Rotorua had the warmest summer since 1964 and temperatures aren't about to drop dramatically come autumn, Niwa says.
The mean temperature was 19.1C. February 13 was the warmest summer night since records began in 1972 at 20.8C.
The minimum average temperature was 14.5C which was also a record breaker, the warmest summer minimum average since records began, Niwa's Chris Brandolino said.
"So what that communicates is the nights were warm, the mornings were warm and that goes hand in hand with that was the warmest summer on record in Rotorua since 1964," Brandolino said.
It wasn't only warm, it was also a wet summer.
"Rotorua had 436.2mm of rainfall this summer. Typically you receive 304.1mm so it's 143 per cent of normal - we call that above normal rainfall," Brandolino said.
The first 15 days of February were the wettest, when 199.4mm rainfall occured. Brandolino said this was "pretty impressive".
Rotorua also had its fourth highest summer wind gust since 1972 - 91km/h on January 5.
Niwa released its regional predictions for March to May this week, which said it was likely to be warmer than usual in the Bay of Plenty, with rainfall totals likely to be in the normal range.
With La Niña's influence waning over the three-month period, New Zealand's regional climate is expected to be driven by warmer than average ocean waters around the country, in the Tasman Sea, and in the Southwest Pacific Ocean, which will influence surface air temperatures and the likelihood of significant rainfall events, the release said.
"I think the message for autumn is that we feel with high confidence that it's going to be a wetter than usual autumn. Doesn't mean there won't be cold snaps - even good marriages have bad days - it just means that it won't be the defining theme for autumn," Brandolino said.
He said summer-type weather may linger for longer than usual, but Niwa thought rainfall will be above normal, so wet and warm is probably the executive summary.
Meanwhile, this weekend in Rotorua will be fairly cloudy, but reasonably warm with a small chance of a shower.
MetService meteorologist Tom Adams said that was the situation for much of the country.
"In a town like Rotorua there will be some suburbs that do get rain, and there will be some that don't," he said.
"The showers will be pretty isolated on Saturday, more frequent by Sunday evening with wind from the northeast, which from Rotorua tends to bring the cloud in and traps the sulphur smell in town," Adams said.
"But it's not a bad weekend, fairly cloudy and temperature-wise things are pretty warm at the moment."
Regional predictions for the March–May 2018 season
Northland, Auckland, Waikato, Bay of Plenty
•Temperatures are very likely to be above average (70 per cent chance).
•Rainfall totals are most likely to be in the above normal range (50 per cent chance).
•Soil moisture levels and river flows are most likely to be in the above normal range (50 to 55 per cent chance).