Niwa forecasting principal scientist Chris Brandolino said the atmospheric imprint of La Nina continued to be strong and the Southern Oscillation Index (one of the key atmospheric indices for gauging the strength of La Nina events) during April was tracking to become the third-highest April value on record since at least 1876.
"Around the country, sea surface temperatures ranged from 0.3degC to 2.7degC above average during April."
That meant between May and July, air pressure was forecast to be higher than normal to the east and lower than normal to the northwest of the country, causing more easterly quarter winds than normal and a continued reduction in westerly quarter winds.
On the West Coast, along the Southern Alps and foothills, in inland Otago, and Southland, temperatures were very likely to be above average, Mr Brandolino said.
"Marine heatwave conditions will likely delay the seasonal transition to cooler temperatures, frosts and the potential for snowfall."
Rainfall totals were most likely to be near normal, although seasonal rainfall patterns might continue to be irregular with longer dry spells interspersed with heavy rainfall events, he said.
Soil moisture levels and river flows were equally likely to be near normal or below normal.
In coastal Otago, temperatures were about equally likely to be above average or near average; rainfall was about equally likely to be near normal or below normal; and soil moisture levels and river flows were most likely to be near normal, he said.
