Niwa: Regional predictions for the next three month
Regional predictions for the next three months:
NIWA Outlook: August-October 2015
Overview
El Niño conditions continued to strengthen during July 2015. Sea surface temperature anomalies in the eastern and central Equatorial Pacific have been exceeding +1oC for the past two months. The Southern Oscillation Index (SOI) was strongly negative (-1.3 for July 2015, value estimated on the 30th of July) and westerly wind anomalies (weaker trade-winds) dominated the central and western equatorial Pacific.
International guidance indicates that El Niño is virtually certain (97% chance) to continue over the next three months period (August – October 2015) and extremely likely (above 90% chance) to persist into the summer 2015 / 2016.
During August – October 2015, above normal pressure is forecast over and to the south of Australia, while below normal pressure is expected well to the northeast of New Zealand. This circulation pattern is likely to be accompanied with anomalous south-westerly winds, which is typical of an El Niño influence during winter-spring.
Sea surface temperatures for the coming three months are expected to be near average around the coasts of New Zealand.
Outlook Summary
August – October 2015 temperatures are about equally likely (35-40% chance) to be average or below average in all regions of New Zealand. Note that cold snaps and frosts are to be expected in some parts of the country from time to time.
August – October 2015 rainfall totals are about equally likely (40 to 45% chance) to be in the near normal or below normal range for all regions of New Zealand except for the west of the South Island, where near normal or above normal rainfall is about equally likely (35-40% chance).
Soil moisture and river flow are most likely (45 to 65% chance) to be in the below normal range for the north of the North Island and the east of the South Island. In the west of the South Island, soil moisture levels and river flows for the August – October 2015 season as a whole are most likely (45 – 50% chance) to be in the above normal range. Soil moisture and river flows are equally likely (40% chance) to be near normal or below normal in the east of the North Island and the north of the South Island. In the west of the North Island, soil moisture levels are most likely (45% chance) to be in the near normal range, while river flows are equally likely (40% chance) to be in the near normal or below normal range.
Regional predictions for the August to October season
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 equally likely (40% chance) to be near average or below average.
• Rainfall totals are about equally likely (40-45% chance) to be in the normal or below normal range.
• Soil moisture levels and river flows are most likely (45-50% chance) to be in the below normal range.
Other outcomes cannot be excluded. The full probability breakdown is:
Temperature | Rainfall | Soil moisture | River flows | |
Above average | 20 | 15 | 20 | 20 |
Near average | 40 | 40 | 35 | 30 |
Below average | 40 | 45 | 45 | 50 |
Central North Island, Taranaki, Wanganui, Manawatu, Wellington
Probabilities are assigned in three categories: above average, near average, and below average.
• Temperatures are equally likely (40% chance) to be near or below average.
• Rainfall totals and river flows are equally likely (40% chance) to be in the below normal or near normal range.
• Soil moisture levels are most likely (45% chance) to be in the near normal range.
The full probability breakdown is:
Temperature | Rainfall | Soil moisture | River flows | |
Above average | 20 | 20 | 20 | 20 |
Near average | 40 | 40 | 45 | 40 |
Below average | 40 | 40 | 35 | 40 |
Gisborne, Hawke’s Bay, Wairarapa
Probabilities are assigned in three categories: above average, near average, and below average.
• Temperatures are about equally likely (35-40% chance) to be average or below average.
• Rainfall totals are about equally likely (40-45% chance) to be in the below normal or near normal range.
• Soil moisture levels and river flows are equally likely (40% chance) to be in the near normal or below normal range.
The full probability breakdown is:
Temperature | Rainfall | Soil moisture | River flows | |
Above average | 25 | 15 | 20 | 20 |
Near average | 35 | 40 | 40 | 40 |
Below average | 40 | 45 | 40 | 40 |
Nelson, Marlborough, Buller
Probabilities are assigned in three categories: above average, near average, and below average.
• Temperatures are about equally likely (35-40% chance) to be near average or below average.
• Rainfall totals are about equally likely (40-45% chance) to be in the below normal or near normal range.
• Soil moisture levels and river flows are equally likely (40% chance) to be in the near normal or below normal range.
The full probability breakdown is:
Temperature | Rainfall | Soil moisture | River flows | |
Above average | 25 | 15 | 20 | 20 |
Near average | 40 | 40 | 40 | 40 |
Below average | 35 | 45 | 40 | 40 |
West Coast, Alps and foothills, inland Otago, Southland
Probabilities are assigned in three categories: above average, near average, and below average.
• Temperatures are about equally likely (35-40% chance) to be in the near average or below average range.
• Rainfall totals are about equally likely (35-40% chance) to be in the near normal or above normal range.
• Soil moisture levels and river flows are most likely (45-50% chance) to be in the above normal range.
The full probability breakdown is:
Temperature | Rainfall | Soil moisture | River flows | |
Above average | 25 | 40 | 45 | 50 |
Near average | 35 | 35 | 35 | 30 |
Below average | 40 | 25 | 20 | 20 |
Coastal Canterbury, east Otago
Probabilities are assigned in three categories: above average, near average, and below average.
• Temperatures are equally likely (40% chance) to be in the near average or below average range.
• Rainfall totals are about equally likely (40-45% chance) to be in the near normal or below normal range.
• Soil moisture levels and river flows are most likely (55-65% chance) to be in the below normal range.
The full probability breakdown is:
Temperature | Rainfall | Soil moisture | River flows | |
Above average | 20 | 15 | 15 | 10 |
Near average | 40 | 45 | 30 | 25 |
Below average | 40 | 40 | 55 | 65 |
ENDS