Niwa forecasting principal scientist Chris Brandolino said a La Nina watch remained in effect, and there was just over 50% chance that the La Nina weather phenomenon would officially develop by the end of this year.
"However, this event is likely to be weak and short-lived, and might stay below traditional La Nina thresholds."
He said there were indications for more widespread dry conditions than what was typical for La Nina across much of New Zealand, especially during November.
"Chances for more anticyclonic conditions over, and to the southeast of New Zealand, may lead to dry spells developing, especially in the west of both islands.
"La Nina-like conditions could, on the other hand, bring short and intense rain events for the north of the North Island and the eastern parts of both islands."
On the West Coast, Southern Alps and foothills, inland Otago and Southland, temperatures were "very likely" to be above average, he said.
"More northeasterly winds may contribute to more days above 25°C than normal."
Rainfall totals, soil moisture levels and river flows were about equally likely to be below normal or near normal.
"Consistent with La Nina-like conditions, northeasterly quarter flow anomalies may cause extended dry spells during the three-month period."
In coastal Otago, temperatures were also "very likely" to be above average, with northeasterly quarter wind anomalies possibly leading to "warmer nights, but cooler days".
Rainfall totals are about equally likely to be near normal or below normal, he said.
"While the prevalence of high pressure over New Zealand could lead to extended dry periods, bouts of northeasterly winds could bring infrequent short and sharp rain events for the region."
Soil moisture levels and river flows were most likely to be near normal.
Mr Brandolino said marine heatwave conditions were now occurring near the southeast of the North Island and east of the South Island, and to a lesser extent, along the west coast of the North Island.
There were suggestions marine heatwave conditions may intensify in the months ahead, he said.
