Heavy rain is expected to hit the South Island today.
Niwa meteorologist Ben Noll said La Nina conditions peaked in the equatorial Pacific during January, and there was a 75% chance of it continuing for three months (February-April).
He said marine heatwave conditions would continue to have an "upward influence" on air temperatures and humidity, before easing during autumn.
In Southland, inland Otago and the West Coast, temperatures were very likely to be above average, and more frequent offshore winds might increase the frequency of hot days along the West Coast.
Rainfall totals were equally likely to be near normal or above normal, but heavy rainfall events, such as at the end of this week, could bring flooding, he said.
"However, periods of high pressure may also cause extended dry spells.
"In late January, very dry conditions were occurring in central and southern Otago, eastern Southland, and Stewart Island according to Niwa’s New Zealand Drought Index."
Soil moisture levels and river flows were most likely to be near normal, he said.
In coastal Otago, temperatures were equally likely to be above average or near average, and due to the marine heatwave conditions, periods of high humidity and warm overnight temperatures were likely.
However, he said a reduction in westerly winds may lead to fewer hot days than normal.
"Rainfall totals are about equally likely to be near normal or above normal. Predominant onshore winds may influence more cloud cover and drizzle.
"Soil moisture levels and river flows are most likely to be near normal."
Mr Noll said high pressure and drier weather may return during the second half of February, but there was another risk of heavy rainfall in March.
"There is an elevated risk for atmospheric river and ex-tropical cyclone activity around New Zealand in the coming months.
"These systems can bring heavy rainfall and increase the risk for flooding. Weather-sensitive groups should keep a close eye on day-to-day forecasts," he said.
