Climate Summary for Autumn 2018
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New Zealand Climate Summary: Autumn 2018 Issued: 6 June 2018 A Warm Start to Autumn, Then Cooler and Unsettled at Times Temperature Nearly all of the North Island observed above average (0.51 to 1.20°C of average) temperatures during autumn, along with isolated pockets of near average (-0.50 to 0.50°C of average) and well above average (>1.20°C of average) temperatures. In the South Island, most locations recorded near average (-0.50 to 0.50°C of average) temperatures during autumn, with a handful of stations observing above average (0.51 to 1.20°C of average) temperatures. Rainfall Autumn rainfall in the North Island was generally near normal (80-119% of normal) or above normal (120-149% of normal), with a handful of locations also recording well above normal (>149% of normal) rainfall. In the South Island, above normal (120- 149% of normal) or well above normal (>149% of normal) rainfall was observed in most locations, with a few spots also recording near normal (80-119% of normal) rainfall. Soil moisture As of 1 June, soil moisture was near normal in most of the North Island, along with the western and southern South Island. However, soils were wetter or even much wetter than normal in small portions of the lower North Island and nearly all of the eastern South Island. Click on the link to jump to the information you require: Overview Temperature Rainfall Autumn climate in the six main centres Highlights and extreme events Overview Autumn 2018 began on a warm note, as March was characterised by significantly higher pressure than normal to the east of New Zealand. This pressure pattern, in concert with the decaying La Niña in the tropical Pacific, caused more northeasterly winds than usual over the country. Warm, humid air masses, combined with the remnants of the marine heatwave in the Tasman Sea, influenced higher than usual temperatures over New Zealand as well as some heavy rainfall events. However, the pressure pattern for April resulted in more southwesterly winds than normal for much of the country. Several low pressure systems and cold fronts passed over New Zealand, bringing adverse weather to many locations. Storms occurring on the 10th-11th and 28th-29th days of the month were particularly damaging with the former bringing destructive winds to Auckland, while the latter brought heavy rain to parts of the country, resulting in flooding and the declaration of a state of emergency in Rotorua. Refer to the highlights and extreme events section for further details. In May, mean sea level air pressures were much lower than normal over and to the south of New Zealand. The first half of the month was relatively warm and dry throughout the country. However, during the second half of May, a blocking anticyclone became established over the southeast of Australia, which delivered a prolonged period of disturbed westerly and southwesterly winds over the country. A ridge of high pressure covered the lower South Island during the final days of May, bringing heavy frosts and record cold temperatures to parts of Central Otago, Southland and the Mackenzie Basin. Further Highlights: • The highest temperature was 31.8°C, observed at Kawerau on 5 March. • The lowest temperature was -8.8°C, observed at Mt Cook Airport on 31 May. • The highest 1-day rainfall was 205 mm, recorded at Secretary Island on 19 March. • The highest wind gust was 187 km/hr, observed at Akitio on 21 May. • Of the six main centres in autumn 2018, Auckland was the warmest, Dunedin was the coolest and least sunny, Auckland and Wellington were the equal-wettest, Christchurch was the driest, and Tauranga was the sunniest. For further information, please contact: Mr Chris Brandolino Principal Scientist – Forecasting, NIWA National Climate Centre Tel. 09 375 6335, Mobile 027 866 0014 For climate data enquiries, please contact: Mr Seth Carrier Meteorologist/Forecaster, NIWA National Climate Centre Tel. 09 375 4508 Temperature: A Warm March, But Cooler April and May The nationwide average temperature in autumn 2018 was 13.8°C (0.6°C warmer than the 1981-2010 autumn average, using NIWA’s seven-station temperature series which begins in 1909). This makes the autumn of 2018 the 21st-warmest autumn on record. Mean temperatures for New Zealand were near average during April and May. However, the country observed its sixth-warmest March on record, with temperatures aided by a predominant northeasterly wind flow and well above average sea surface temperatures surrounding New Zealand. Nearly all of the North Island observed above average (0.51 to 1.20°C of average) temperatures during autumn, along with isolated pockets of near average (-0.50 to 0.50°C of average) and well above average (>1.20°C of average) temperatures. In the South Island, most locations recorded near average (-0.50 to 0.50°C of average) temperatures during autumn, with a handful of stations observing above average (0.51 to 1.20°C of average) temperatures. Despite the warm start to the season, notable cold snaps occurred during all three months, particularly in late-March, early-April, and finally in late-May. Below average temperatures were prevalent across much of the South Island in late-May, while the combination of low cloud and light winds allowed for several record cold maximum temperatures. Notably, on 31 May, Lauder only reached a maximum temperature of -2.6°C, which was a new May record with data going back to 1924. Tara Hills also set a new record on the same day, when the maximum temperature only reached -1.0°C. Records there date back to 1949. Record1 or near-record mean air temperatures for autumn were recorded at: Location Mean Departure Year Comments air from records o temp. normal ( C) began (oC) High records or near-records Akaroa 15.0 2.0 1978 2nd-highest Arapito 14.5 1.1 1978 2nd-highest Mokohinau 18.5 1.0 1994 2nd-highest Whitianga 16.8 1.5 1962 2nd-highest Hastings 15.5 1.2 1965 3rd-highest Motu 12.7 1.4 1990 3rd-highest Te Kuiti 15.3 1.2 1959 3rd-highest Wairoa 16.2 1.5 1964 3rd-highest Cheviot 12.7 0.9 1982 4th-highest Mahia 15.8 0.8 1990 4th-highest Motueka 14.0 1.2 1956 4th-highest Tauranga 16.9 1.2 1913 4th-highest Low records or near-records Kaikoura 12.2 -0.9 1963 4th-lowest Record or near-record mean maximum air temperatures for autumn were recorded at: Location Mean Departure Year Comments maximum from records o air temp. normal ( C) began (oC) High records or near-records Whitianga 22.0 1.8 1962 Highest Mokohinau 20.5 1.0 1994 2nd-highest Whangarei 21.8 1.1 1967 3rd-highest Hamilton (Ruakura) 21.6 1.8 1906 4th-highest Wairoa 21.5 1.7 1964 4th-highest Low records or near-records 1 The rankings (1st, 2nd, 3rd etc.) in all Tables in this summary are relative to climate data from a group of nearby stations, some of which may no longer be operating. The current climate value is compared against all values from any member of the group, without any regard for homogeneity between one station’s record, and another. This approach is used due to the practical limitations of performing homogeneity checks in real-time. Te Anau 13.6 -1.3 1963 2nd-lowest Manapouri (West Arm Jetty) 11.9 -1.2 1971 3rd-lowest Record or near-record mean minimum air temperatures for autumn were recorded at: Location Mean Departure Year Comments minimum from records o air temp. normal ( C) began (oC) High records or near-records Cheviot 6.9 1.3 1982 Highest Akaroa 10.8 2.7 1978 Highest Hastings 10.3 1.4 1965 2nd-highest Arapito 10.2 1.5 1978 2nd-highest Motueka 8.8 1.8 1956 2nd-highest Dargaville 13.8 1.4 1943 3rd-highest Port Taharoa 14.1 1.5 1973 3rd-highest Lower Retaruke 8.8 1.6 1966 3rd-highest Ngawi 13.0 0.9 1972 3rd-highest Paraparaumu 11.2 1.6 1953 3rd-highest Farewell Spit 12.6 1.7 1971 3rd-highest Culverden 7.1 1.8 1928 3rd-highest Cape Reinga 15.3 1.0 1951 4th-highest Whitianga 12.1 1.6 1962 4th-highest Tauranga 12.9 1.4 1913 4th-highest Taupo 9.1 2.0 1949 4th-highest Motu 7.9 1.4 1990 4th-highest Low records or near-records Kaikoura 6.9 -3.0 1963 2nd-lowest Rainfall: Variable Throughout the Season Autumn rainfall in the North Island was generally near normal (80-119% of normal) or above normal (120-149% of normal), with a handful of locations also recording well above normal (>149% of normal) rainfall. In the South Island, above normal (120-149% of normal) or well above normal (>149% of normal) rainfall was observed in most locations, with a few spots also recording near normal (80-119% of normal) rainfall. March rainfall was spatially patchy across New Zealand, with heavy rain leading to flooding in some areas, but stretches of dry weather for other locations. Notably, on 12 March, ex-Tropical Cyclone Hola affected the North Island. Heavy rain fell in eastern Northland, and around 100 mm of rain was recorded in parts of Coromandel and East Cape as the storm passed through. In April, much of the South Island received above normal or well above normal rainfall for the time of year, with the highest rainfall anomalies (departure from normal levels) occurring over eastern parts of Canterbury and Otago.