An atmospheric river is expected to bring a month’s worth of rain to many parts of New Zealand for the start of May.
Niwa National Climate Centre forecasting principal scientist Chris Brandolino said over the next week or so, a northerly-quarter airflow was expected to bring tropical moisture and very warm temperatures towards New Zealand, resulting in widespread, heavy rainfall and an increased risk of flooding.
"A period of northerly winds in early May looks to deliver heavy rainfall to northern parts of this region, with large parts of Otago and Southland likely missing the heaviest of the rain."
During the rest of May, Enso-neutral conditions (neither El Nino or La Nina) were expected to bring "variable" weather patterns resulting in mixed air flows, with a tendency towards more frequent southerly flows at the onset of winter.
He said continually warming seas across the equatorial Pacific meant Enso-neutral conditions would turn to El Nino weather conditions during winter.
Despite the threat of heavy rainfall over the next week, the coming three-month period (May-July) would have below normal or near normal rainfall totals, and near normal soil moisture levels and river flows across the east of the South Island.
Temperatures were about equally likely to be above average or near average, he said.
On the West Coast, the Southern Alps and foothills, inland Otago, and Southland, temperatures were most likely to be above average, rainfall totals were about equally likely to be normal or above normal, but soil moisture levels and river flows were about equally likely to be near normal or below normal for the next three months.
