But high temperatures were likely inland.
"Northwesterlies will come back around the middle of the month and heat things up.
"A low is also expected to come in from the Tasman Sea around mid-January which should bring a bit of rain to the West Coast of both islands that may spill over to Wairarapa."
Masterton has had fairly consistent maximum and median temperatures and rainfalls in January in the past five years, according to National Institute of Water and Atmospheric Research (Niwa) data.
Maximum temperatures peaked between 24.4C last January and 27.7C in January 2011, while mean temperatures were between 16.3C last January and 18.4C in January 2011.
Rainfall was highest in 2011, at 423.8mm for January and lowest in 2013, at 8.6mm.
Niwa's latest outlook predicts Wairarapa temperatures will be above average and rainfall to be near or above average from January to March.
Nationally there had been a far healthier mix of sun and rain so far this summer, compared to the previous four or five summers, Mr Duncan said.
"When the farmers are happy, the townies usually aren't and when the townies are happy, the farmers usually aren't, but this summer has probably got the closest you get to having both sides happy," he said.
"It's hard to explain to people that's it's good to get one or two days of rain in the middle of your summer holidays but the thing is, it's good for the economy.
"A couple of days of rain will save you money at the supermarket."
The country would get "pockets of drought-like weather" but they would unlikely be consistent enough to be considered a drought, he said.
MetService meteorologist John Law said highs that had dominated New Zealand during the first week of this month were expected to continue next week, bringing more warm and drier-than-usual conditions to most of the country.
"Following that, some welcome rain is signalled mid-month, with warmer northerlies producing a wet week over New Zealand," he said.
Warmer conditions would return by the end of the month, taking overall January temperatures to above average.
Meanwhile, rainfall would be above normal for north-facing regions and normal to dry elsewhere, he said.
NZME.