Outlook Summary

• Rainfall is about equally likely to be below normal or near normal in all regions of Aotearoa New Zealand except the north of the North Island, where near normal rainfall is most likely. It’s possible that long dry spells continue over the next three months.
• While rainfall events will occur over the next three months, their frequency may be reduced compared to normal. Groundwater and dam level recharge and increases in river flow and soil moisture will likely be less pronounced than normal.
• Temperatures are very unlikely to be colder than average for the three months as a whole. Above average or near average temperatures are favoured for all regions except the east of the South Island, where above average temperatures are most likely.
• While frosts and cold spells will occur occasionally, they are generally expected to be brief.
• Air pressure is predicted to be higher than normal to the east of the country. This is expected to be associated with more westerly and northeasterly quarter winds than normal.
• La Niña transitioned to ENSO neutral conditions in the equatorial Pacific Ocean during April as the sub-surface ocean continued to warm. For more information, see the Background.
• Coastal sea surface temperatures (SSTs) ranged from 0.6 to 1.3˚C above average during April. Many areas experienced marine heatwave conditions, as described in the Background.
• Soil moisture levels and river flows are most likely to be near normal in the north and west of the North Island, below normal in the east of the South Island, and about equally likely to be near normal or below normal in all other regions.

Regional predictions for May – July 2021

Northland, Auckland, Waikato, Bay of Plenty

The table below shows the probabilities (or percent chances) for each of three categories: above average, near average, and below average. In the absence of any forecast guidance there would be an equal likelihood (33% chance) of the outcome being in any one of the three categories. Forecast information from local and global guidance models is used to indicate the deviation from equal chance expected for the coming three-month period, with the following outcomes the most likely (but not certain) for this region:

• Temperatures are about equally likely to be above average (50% chance) or near average (45% chance).
• Rainfall totals are about most likely to be near normal (45% chance).
• Soil moisture levels and river flows are most likely to be near normal (45% chance).

The full probability breakdown is:

Central North Island, Taranaki, Whanganui, Manawatu, Wellington

Probabilities are assigned in three categories: above average, near average, and below average.

• Temperatures are about equally likely to be above average (50% chance) or near average (45% chance).
• Rainfall totals are about equally likely to be below normal (40% chance) or near normal (35% chance).
• Soil moisture levels and river flows are most likely to be near normal (45-50% chance).

The full probability breakdown is:

Gisborne, Hawke’s Bay, Wairarapa

Probabilities are assigned in three categories: above average, near average, and below average.

• Temperatures are about equally likely to be above average (50% chance) or near average (45% chance).
• Rainfall totals are about equally likely to be near normal (40% chance) or below normal (35% chance).
• Soil moisture levels and river flows are equally likely to be near normal (40% chance) or below normal (40% chance).
• River flows will likely be slow to recover since there is a lag between soil moisture replenishment and an increase in river flows.
• Meteorological drought re-emerged during April in northern Hawke’s Bay and coastal Gisborne according to NIWA’s New Zealand Drought Index.

The full probability breakdown is:

Tasman, Nelson, Marlborough, Buller

Probabilities are assigned in three categories: above average, near average, and below average.

• Temperatures are equally likely to be above average (45% chance) or near average (45% chance).
• Rainfall totals are about equally likely to be below normal (45% chance) or near normal (40% chance).
• Soil moisture levels and river flows are about equally likely to be near normal (40-45% chance) or below normal (40% chance).

The full probability breakdown is:

West Coast, Alps and foothills, inland Otago, Southland

Probabilities are assigned in three categories: above average, near average, and below average.

• Temperatures are equally likely to be above average (45% chance) or near average (45% chance).
• Rainfall totals are about equally likely to be near normal (45% chance) or below normal (40% chance).
• Rainfall deficiencies will continue to be possible in the hydro lake areas.
• Soil moisture levels and river flows are equally likely to be below normal (40% chance) or near normal (40% chance).

The full probability breakdown is:

Coastal Canterbury, east Otago

Probabilities are assigned in three categories: above average, near average, and below average.

• Temperatures are most likely to be above average (50% chance).
• Rainfall totals are about equally likely to be below normal (45% chance) or near normal (40% chance).
• Soil moisture levels and river flows are most likely to be below normal (50-55% chance).
• With the end of growing season, there will be less soil water uptake by plants, meaning that soil moisture can recover during rainfall events.
• River flows will likely be slow to recover since there is a lag between soil moisture replenishment and an increase in river flows.

The full probability breakdown is:

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