"When things get so dry, you really need more than the average rainfall to bring the soils up to normal."
He said temperatures would be above average for the outlook period, but would gradually feel more autumnal in the coming weeks.
"It will stay warmer, I think, but people will start to notice that the summer is finished."
Dr Mullan said the seasonal climate outlook tracked general tendencies, but could not predict individual weather patterns, which could only be predicted up to 10 days out.
"You can't use it to forecast whether you take your umbrella to work.
"But if you're making lots of decisions about water use - and I think this applies to farmers as well as energy companies - you can bias your decision to take into account the fact that it could be a bit drier than normal."
WeatherWatch head analyst Philip Duncan said seasonal outlooks had some relevance but were not accurate enough.
"For the general public, they probably mislead people more than anything because it's not a weather forecast, it's a climate prediction," he said.
"This summer is a good example; there was no talk of a big drought coming, and that's what we got."
Mr Duncan said the key thing to take from the latest seasonal outlook was that the weather would be "far more chaotic" without a driving El Nino or La Nina.
He said rain was likely to move up the country today and tomorrow, and more rainmakers were predicted over the next two weeks. But it would not be significant enough to ease the drought.
"For that, we need to have at least 100ml of rainfall in every part of the country. We aren't anywhere near that."
The dry conditions would ease slowly.
He said colder temperatures were likely from today and tomorrow.
"It's going to feel a lot like autumn. Temperatures are going to really drop, especially for the South Island."
But in the upper North Island, it would still feel like summer for much of April.
"We'll see cooler weather creeping in more and more in the next couple of weeks."
Winter sales some way off
Shoppers seeking winter clothing bargains could have to wait longer than usual this year, with the lingering warm weather delaying sales after a slow start to the season.
Retailers have reported poor sales of winter stock, according to this week's BNZ confidence survey, while even clothing giant Hallenstein Glasson has reported a 1 per cent drop in new season sales.
Retailers Association chief executive John Albertson said the warm weather had slowed the start to the season.
"Traditionally, particularly in the clothing and fashion sector, winter stock starts to come in throughout February, and those who are early adopters start buying in late February, early March.
"With the summer weather going right through to the end of March - and it's still looking pretty good out there - buying for winter is probably a long way from their thinking at the moment."
Mr Albertson said the slow start might make some stores reconsider the timing of their winter sales, which were usually held from late June or early July.
"Obviously they can't afford to head into a season doing everything at sale price."
