Rural Monthly Outlook:

Wild westerlies for August

Issued 2 August 2019

July 2019 - Unusually warm, with a sting in the tail

The first three weeks of July ran unusually warm, until an extreme cold outbreak at the end of the month produced several snowfalls and caused temperatures to plummet. Nevertheless, for many locations around the country, monthly temperatures will rank in the top 5 warmest Julys. The warmth was due to persistent northwesterlies, prior to the cold southerlies at the end of the month. Lower than normal pressures and unsettled weather affected the South Island during July, and not surprisingly, it was a wetter than normal month almost across the board there.

The exceptions were Southland and Clutha (drier than normal). Western regions of the North Island south of about Taumarunui also experienced above normal rainfall in July, as did Bay of Plenty and Taupo. In contrast, it was a relatively dry July for the east coast of the North Island, as well as for Northland. Auckland, Coromandel and Waikato saw closer to normal July totals.

The Ocean

The Southern Ocean has been driving the recent stormy weather patterns over New Zealand. The Southern Annular Mode (a measure of Southern Ocean storminess)showed intermittent unsettled (negative) spells during July and was extremely intense at the end of the month. Importantly, the Southern Ocean is forecast to continue strong negative (stormy) through the first half of August, and models show unsettled westerlies continuing for the second half of the month, too.

The southwesterly gales at the end of the month dramatically dropped the sea temperatures. At the end of July, sea temperatures anomalies around New Zealand were near 0C to 0.5C below normal.

The August 2019 Outlook

August is traditionally an unsettled and rather wet time of year, with frequent fronts passing over New Zealand. This forecast is referenced to that backdrop (climatology).

Well above normal August rainfall totals are expected along the West Coast South Island, with a wetter than usual August also expected for the western North Island, from Waikato down to Wellington. For Northland, Gisborne and Napier,things should run a touch drier than usual. In all other regions, near normal August rainfall totals are forecast.

Below average monthly temperatures are forecast for Otago and Southland,the Southern Lakes and Canterbury High Country. Near average August temperatures are predicted in all other regions.

Bottom Line

Wild westerlies for August. A wet August for the West Coast, as well as for Waikato to Wellington. A cold August for Otago, Southland,the Southern Lakes and Canterbury High Country; near average August temperatures elsewhere.