July 2013 was characterised by much higher pressures than normal over and to the north, east, and west of New Zealand. Persistent lower pressures than normal were present well to the south of the country. This pressure pattern caused largely settled conditions over New Zealand for July, resulting in high mean temperatures for the time of year in much of the South Island and parts of the North Island, and dry conditions in the northern half of the North Island and eastern South Island.
New Zealand Climate Update 170 – August 2013
What happened in July, how our climate outlook for the previous three months turned out, global and local sea temperatures, and our outlook for August to October.
The equatorial Pacific Ocean as a whole remains in a neutral state (neither El Niño nor La Niña) despite the persistence of colder than normal Sea Surface Temperatures (SSTs) in the eastern equatorial Pacific. International guidance indicates that ENSO-neutral is the most likely outcome for the next three months (August–October). For the New Zealand region, higher pressures than normal are forecast south of the country, while lower pressures than normal are expected to the north over Australia and the Coral Sea. This circulation pattern is expected to produce a weaker than normal westerly flow over the country.
Rainfall for the August–October period as a whole is forecast to be normal or above normal in the east and north of the North Island as well as the west of the South island, while normal or below normal rainfall is likely for the west of the North Island and the north of the South Island. Normal rainfall is expected for the east of the South Island.
For May-July 2013 higher pressures than normal were forecast south of the country extending towards the east of the Chatham Islands. Lower pressures than normal were expected to the north of New Zealand. This circulation pattern was expected to produce weaker than normal westerly flows. Actual pressures for this 3-month period were weak across the New Zealand region, with strongly negative mean sea level anomalies to the south and more positive anomalies to west and east of the country. This mixed pattern resulted in weak south-west flows across southern areas and weak easterly flows across northern areas of New Zealand.