Summer 2019-20

Flooding in the south; drought in the north

Overview

Summer 2019-20 was characterised by lower than normal mean sea level pressure over the South Island and much lower than normal pressure to the south and east of New Zealand with higher than normal pressure to the northwest of the country. This pressure set up was associated with more westerly-quarter winds than normal and a persistently negative Southern Annular Mode during the first half of the season.

The persistent area of high pressure near the North Island was influenced by a strongly positive Indian Ocean Dipole pattern early in summer and by a warm pool of water in the tropical western Pacific Ocean later on. Climate change is expected to bring more frequent high pressure systems near and north of the North Island, similar to what occurred during summer 2019-20.

Nationwide temperatures during December and January were near average (-0.50°C to +0.50°C of the summer average) although some locations experienced above or well above normal temperatures during these months. February concluded summer on a warm note with a nationwide temperature that was above average (+0.51°C to +1.20°C of the summer average). For the summer season as a whole, temperatures were near average for much of the South Island with a large portion of Canterbury and parts of Otago and Tasman observing above average temperatures. Most of the North Island had above average temperatures although near average temperatures were experienced along much of the west coast and in parts of Gisborne and Waikato.

The nationwide average temperature for summer 2019-20 was near average at 17.1˚C (0.4°C warmer than the 1981-2010 summer average, using NIWA’s seven-station temperature series which begins in 1909).

December was very wet for many western and inland parts of the South Island, and this contributed to high lake levels and flooding events during the month. Conversely, January was very dry and most of the country received below normal (50-79% of the summer normal) or well below normal (<50% of the summer normal) rainfall with parts of upper North Island and upper and eastern South Island receiving less than 10% of their long-term rainfall normal during the month. By the end of January, meteorological drought was present in much of the upper North Island with severe meteorological drought in northern Auckland, Great Barrier Island, southern Northland, and the Aupouri Peninsula according to NIWA’s New Zealand Drought Index. Heavy rainfall in early February resulted in severe flooding across Fiordland, Otago, and Southland, particularly along the Mataura River, and several locations in the lower South Island observed record or near-record February rainfall amounts. Extremely dry conditions persisted in North Island and upper South Island throughout February, with rainfall totals that were below or well below normal. During this time, several locations experienced record or near-record long dry spells (see Highlights and extreme events for further details). By the end of February, drought conditions had spread across much of the North Island and severe meteorological drought was widespread across Northland, Auckland, and Great Barrier Island. Drought conditions were also present in several northern South Island locations, including parts of Tasman, northern Canterbury, and much of Marlborough.

For the season as a whole, the prolonged dry conditions in the North Island resulted in rainfall totals that were below normal, with well below normal rainfall observed in Auckland, Northland, parts of Waikato and the coast southeast of Napier. Small parts of Taranaki, Gisborne, and Greater Wellington received near normal rainfall totals (80-119% of the summer normal). In the South Island, above normal (120-149% of the summer normal) to well above normal (>149% of the summer normal) rainfall was observed in much of Southland, Otago and southern West Coast, owing to the periods of heavy rain occurring in December and February. The northern portion of the South Island mostly received near normal rainfall except coastal Canterbury between Christchurch and Kaikoura where rainfall was below normal.

Further highlights

• The highest temperature was 38.2˚C, observed at Gisborne on 31 January. This was New Zealand’s 5th-hottest January temperature on record.
• The lowest temperature of the month was -0.7˚C, observed at Hanmer Forest on 15, 16, and 17 January.
• The highest 1-day rainfall was 509 mm, recorded at Milford Sound on 3 February.
• The highest wind gust was 196 km/h, observed at Cape Turnagain on 5 January.
• Of the six main centres, Tauranga was the warmest, Dunedin was the coldest and wettest, Christchurch was the driest, Tauranga was the sunniest and Dunedin was the least sunny
• Of the available, regularly reporting sunshine observation sites, the sunniest four locations in 2020 so far are Bay of Plenty (618 hours), Taranaki (592 hours), Waikato (584 hours) and Auckland (564 hours).

Download

Climate Summary Summer 2019-2020 [PDF 540KB]