Southland's soils are starting to lean drier than usual for the first time in months, according to weather forecaster Philip Duncan, as a very strong El Niño begins to make its presence felt.
Writing in Farmers Weekly on 25 October, Mr Duncan said late October was when El Niño's effects usually became clearer, and although they had been slow to build, "we are now certainly seeing a drying-out phase expanding quite quickly across numerous regions".
Southland, especially around Invercargill and the plains, was among the regions starting to dry, alongside Waikato, Bay of Plenty, Tararua, Manawatū and Nelson. The driest soils in the country were in Northland, coastal Bay of Plenty and from East Cape to Gisborne, where rainfall deficits had reached 30 to 50 millimetres.
The picture is different just to the north. Canterbury, Marlborough and northern and coastal Otago were leaning wetter than usual, with soil moisture surpluses of 20 to 60 millimetres after low-pressure systems pushed rain over the Southern Alps.
Any drying will be welcome on many Southland farms. Environment Southland recorded the region's wettest winter since 1980, with 33 per cent more rain than normal, and a medium-scale adverse event was declared for Southland and Clutha at the start of October after a cold, wet spell left farmers with little or no grass growth.
The seasonal outlook from Earth Sciences New Zealand, the agency formed from NIWA and GNS Science, does not yet point to a dry summer in the south. Its October to December outlook, issued on 1 October, said very strong El Niño conditions were present in the tropical Pacific and were expected to strengthen further, with the event likely to peak in late spring or early summer and possibly rank among the strongest on record.
For the region covering the West Coast, the Southern Alps, inland Otago and Southland, the outlook gave rainfall a 55 per cent chance of being above normal, with an increased potential for heavy rain events and unusually strong winds. Soil moisture and river flows were most likely to be near normal, at 45 per cent, and temperatures were about equally likely to be near or above average.
El Niño typically dries eastern New Zealand first because of frequent westerly winds, Mr Duncan said, but this year high-pressure systems crossing the top of the country had dried the north first. He described the slow-moving high that dominated the past week as "humongous" in meteorological terms.
The short-term outlook is for a cold snap before the next high arrives. Mr Duncan said a significant cold change would move up the South Island on Wednesday, with colder air possibly lingering over the lower South Island until Saturday, followed by another large anticyclone over the weekend.
MetService has issued a road snowfall warning for the Milford Road from midnight tonight until 5am on Friday, with up to 1 centimetre possible above 700 metres, the Otago Daily Times reported. Invercargill is forecast to reach only 10 to 12 degrees on Friday.
Earth Sciences New Zealand's November to January outlook is due in early November.
