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The atmospheric imprint of La Nina remains strong over New Zealand, meaning temperatures are likely to be warmer than average over the next three months.
But Niwa has warned cold snaps and frosts will still occur, particularly in the southern regions.
Niwa National Climate Centre forecasting principal scientist Chris Brandolino said a predicted lack of southerly winds and warmer-than-average coastal seas would "buffer" the country from
long-duration cold and reduce the frequency and intensity of cold spells, meaning temperatures for the West Coast, the Alps and foothills, Otago and Southland would be above average.
However, seasonal rainfall patterns might be irregular, with longer dry spells interspersed with heavy rainfall events, he said.
"There is the potential for more frequent spring anticyclones near the South Island, which could contribute to more easterly air flows and dry spells."
Despite the irregular rainfall patterns, soil moisture levels and river flows were expected to be near normal.
He said La Nina conditions were most likely to continue during July-September, and there was a 60% chance they would continue during October-December as well.
"Should La Nina persist through or redevelop by summer 2022-23, the current event would qualify as a ‘triple-dip’."
Since 1900, triple-dip events had occurred in 1998-2000, 1983-85, 1973-75 and 1908-10, he said.