MetService meteorologist Georgina Griffiths, of Auckland, says Dunedin and Otago, and much of the rest of the country, have already experienced "extremely volatile" weather throughout much of the year.
This included the extreme weather event that brought record rainfall to Mosgiel, Oamaru and several other areas on July 21, as well as flooding on the Taieri Plain.
Throughout the year different parts of the country, including the North Island, had been hit by such extreme "rubbish" weather events, and she joked that some weather systems had seemed "on steroids".
Dunedin and several other places in Otago were highly likely to exceed their usual annual rainfall totals before the end of the year.
But when summer arrived, it could well bring more settled weather to the country and the southern annular mode — or "Sam" — could act as an important helping hand, Mrs Griffiths said.
The Sam is a ring of climate variability that encircles the South Pole and extends out to the latitudes of New Zealand, and involves alternating changes in windiness and storm activity.
Dunedin was likely to face some unsettled weather this month but there were early signs that Sam could be in a positive mode during December and early next year, bringing higher pressures to Dunedin and Otago and more settled, possibly warmer weather. Previously flooded soils could have a chance to start to dry out.
"We’re going to be looking forward to seeing a few more highs on the weather map."
Asked what could be expected from the El Nino-southern oscillation climate pattern, Mrs Griffiths said El Nino could be a weak influence. Early signs were it might not be influential this summer.
Sam was "one of the biggest drivers of southern hemisphere climate variability", she said.
"Annular" meant "ring-like", and Sam controlled the "ring of southern winds that circle the South Pole". Sam altered the north-south movement of the westerly wind belt around the Antarctic. In turn this changed westerlies’ strength over New Zealand, "rather like dominoes".
Sam was not well known in New Zealand but was "like worker bees" and was one of the mechanisms that played a key part in generating the country’s weather, "one of the biggest drivers of southern hemisphere climate variability", she said.
