New Zealand's hot, dry summer looks set to continue, with the La Niña weather pattern, warm seas and high pressure systems combining to keep temperatures up.
NIWA's latest climate outlook, for January to March, predicts plenty of heat.
Its principal scientist, Chris Brandolino, said the higher temperatures and humidity could mean more restless nights for some.
"It's going to make for some tough sleeping nights - probably more than usual."
Rainfall over the three-month outlook period was predicted to be about average, although rather than persistent falls NIWA expected long, dry periods to be interrupted by sodden patches.
"These extended dry periods are likely to persist," said Brandolino.
Eastern areas of the North and South islands may find some respite, thanks to onshore winds.
It originally appeared as if Northland, Waikato, Southland and Otago would be New Zealand's driest areas this summer, Brandolino added, but a lack of rain elsewhere meant a greater proportion of the country was now in for a parched summer.