Summer 2009-10

03 March 2010

Cold start, hot finish!

Rainfall: Very wet in Hawkes Bay, Wairarapa, Gisborne, Southland and the West Coast. Extremely dry in Northland, below normal rainfall in Auckland and east of the South Island.
Temperature: Cold start, hot finish – extreme temperatures along the way.
Soil moisture: Severe soil moisture deficits continued all summer in Northland, and developed by late summer in parts of Auckland, Marlborough, Canterbury and Otago.
Sunshine: Extremely sunny for the southern South Island and Northland. Very cloudy from Taranaki to Wellington.

It was a topsy-turvy summer. It started out extremely cold, with record cold temperatures in early December, but finished hot, with heat waves and above average temperatures in February. Overall, the New Zealand national average temperature for summer was near normal (16.6°C, 0.1°C below the long-term seasonal average). Summer temperatures were above average (between 0.5°C and 1.2°C above average) for Northland, Auckland, Coromandel, and the Bay of Plenty, as well as in inland and western areas of the South Island. Below average temperatures (between 1.2°C and 0.5°C below average) were observed about coastal Otago. Elsewhere, summer temperatures were close to normal.

Summer rainfalls were well above normal in Hawkes Bay, Wairarapa, Gisborne, and parts of Southland and the West Coast. In contrast, it continued extremely dry in Northland. Below normal rainfall also occurred in Auckland and the east of the South Island. Near normal summer rainfall was observed elsewhere. The most significant rainfall event of summer occurred on January 31st, affecting the eastern and central North Island, as well as Waikato and Coromandel. A moist, easterly air stream brought heavy rain and thunderstorms to these areas, causing flooding, slips, and road closures. Particularly hard hit were Gisborne and Hawkes Bay.

Summer sunshine totals were well above normal (more than 125 percent of normal) at either end of the country, with Kaitaia and Balclutha both experiencing their sunniest summer on record. In contrast, it was very cloudy (between 75 and 90 percent of normal sunshine hours) from Taranaki to Wellington.

Overall, it was an “El Niño” summer. Summer 2009/10 was characterised by more ‘highs’ in the Tasman Sea and over northern New Zealand, resulting in stronger than normal southwest winds over the country. This climate pattern resulted in well below average summer rainfall, and associated drought conditions, in Northland. Severe soil moisture deficits also developed by the end of summer in parts of Auckland, Marlborough, Canterbury and Otago, following a very dry February.

Major highlights

The highest summer temperature was 35.6°C recorded at Cheviot on February 22nd (2nd highest summer temperature at this site). The lowest summer temperature of -3.5°C was recorded at Lumsden on December 3rd (a new summer record at this site).
The highest 1-day summer rainfall was 203 mm recorded at Franz Josef on 6 January (not a record).
The peak wind gust was 182 km/hr recorded at Cape Turnagain on 12 December (not a record).
Of the six main centres this summer, Tauranga was the warmest and sunniest, Dunedin the coolest, Hamilton the wettest, and Christchurch the driest.