Niwa National Climate Centre principal scientist Chris Brandolino said coastal Otago temperatures were very likely to be above average, and periods of “unseasonable warmth” were possible due to more northwesterly winds in the area.
He said rainfall totals were equally likely to be near normal or below normal, but extended dry spells, which were unusual for this time of year, were likely.
Over the next three months, soil moisture levels were most likely to be near normal, and river flows were about equally likely to be near normal or below normal.
In Southland, inland Otago and the West Coast, temperatures were also very likely to be above average, he said.
Rainfall totals were most likely to be near normal, but more westerly wind flows during September could bring frequent fronts to the region, elevating the potential for heavy rainfall.
Soil moisture levels and river flows were about equally likely to be near normal or above normal.
“The trend of warmer-than-average temperatures is very likely to continue during spring.
“Unseasonably warm conditions will occur at times, particularly in the east of both islands.
“Despite this, cold spells and frosts can still occur occasionally, especially early in the season.”
Mr Brandolino said air pressure was expected to be higher than normal over and to the east of New Zealand, and these frequent high pressure systems might contribute to lengthy dry spells for this time of year.
He said New Zealand’s coastal sea surface temperatures ranged from 0.6degC to 1.1degC above average during August, and were predicted to become more unusually warm by November.
“Niwa continues in La Nina watch, acknowledging ocean and atmosphere conditions in the Pacific Ocean are trending toward La Nina for the second consecutive year.”
