Rural Monthly Outlook:

Issued 1 August 2018

Get set for an unusually mild August

July 2018

Frequent and unsettled northwesterlies prevailed across the South Island during July, resulting in above average rainfall for western areas of the South Island,>but drier than usual conditions along the east coast. For the North Island,a mixture of prevailing westerlies and a ridge of high pressure produced well below normal rainfall for Gisborne, Hawkes Bay and the Wairarapa. In these regions, July rainfall totals ranked in the lowest handful (typically the 4th-6th driest July in the records). It was also relatively dry for Northland and the Bay of Plenty. Rainfall was close to normal elsewhere, with the exception of Kapiti, Horowhenua and Manawatu, where it was wetter than normal.

July temperatures were well above average across most of the South Island, as well as for the lower North Island. Elsewhere, monthly temperatures were closer to average.

The Ocean

Sea temperatures adjacent to the North Island coastline, and upper South Island coastline, continue below average for the time of year. However, waters around the lower half of the South Island and across most of the Tasman Sea remain warmer than usual.

During the last month, seas along the Pacific Ocean equator were observed to be slightly warmer than usual. Even so, the tropical climate system is currently still considered to be in a neutral state. However, the chance of El Nino has increased to around 65% during spring, and 70% in summer.

Over the last four months, the Southern Ocean has been switching regularly between positive mode (high pressures prevailing southeast of New Zealand,producing easterly winds) and negative mode (cooler southwesterlies or lows across the country). This switching is forecast to continue in August, with a full range of weather maps expected during the month. However, in addition,there is a strong signal for frequent Lows in the New Zealand region during August.

The August 2018 Outlook

The first half of August is forecast to run extremely mild, overall. The eastern South Island is expected to experience the largest deviations from what is normal at this time of year. The second half of the month is likely to run closer to average, nationally. Monthly temperatures should end up well above average for the east coast of the South Island, and above average elsewhere.

The weather recipe for August looks likely to be unsettled, and changeable.Normal-to-above-normal August rainfall totals are predicted for most regions of the country. The exceptions are Northland, Southland and Otago, with normal-to-below-normal monthly rainfall expected; and Canterbury (with closer to normal totals expected, but lower confidence in this prediction).

Bottom Line

Unusually mild in the first half of August, especially for the eastern South Island. A relatively unsettled month, with normal to above normal rainfall for most regions. The exceptions are Northland, Southland, and Otago (normal-to-below-normal monthly rainfall), and Canterbury (closer to normal monthly totals are forecast, with lower confidence).