Niwa National Climate Centre forecasting principal scientist Chris Brandolino said moderate La Nina conditions continued during September, a marine heatwave strengthened in New Zealand’s coastal waters, and both were expected to influence the climate in October, November and December.
"October may have variable temperatures before a more marked rise in November and December, along with an increase in humidity."
On the West Coast, in the Alps and foothills, in Southland and inland Otago, temperatures were "very likely" to be above average, he said.
"More northeasterly winds and marine heatwave conditions will cause increased sunshine and warmer temperatures.
"Rainfall totals are most likely to be below normal. More offshore winds will likely result in extended dry spells, and low rainfall may also occur around the hydro lakes.
"However, occasional heavy rainfall events may still occur, such as in the second week of October."
Soil moisture levels and river flows were about equally likely to be near normal or below normal.
Along coastal Otago, temperatures were also likely to be above average, but fewer northwesterly winds may mean fewer hot days, he said.
"Although, more frequent northeasterly winds may contribute to more cloud cover and warmer overnight temperatures."
Rainfall totals are about equally likely to be near normal or below normal.
"Frequent anticyclones may contribute to longer dry spells, although these may be interspersed with occasional sub-tropical lows that bring rain from the north.
"Soil moisture levels and river flows are about equally likely to be near normal or below normal."
Mr Brandolino said La Nina conditions were very likely to continue during October-December, making it the first "triple dip"(three consecutive La Nina events from 2020-22) since the 1998-00 triple dip.
However, the long-term outlook showed there was a 45%-50% chance the La Nina weather conditions will stop during January-March next year.
