 9 pm.
"Because it's a northerly, Whanganui has a bit of sheltering from the heavy rain that's been hammering other parts of the country," he said.
Over the past 24 hours, the Whanganui Airport weather station recorded 6.8mm of rain.
Glassey said scattered rain was to be expected throughout the weekend, but not in huge amounts.
