"Drought is insidious - it is a long-term thing," Griffiths said. "You can get a couple of sprinkles with fronts going through, but it sneaks up and it's been five months sneaking up already - so it is a concern," she said.
Federated Farmers president William Rolleston said the federation was advising farmers to re-do their feed budgets and to make early decisions.
"With good forecasting, farmers have been able to make good decisions earlier than they have been able to in the past," Rolleston said.
"There is no sign that the weather pattern is going to change at this point, so farmers do need to be making those decisions."
ANZ rural economist Con Williams said cold and windy weather on the east coasts of both islands may have made pasture cover shorter than many farmers would like.
"The fear is that it will go hot and dry pretty quickly, which would mean that there would not be a bank of feed there." Williams said it was too early to start crying drought. "It's more of a fear at the moment, as opposed to what has actually occurred," he said.
Many farmers are still suffering the after-effects of the 2012/13 drought.
Beef and Lamb New Zealand's latest lamb crop survey shows only a modest improvement in numbers tailed this spring. At an estimated 25.8 million lambs, the figure was up 1.2 per cent on the previous spring, which was the second smallest lamb crop in nearly 60 years.
Griffiths said Nelson and Blenheim experienced their fourth driest spring on record, in observations starting in 1941. Nelson recorded 99mm of spring rainfall, only 39 per cent of normal, while Blenheim received 82mm, 44 per cent of normal.
Significant soil moisture deficits are now evident in Nelson, Marlborough, Canterbury and Central Otago, reflecting the high wind-run and low rainfall recorded over the last four months, she said.
The Southern Oscillation Index, a measure of pressure between Tahiti and Darwin, dipped to minus 1, strongly indicating an El Nino weather pattern.
Griffiths said global climate models showed a 70 per cent chance of the borderline El Nino continuing or possibly developing into a full El Nino by January.
In spring and summer during El Nino, there was a higher chance of below normal rainfall for the north and east South Island, as well as for the eastern North Island.
MetService has issued a drier than normal December outlook for many regions, including the east coast of both islands.
Drying out
•Soils are already extremely dry in the north and east South Island, and drying out fast in the eastern North Island.
•An extremely dry spring for the northeast South Island, following a very dry August.
•Nelson and Blenheim experienced their fourth driest spring on record.
•Significant soil moisture deficits are now evident in Nelson, Marlborough, Canterbury and Central Otago.
