Rural Monthly Outlook:

A drier than normal April forecast for the South Island


3 April 2019

March 2019 - An extreme month

After a cold start to the month, March temperatures quickly rebounded to well above average levels, and stayed that way across the month. Many South Island locations recorded monthly temperatures more than 2 degrees above the norm,which equates to record, or near-record, March warmth. Across the North Island,monthly temperatures were around 1.5 degrees above the March average,which is still significant.

Rainfall wise, March ran relatively dry for the first three weeks of the month, even with the odd rain band making inroads into the prevailing high pressure over the country. However a major northwesterly front on the 25th and 26th produced extreme rainfall on the West Coast South Island, as well as lesser amounts for Nelson and Taranaki. Rainfall of 500 to 700 mm was widely experienced along the Southern Alps, with some alpine areas recording 700 to 1100 mm of rain. A State of Emergency was declared for Westland on 26 March,after roads and bridges were washed away, and major flooding occurred.

Overall, the monthly rainfall totals were below half of March normal across northern and eastern parts of the North Island, and also along the eastern and southern coastlines of the South Island. Soils remain unusually dry in these areas. Taranaki to Tongariro saw closer to normal monthly rainfall tallies,while it was extremely wet for the west and north of the South Island.

The Ocean

El Nino conditions remain marginal in the tropical Pacific Ocean. While no obvious impacts are expected here in New Zealand in the short term, it may be that this El Nino becomes important (has some teeth) if it hangs around until spring. Sea surface temperatures in the Tasman Sea and around New Zealand continue to be well above average (around 1.5 degrees above normal).

The April 2019 Outlook

This week, high pressure will favour the South Island, with prevailing southeasterlies over the North Island. The Tasman Sea is subsequently going to become the primary weather driver next week (week two) and into week three.Lows forming over the Tasman Sea and extending onto the North Island are forecast to be the main players around the middle of April. This is expected to result in prevailing easterlies across the North Island for weeks two and three of the month, while high pressure favours the south of the country.

This week, air temperatures run below average for the time of year. However, temperatures are forecast to rebound back to above average over the South Island from next week, and across northern and western regions of the North Island from about the middle of the month. Rainfall wise, the month has started with a decent burst of rain for western and northern parts of the North Island.

Looking ahead,there is a somewhat drier than usual signal for all regions of the country, except for the east coast North Island. This should result in a drier than usual April for the South Island, with near normal totals across the North Island.

Bottom Line

April starts cooler, but ends warmer than usual. A drier April for the South Island; near normal April totals for the North Island.