But don't put the warm coat and brolly away yet - it doesn't mean there won't be cold, wet snaps.
A Niwa spokesman said temperatures were most likely to be"near average'', but rainfall totals were forecast to be in the"near normal or below normal'' range.
Soil moisture levels were also likely to be"below normal or near normal'' and river flows were most likely to be in the"below normal'' range, the spokesman said.
Niwa statistics show the mean temperature for Queenstown and Alexandra from May to July is 4.7degC.
Mean rainfall is 63.4mm for Queenstown and 27.7mm for Alexandra.
Coastal Otago temperatures and rainfall totals are most likely to be in the near-normal range, and soil moisture levels and river flows are likely to be in the above normal or near normal range, he said.
The mean temperature for Dunedin between May and July is 7.7degC, and the mean rainfall is 59.9mm.
``As we transition towards winter, frosts and cold snaps will occur from time to time in cooler locations, even in regions where elevated chance for higher than normal seasonal temperatures is forecast.''
He said international guidance and warmer sea temperatures in the eastern Pacific indicated a likely transition towards El Nino conditions over the three months of May to July.
``The models indicate increasing chance for El Nino becoming established later during the winter, with nearly 70% chance for the August to October period.
``For May to July as a whole, the atmospheric circulation around New Zealand is forecast to favour slightly more southwesterly flows than normal, but variable circulation regimes are to be expected over the course of the season.''
He said ocean waters surrounding New Zealand were warmer than average all around the country at present.
There were anomalies exceeding +1degC along the west coast of the South Island and close to +1degC along the north and east of the North Island.
``Sea surface temperatures [SST] remain warmer than average in the southern part of the Tasman Sea and along southeast Australia.
``The dynamical models' forecasts for SST indicate this pattern is likely to persist over the next three months and waters in the south Tasman Sea are expected to warm further.
``For May to July 2017 as a whole, coastal waters around New Zealand are thus forecast to be average or above average.''
An updated long-term forecast is expected to be released by Niwa in early June.
