Rural Monthly Outlook:

Issued 4 April 2018

A changeable month ahead

March 2018

High pressures prevailed to the east of New Zealand during March, with ridging extending over the lower South Island. Frequent northeasterly winds occurred during the month. Air temperatures were above average, overall, particularly for western and southern regions of the South Island. It was the warmest March on record for Westport and Invercargill, in records that began in 1937 and 1948,respectively. It was also unusually mild elsewhere along the West Coast, with Milford Sound and Hokitika both experiencing their third-equal warmest March on record. Nelson observed its fourth warmest March, in 75 years of records.

Rainfall totals were above normal across most of the North Island, although there were pockets with drier conditions (60-80 percent of March normal) across South Auckland and the Waikato, and for inland and eastern parts of the Bay of Plenty. It was a wetter than normal March for Nelson and Fiordland, but a drier than usual month for much of Southland. Elsewhere in the South Island, rainfall was highly variable from location to location.

The Ocean

Sea temperatures over the Tasman Sea and around the New Zealand coastline continued to ease during March. Sea temperatures were between 1 and 1.5 degrees above average around the north and west of the North Island, and were about 2 degrees above average around most of the South Island shoreline. Sea temperatures around Cook Strait, including off Marlborough and the Wairarapa coastline, have cooled considerably, and are now running average to cooler.

Neutral climate conditions are currently observed in the tropical Pacific Ocean ( with neither La Nina nor El Nino in play at this time). More importantly, the Southern Annular Mode (SAM) recently flipped into its negative mode, producing stronger westerlies across the South Island. The SAM is expected to stay negative for the first half of April, continuing the theme of active weather systems.

The April 2018 Outlook

At the start of the month, westerlies prevail across the South Island, with a ridge of high pressure keeping things rather dry over the North Island. However,as we move into next week, a couple of active fronts affect the country. Expect an unsettled period for both Islands, with respect to both precipitation and temperature swings. A very cold southerly outbreak is indicated early next week,with potential for heavy snowfall, meaning that keeping up with the forecasts will be essential. Just after mid-month, we may see a brief quiet spell over New Zealand - but it isn't likely to last long. Active weather looks likely to return three quarters the way through the month. Overall, above normal April rainfall is forecast for the West Coast of the South Island and Southland.Normal to above normal rainfall is signalled from Taranaki down to Wellington,too. The northern half of the North Island should stay on the drier side of the ledger - but still expect a couple of decent fronts next week. April rainfall totals are forecast to be near normal in all other regions, although the month itself signals as very changeable.

Bottom Line

A changeable April. Temperatures bounce strongly during the month, ending up closer to average, overall, than seen at any point in the last six months. A very wet month for the West Coast South Island and Southland, also normal to above normal totals for Taranaki down to Wellington. Slightly drier than usual for Taupo northwards. Elsewhere, near normal April rainfall.