Seasonal Climate Outlook - La Niña over, and a mild start to winter for New Zealand

Neutral conditions prevail in the tropical Pacific (no La Niña or El Niño), after the end of the 2011/12 La Niña event. Near New Zealand, lower than normal pressures are expected to the north of the country, with higher than normal pressures over southern New Zealand.

The NIWA National Climate Centre’s outlook for early winter, May to July 2012, indicates air temperatures are likely to be average or above average over most of the country, except for near average in the east of the South Island. Seas around New Zealand are likely to remain near normal or slightly cooler than normal during early winter.

Early winter rainfall is likely to be normal or above normal in the north and east of the North Island, and near normal in other regions. Similarly, soil moisture levels are likely to be normal or above normal in the north and east of the North Island and near normal in other regions. However, river flows are likely to be normal or above normal in the north and east of the North Island, normal or below normal in the west of both islands, and near normal in the north and east of the South Island.

Overall picture

Temperature

Seasonal temperatures are likely to be average or above average over most of the country, except for near average in the east of the South Island. Despite the overall pattern of near or above average temperatures, frosts typical of winter will occur from time to time.

Rainfall, soil moisture and river flows

Early winter rainfall is likely to be normal or above normal in the north and east of the North Island, and near normal in other regions. Soil moisture levels are likely to be normal or above normal in the north and east of the North Island and near normal in other regions. River flows are likely to be normal or above normal in the north and east of the North Island, normal or below normal in the west of both islands, and near normal in the north and east of the South Island.. 

Northland, Auckland, Waikato, Bay of PlentyRegional predictions for the next three months

Early winter temperatures are equally likely to be near average or above average. Seasonal rainfall totals, soil moisture levels, and river flows are all equally likely to be in the near normal or above normal range.

Probabilities are assigned in three categories: above average, near average, and below average. The full probability breakdown is:

 
Central North Island, Taranaki, Wanganui, Manawatu, Wellington

Seasonal temperatures are equally likely to be near average or above average. Early winter rainfall totals and soil moisture levels are likely to be near normal for the three month season as a whole, while river flows are likely to be near normal or below normal.

Probabilities are assigned in three categories: above average, near average, and below average. The full probability breakdown is:

 

Gisborne, Hawke’s Bay, Wairarapa

Seasonal temperatures are equally likely to be in the near average or above average range.   Early winter rainfall totals, soil moisture levels and river flows are all equally likely to be in the near normal or above normal range.  

Probabilities are assigned in three categories: above average, near average, and below average. The full probability breakdown is:

 

Nelson, Marlborough, Buller

Early winter temperatures are equally likely to be near average or above average. Seasonal rainfall totals, river flows, and soil moisture levels are all likely to be in the normal range.

Probabilities are assigned in three categories: above average, near average, and below average. The full probability breakdown is:

 

West Coast, Alps and foothills, inland Otago, Southland

Early winter temperatures are equally likely to be near average or above average. Seasonal rainfall totals and soil moisture levels are likely to be in the near normal range, while river flows are equally likely to be in the near normal or below normal range.

Probabilities are assigned in three categories: above average, near average, and below average. The full probability breakdown is:

 

 

 

Coastal Canterbury, east Otago

Seasonal temperatures are likely to be near average. Early winter rainfall totals, river flows, and soil moisture levels are likely to be in the normal range.

Probabilities are assigned in three categories: above average, near average, and below average. The full probability breakdown is:

Background

The 2011/12 La Niña event ended during April, and present conditions in the tropical Pacific are ENSO-neutral (no La Niña or El Niño). The three-month average of the Southern Oscillation Index (SOI) for February-April is close to zero. Sea surface temperatures are now warmer than normal in the eastern tropical Pacific.

Almost all global climate models predict neutral conditions in the tropical Pacific over early winter (May-July), with about half of them continuing this situation over the subsequent three months. However, about half the models predict the evolution of an El Niño state during the August-October period.  NIWA will continue to monitor the global climate situation. 

In spite of the collapse of La Niña in the tropical Pacific, the easterly circulation regime that has been dominating New Zealand climate patterns since December 2011 is expected to persist through the May to July 2012 period.