Temperatures for Whanganui this month have been more than 5 degrees above average for May.
MetService meteorologist Andrew James said over the first week of the month, the average temperature in the region was 18C, significantly higher than the average mean temperature of 12.8C.
Temperatures have been so warm, even the average overnight low of 15 degrees is higher than the expected average.
James said this was due to a ridge of high-pressure air sticking over the east coast of the country.
“What that does is it drags down that warm air from the tropics and it also means weather systems can’t pass through,” he said.
This in turn led to weather systems to the north being sucked down over Aotearoa which resulted in the warm and wet conditions experienced over the start of the month.
However, James noted these balmy conditions did not mean the rest of the month would continue on this trend as the seasons transitioned.
“We’re only a week in and we’re also the warmest week in.
“If you think about as we go into winter, on average the end of May is quite a lot cooler than the start of May,” he said.
This coming week is expected to record a steep drop in temperature for the region.
The northerly flow will continue over the beginning of the week, bringing wet weather with it and an expected high of 23C on Tuesday and 19C on Wednesday.
However, by Thursday a low-pressure system will arrive over the region, which James said will break the dam and bring in a cold snap with a high of 13C and an overnight low of 5C.
“That’s a good 10C cooler than it’s been overnight these past few nights, people will definitely notice it feels a lot more wintery from about the middle of this week,” James said.
Thursday will be the coldest day of the week, with conditions from Friday onwards being cooler than last week but closer to the average expected for the month.