Niwa National Climate Centre principal scientist Chris Brandolino said the El Nino weather pattern near the International Dateline was forecast to continue during the next three months, which meant air pressure was expected to be higher than normal to the west and north of New Zealand and lower than normal to the south, resulting in more westerly quarter winds than normal.
Mr Brandolino said the weather in early June was expected to be unsettled and colder than average for most of New Zealand.
"But warmer-than-average coastal and Tasman Sea surface temperatures, along with a lack of southerlies, may reduce the risk for cold snaps.
"July could turn out to be a more settled month than June with an increased chance for high-pressure systems to affect New Zealand."
He predicted temperatures in inland Otago and Southland were equally likely to be above average or near average; and in coastal Otago they were most likely to be above average.
"Despite a low chance for a winter season with below-average temperatures, cold snaps and frosts remain likely to occur," he said.
Rainfall totals, soil moisture levels and river flows were about equally likely to be near normal or above normal in inland Otago and Southland.
But in coastal Otago, rainfall totals were most likely to be near normal, and soil moisture levels and river flows were likely to be below normal, he said.
"Influenced by El Nino, enhanced westerly wind flows may promote heavy rainfall events for the west of the South Island, especially since regional sea surface temperatures remain above average."
