September - November 2011 Cool Start, Mild and Dry Later
The NIWA National Climate Centre's spring outlook for New Zealand, for September – November as a whole, indicates that temperatures are likely to be above average in the North Island as well as for the northern South Island, and near average or above average in other regions. Cool spells typical of spring will occur from time to time through the period, especially during September. Seasonal rainfall, soil moistures, and river flows are all likely to be normal or below normal for the North Island as well as the western South Island, and near normal in other regions.
The tropical Pacific is currently in the neutral range (neither La Niña nor El Niño), and is expected to remain neutral through the spring, according to the NIWA National Climate Centre.
The outlook states that mean sea level pressures are likely to be above normal across much of New Zealand, with weaker westerly circulation than normal over the country, for the season as a whole.
Overall Picture
Temperature:
For the September - November period as a whole, air temperatures are likely to be above average in the North Island as well as for the northern South Island, and near average or above average in other regions. Cool spells typical of spring will occur from time to time through the period, especially during September. Sea surface temperatures near New Zealand are expected to be close to normal or slightly below normal through the period.
Rainfall, soil moisture, and river flows:
The National Climate Centre says that spring rainfall is likely to be normal or below normal for all of the North Island as well as the west of the South Island, and near normal in other regions. Soil moisture levels and river flows are also likely to be normal or below normal in all of the North Island regions and the west of the South Island, and near normal in other regions.
Regional predictions for the next three months:
Northland, Auckland, Waikato, Bay of Plenty:
Temperatures are likely to be above average for the time of year. Spring rainfall totals are equally likely to be in the normal or below normal range, as are soil moisture levels and river flows.
Probabilities are assigned in three categories; above average, near average, and below average. The full probability breakdown is:
| Temperature | Rainfall | Soil moisture | River flows | |
| Above average | 50% | 20% | 20% | 20% |
| Near average | 30% | 40% | 40% | 40% |
| Below average | 20% | 40% | 40% | 40% |
Central North Island, Taranaki, Wanganui, Manawatu and Wellington:
Spring temperatures are likely to be above average. Rainfall totals, soil moisture levels and river flows for September – November as a whole are equally likely to be in the normal or below normal range.
Probabilities are assigned in three categories; above average, near average, and below average. The full probability breakdown is:
| Temperature | Rainfall | Soil moisture | River flows | |
| Above average | 50% | 20% | 20% | 15% |
| Near average | 30% | 40% | 40% | 45% |
| Below average | 20% | 40% | 40% | 40% |
Gisborne, Hawke's Bay, Wairarapa:
Temperatures are likely to be above average for the time of year. Spring rainfall totals are equally likely to be in the normal or below normal range, as are soil moisture levels and river flows.
Probabilities are assigned in three categories; above normal, near normal, and below normal. The full probability breakdown is:
| Temperature | Rainfall | Soil moisture | River flows | |
| Above average | 50% | 20% | 20% | 20% |
| Near average | 30% | 40% | 40% | 40% |
| Below average | 20% | 40% | 40% | 40% |
Nelson, Marlborough, Buller:
Temperatures over the September - November period are likely to be above average. Rainfall totals, soil moisture levels and river flows for spring as a whole 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:
| Temperature | Rainfall | Soil moisture | River flows | |
| Above average | 50% | 25% | 25% | 20% |
| Near average | 30% | 50% | 50% | 50% |
| Below average | 20% | 25% | 25% | 30% |
West Coast, Alps and Foothills, Inland Otago, Southland:
Temperatures over the September - November period are equally likely to be above average or near average. Rainfall totals for spring as a whole are equally likely to be in the normal or below normal range, as are soil moisture levels and river flows.
Probabilities are assigned in three categories; above average, near average, and below average. The full probability breakdown is:
| Temperature | Rainfall | Soil moisture | River flows | |
| Above average | 40% | 20% | 20% | 15% |
| Near average | 40% | 40% | 40% | 45% |
| Below average | 20% | 40% | 40% | 40% |
Coastal Canterbury, East Otago:
Spring temperatures are equally likely to be above average or near average. Rainfall totals, soil moisture levels and river flows for spring as a whole 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:
| Temperature | Rainfall | Soil moisture | River flows | |
| Above average | 40% | 25% | 20% | 20% |
| Near average | 40% | 50% | 50% | 45% |
| Below average | 20% | 25% | 30% | 35% |
Background
The tropical Pacific remains in an ENSO-neutral state, with most signs of the preceding La Niña event having dissipated. However, recent developments suggest a possible resurgence of La Niña conditions, at least temporarily. However, global models which predict ENSO (El Niño-Southern Oscillation) are all indicating ENSO-neutral conditions for spring as a whole.
Sea temperatures in the Tasman Sea are now slightly below average, although the oceans to the northeast of the North Island continue relatively warm for the time of year.