Frozen days punctuate unusually warm month
SEPTEMBER was warmer than usual for Otago and Southland, but the month did not come without a cold snap that broke several temperature records.
Niwa climate scientist Gregor Macara said temperatures were 0.51degC to 1.2degC above average in eastern parts of Otago during the month.
However, many areas observed record low September daily maximum temperatures on September 2830, when a bitterly cold southerly outbreak brought unseasonably cold temperatures to many parts of the South Island.
Dunedin Airport recorded a high of just 5.2degC on September 29 — the lowest high since records began in 1972.
Also recording the coldest September highs were Secretary Island (6degC), Puysegur Pt (6.2degC), Manapouri West Arm Jetty (1.9degC), and Alexandra (4.6degC).
Over the same period, Clyde recorded its equal lowest high with 5.7degC, and Oamaru, Balclutha and Nugget Pt recorded their secondlowest highs, Mr Macara said.
‘‘The prevalence of negative air temperatures at many low elevation coastal locations on September 29 indicates that the free air freezing level was situated at around sea level, which is particularly impressive given the time of year.’’
The cold air temperatures, combined with strong winds, resulted in severe wind chill factors, which created stress for livestock, and meant it felt much colder than the measured air temperature.
‘‘At Nugget Pt, between 9am and 10am, the lowest temperature was 1.1degC and the maximum wind gust was 137.1kmh, resulting in a temperature that felt as low as 13.5degC.’’
On any given day, the lowest daily temperatures usually occurred overnight, under clear skies and light winds, he said.
‘‘Remarkably, this wasn’t the case for several low elevation locations on September 29, where lowest daily temperatures were observed near the middle of the day.
‘‘Locations where this occurred included Dunedin (Musselburgh; 0.2degC between 10am and 11 am), Balclutha (0.7degC between 12pm and 1pm) and Tiwai Pt (1.5degC between 10am and 11am).
‘‘Perhaps most notably, Nugget Pt recorded its lowest ever September temperature of 1.4degC between 11am and midday.’’
The highest temperature of the month was 25.5degC, observed at Hanmer Forest on September 23, and the lowest was 7.5degC at Middlemarch on September 2.
Rainfall was above normal for western and central Otago and Southland, but well below normal for Dunedin, east and north Otago, and south Canterbury, Mr Macara said.
These areas were categorised as dry or very dry, according to Niwa’s New Zealand Drought Index.