Jamie Morton

Jamie Morton is science reporter at the NZ Herald.

Autumn weather: What to expect

Autumn is likely to be pretty settled, according to NIWA. Photo / Thinkstock
Autumn is likely to be pretty settled, according to NIWA. Photo / Thinkstock

Settled conditions that characterised last month's weather are expected to continue for the next three months, with a new long-range climate summary forecasting near normal rainfall, temperatures and soil conditions across New Zealand.

Temperatures between March and May would be mostly likely near average for all regions across the country, although as autumn progressed cold snaps and frosts could expected in some areas, according to a climate outlook released by the National Institute of Water and Atmosphere (NIWA).

March to May rainfall was likely to be near normal or below normal for the north and west of the North Island, and for the north, west and south of the South Island.

For the eastern regions of both Islands, three-month rainfall totals were most likely to be in the near normal range.

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Sea surface temperatures were expected to be near average for the coming three months, while soil moisture levels and river flows were most likely to be below normal in the north and west of the North Island and in the west and south of the South Island.

They were also about equally likely to be near normal or below normal in the north and east of the South Island, but most likely to be near normal in the east of the North Island.

Sea level pressures were expected to be lower than normal to the north of the country across the period, with higher pressures than normal to the southeast of New Zealand.

"This circulation pattern is likely to be associated with anomalous north-easterly flows over the North Island and anomalous weak easterly flows over the South Island," NIWA reported.

Sea surface temperatures were expected to be near average around New Zealand, for the coming three months as a whole.

The equatorial Pacific Ocean continued in a neutral ENSO-state - influenced by neither El Nino nor La Nina patterns - last month.

International guidance indicates that ENSO-neutral conditions were the most likely outcome for autumn, but in the following winter season about half the international models develop El Nino or borderline El Nino conditions.

Northland, Auckland and Waikato:

Temperatures are most likely (45% chance) to be in the near average range.
Rainfall totals are equally likely (40% chance) to be in the near normal or below normal range.
Soil moisture levels and river flows are most likely (55%) to be in the below normal range.

Central North Island, Taranaki, Wanganui, Manawatu, Wellington:

Temperatures are most likely (45% chance) to be in the near average range.
Rainfall totals are likely (40-45% chance) to be in the normal or below normal range.
Soil moisture levels and river flows are most likely (50%) to be in the below normal range.

Gisborne, Hawke's Bay, Wairarapa:

Temperatures are most likely (45% chance) to be in the near average range.
Rainfall totals, soil moisture levels and river flows are most likely (45-50% chance) to be in the near normal range.

Nelson, Marlborough, Buller:

Probabilities are assigned in three categories: above average, near average, and below average.
Temperatures are most likely (45% chance) to be in the near average range.
Rainfall totals, soil moisture levels and river flows are all equally likely (40% chance) to be in their near normal or below normal ranges.

West Coast, Alps and foothills, inland Otago, Southland:

Temperatures are most likely (45% chance) to be in the near average range.
Rainfall totals are equally likely (40% chance) to be in the normal or below normal range.
Soil moisture levels and river flows are most likely (45% chance) to be in the below normal range.

Coastal Canterbury, east Otago:
Temperatures are most likely (50% chance) to be in the near average range.
Rainfall totals are most likely (50% chance) to be in the normal range.
Soil moisture levels and river flows are likely (40-45% chance) to be in the below normal or near normal range.

- NZ Herald

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