Rural Monthly Outlook

A wet June, with volatile temperature swings

Issued 31 May 2019

May 2019 - An unusually dry month

Highs featured on the weather maps over New Zealand in May, keeping the rain makers away. It was an unusually dry May in the north and east of both Islands,even with the rain right at the end of the month. Many northern and eastern areas of the North Island recorded less than half of normal May rainfall.Abnormally low soil moisture continued across the North Island, especially north of Taupo. This reflects five months of higher than normal pressure over New Zealand, and five relatively dry months in a row.

Whangarei, Pukekohe, Hamilton, Taupo and Napier have all recorded less than 220mm of rain so far in 2019, based on data until the 30th. This is less than 40% of what is normal for Whangarei and about 50% of normal in the other areas.

May started out very cold across the North Island, but temperatures quickly rebounded to run extremely warm across the country for the remainder of the month.

The Ocean

Weak El Nino conditions remain in the tropical Pacific Ocean. No obvious impacts are expected here in the short term. The latest predictions continue this event into winter, but there remains uncertainty as to whether it will last into spring. The Southern Annular Mode (a measure of Southern Ocean storminess) remained strongly positive for much of May, encouraging high pressure in the New Zealand region. The last week of May saw a strong negative swing, eventually producing unsettled weather here. This unsettled phase is forecast to continue through the first half of June.

Sea surface temperature anomalies in the Tasman Sea and around New Zealand increased during May, under relatively light winds. Ocean temperatures are currently between 0.75C and 1.25C above normal around the country.

The June 2019 Outlook

June is traditionally an unsettled and wet time of year, with fronts and lows common across New Zealand. This forecast is referenced to that backdrop (climatology). In fact, the first two weeks of June 2019 are expected to run even more unsettled than normal. Frequent lows and rain bands are forecast to produce a relatively wet first half of June for all regions, before southerlies potentially show up in the third week of the month.

Volatile temperature swings are likely. This weekend runs extremely cold,before temperatures gradually shift back above average by mid-month. However, temperatures drop markedly again once the southerlies arrive. Overall, June temperatures are likely to run close to normal, if not a touch below normal - and this is in itself notable following abnormal warmth over the last 6 months.

Bottom Line

A wetter than usual June for all regions, with volatile temperature swings