Fonterra last week revised down its production forecast for 2018/19 to 1,530 million kg of milksolids down from 1,550 million kg because of the dry weather.
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The co-op had been forecasting a 3 per increase over last year but it's looking more like a 2 per cent increase now.
The big dry follows what has been close to ideal growing conditions over most of 2018 and very early this year.
Dairy NZ said most parts of the country are currently affected by dry weather, with each region having its own hotspots.
"A few areas in both the North and South Islands had some rain recently, but most areas need a really good soaking coupled with follow-up rain to get soil moisture levels up to support grass growth," Dairy NZ's Vanessa Winning said.
"For most regions in New Zealand 70-130mm of rainfall is needed to fill the current soil moisture deficit," she said.
In the lower North Island, central Manawatu and Rangitikei are badly affected and farmers should take action now, if they haven't already.
The rest of the lower North Island is variable, with some dry pockets and others that have had good rain.
In the upper North Island all areas are affected, but to varying degrees.
Bay of Plenty and Central Plateau are very dry – and often are in summer.
North Waikato and some parts of Northland are drier than usual.
The top of the South Island is particularly affected by dry conditions, with drought declared in Tasman and support available to farmers from Dairy NZ, Federated Farmers, Rural Support Trust and others.
Other South Island areas particularly affected by the dry weather is the northern West Coast including Karamea, Westport, Reefton and parts of Grey Valley.
Southland and Canterbury are aided by irrigation, but irrigation restrictions are coming into effect, Winning said.
