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Otago could experience an "up and down" weather pattern as it heads into autumn, MetService's seasonal outlook through to May predicts.
A weakening La Nina signal might result in an increased variability in the country's weather, MetService consultant meteorologist Ross Marsden said.
Over the next few months, anticyclones were likely to shift their track from the central Tasman Sea to the northern Tasman Sea.
"They should still bring some periods with light winds and settled weather, good for harvesting, but these are likely to become fewer and weaker."
Cold fronts and associated troughs of low pressure were expected to move on to southern districts from the Tasman Sea, bringing occasional rain.
Some might form a low pressure area, either to the south of Southland, or to the south of Chatham Islands, producing a cold southerly flow on to eastern districts of the South Island.
During autumn any low pressure systems that developed in the Tasman Sea might bring moist winds from the tropics southwards to clash with cold air fresh from the polar regions, Mr Marsden said.
"This clash of ingredients may lead to sudden and explosive thunderstorms with possible downpours, lightning, hail and gusty winds."
In Coastal Otago, passing cold fronts were expected to bring showery weather with coastal gales, which could occasionally be cool enough to bring snow to the mountains. Between the fronts there should be a day or so of settled weather.
This "up and down" weather should be the main pattern for the rest of autumn and into winter, he said.
Cold fronts with southwest wind changes were expected to bring small and rather scattered amounts of rain.