A low front was crossing central New Zealand from the west, which meant people in Taupo, Taranaki, Whanganui, Manawatu, Wellington and Wairarapa could expect the heavy downpours to continue through to mid-week.
MetService has issued a heavy rain warning for these regions.
In the Wairarapa especially, 80 to 120mm of rain was expected to accumulate by the end of the weekend.
MetService has forecast peak intensities in the region of 10 to 25mm an hour, and 25 to 40mm during thunderstorms.
"Heavy rain may cause streams and rivers to rise rapidly. Surface flooding and slips are also possible and driving conditions may be hazardous."
In Wellington, a strong wind watch had been issued as southerly gales may become severe in exposed places, MetService said.
Niwa Weather reported heavy cloud and rain was expected in Marlborough and northern Canterbury for much of tomorrow, along with a chance of thunder.
"On the plus side, this rainfall will be beneficial for regions enduring very dry soils," Niwa Weather said.
In Otago and Southland, some isolated showers were expected tomorrow but mainly it was likely to be fine, MetService said.
The chilliest spot in the country today was Tongariro , which dropped to 1.5C this morning. The Rangitikei region was close, falling to 2C.
The hottest part of the country was Kerikeri, which managed to reach 21.8C.
Best said overall the weather had been relatively normal for this time of year.
Some parts of the country had been slightly colder than previous years, such as Masterton, which was 7C below average and Christchurch, which was 5C below average.