Current Climate - May 2014

May 2014 was characterised by lower pressures than normal to the south and west of New Zealand, with slightly higher than normal pressures to the north of the country.  

This pressure pattern resulted in an anomalous westerly flow over most of the country, bringing considerable rainfall to western and southern parts of the South Island, but relatively dry and sunny conditions for much of the North Island.

Rainfall

There was quite a contrast in rainfall observed across the country.  Many southern and western parts of the South Island received well above normal rainfall for the month (more than 150% of normal), whereas much of the North Island observed well below normal or below normal rainfall (less than 50% of normal and 50–79% of normal respectively).  It was especially wet about parts of Fiordland which received more than 200% of normal May rainfall.  Considerable spillover of rainfall from the Main Divide occurred in western Southland, the Southern Lakes and Central Otago where rainfall was also well above normal.  In contrast, Christchurch enjoyed a welcome respite from persistent heavy rainfall after an especially wet March and April, with the city observing below normal rainfall for May.  Rainfall was also below normal for many eastern, central and northern parts of the North Island.  It was an especially dry month about Kerikeri, Whangarei, Tauranga, Hicks Bay, Napier and Blenheim, with less than 30% of normal May rainfall recorded at these locations.

Temperature

Mean temperatures were above average (0.5 to 1.2°C) for the month of May across most of the South Island and parts of the southern and central North Island.  The exception was the Central Plateau, Nelson, coastal Westland near the glaciers and coastal Southland, where temperatures were near normal (within 0.5°C of May normal).  Well above average mean temperatures (more than 1.2°C above May average) were observed in limited inland parts of Westland, Canterbury and Otago, as well as some coastal locations in Canterbury. Air temperature anomalies over the North Island were generally more moderate than the South Island, with no locations observing well above average or well below average (more than 1.2°C below May average) temperatures.  Temperature anomalies observed over the North Island were generally higher in southern and central parts compared to remaining areas of the island, with temperatures above normal and near normal for those parts respectively.  The average or above average mean temperature observed throughout New Zealand in May occurred despite a cold snap that struck in the last week of the month, which brought snow to sea level over the southern South Island, and was followed by widespread frosts across New Zealand as an anticyclone became established over the country.  During this time, a number of North Island locations observed record or near-record low minimum temperatures for the month of May (see Highlights and extreme events - Temperatures section).  The nation-wide average temperature in May 2014 was 11.4°C (0.7C° above the 1971-2000 May average from NIWA’s seven station temperature series which begins in 1909).

Sunshine

May was a particularly sunny month for most of the North Island, with well above normal (more than 125% of May normal) or above normal (110-124% of May normal) recorded there.  Areas of coastal Manawatu-Whanganui and the Kapiti Coast were the exception, where sunshine was near normal (within 10% of May normal).  Sunshine was below normal in Fiordland (75-89% of May normal), well above normal in costal North Canterbury, and above normal in Canterbury north of Ashburton and South Otago.  Remaining parts of the South Island observed near normal sunshine.  Such sunshine anomalies are in keeping with the anomalous westerly flow occurring over most of the country in May: the effect of orography on this flow giving rise to increased cloud along western parts of the South Island and increased sunshine towards the east coast.

Soil Moisture

Despite a relatively dry month in Christchurch, soils there remained wetter than normal.  Soils were also wetter than normal throughout the eastern South Island, Central Otago and the Southern Lakes.  In the North Island, drier than normal soils persist for parts of Auckland and Northland, with considerable rainfalls required to bring soil moisture levels back to normal in those parts.  Soils about northern Gisborne, the Central Plateau and Hawke’s Bay are also drier than normal.  Soil moisture levels were near normal for most of the remaining areas of the New Zealand.