NZ Climate Summary Feb 2018: Two ex-Tropical Cyclones
New Zealand Climate Summary: February 2018 Issued: 5 March 2018
Two ex-Tropical Cyclones Impact New Zealand
|Temperature||Mean temperatures were above average (0.51 to 1.20°C of average) or well above average (>1.20°C of average) across the North Island. Temperatures were more than 2°C above the February average for parts of Hawke’s Bay, Gisborne, and across lower Manawatu-Whanganui. In the South Island, temperatures were above average across the north and mostly near average (-0.50 to 0.50°C) across the central and south.|
|Rainfall||Rainfall was well above normal (>149% of normal) across much of the upper North Island, Wellington-Wairarapa, the upper South Island, Canterbury and Otago. Elsewhere, rainfall was above normal (120-149% of normal) or near normal (80-119% of normal).|
|Soil Moisture||As of 28 February, soils were wetter than normal for the time of year across the upper North Island and the central and upper South Island. Soil moisture was near normal elsewhere; although parts of Hawke’s Bay, Gisborne, and Southland had slightly below normal soil moisture.|
February 2018 was marked by two ex-Tropical Cyclones, Fehi and Gita, that impacted New Zealand on the 1st and 20th of the month, respectively. These two storms contributed to lower than normal sea level pressure that extended from the tropics to the north of New Zealand and southward across the country. The North Island had more northeast winds than normal, consistent with ongoing La Niña conditions, while the South Island observed only weak air flow anomalies. Sea surface temperatures (SSTs) in New Zealand coastal waters and across the Tasman Sea remained well above average during the month.
February was a contrasting month for temperatures, as the North Island experienced above (0.51 to 1.20°C of average) or well above average (>1.20°C of average) temperatures and the South Island had above average temperatures in the north and near (-0.50 to 0.50°C) or even slightly below average (-0.51 to -1.20°C of average) temperatures elsewhere. Many locations, particularly across the North Island, had near-record high mean monthly temperatures while just one South Island town (Clyde) observed near-record low mean monthly temperatures. The number of near-record high mean minimum temperatures outpaced near-record high mean maximums, and was a product of a very humid month marked by sub-tropical and tropical airflows, therein keeping overnight temperatures elevated.
The nationwide average temperature in February 2018 was 18.0°C (0.8°C above the 1981-2010 February average from NIWA’s seven station temperature series which begins in 1909).
The impact of ex-Tropical Cyclones Fehi and Gita led to above (120-149% of normal) or well above normal (>149% of normal) rainfall across parts of New Zealand during February. Rainfall totals in Tasman, Nelson, Marlborough, Canterbury, and Otago were 300 to 400% of the monthly normal in several locations. The lower North Island, including Wellington, experienced rainfall that was over 200% of the February normal as did northern Waikato, Auckland, and eastern Northland. In contrast, parts of Gisborne, Hawke’s Bay, Manawatu-Whanganui and Southland were somewhat sheltered from the moist northerly-quarter airflows and observed near normal (80-119% of normal) or even slightly below normal (50-79% of normal) rainfall.
By the end of February, soil moisture levels were much above normal for the time of year across the upper and central North Island as well as the upper and eastern South Island. In the Grey and Buller Districts as well as Otago, where medium-scale adverse drought events had previously been declared, soil moisture levels had recovered to near or above normal. Meanwhile, soil moisture levels in Southland, and the eastern North Island remained below normal for the time of year.
• The highest temperature was 34.9°C, observed at Christchurch (Riccarton) on 1 February.
• The lowest temperature was 0.9°C, observed at Mt Cook (Village) on 21 February.
• The highest 1-day rainfall was 267 mm, recorded at Milford Sound on 25 February.
• The highest wind gust was 161 km/h, observed at Cape Foulwind on 1 February.
• Of the six main centres in February 2018, Auckland and Tauranga were the warmest, Dunedin was the coldest and least sunny, Christchurch was the driest, Hamilton was the wettest, Wellington was the sunniest.
• Of the available automatic sunshine observation sites, the sunniest four locations in 2018 so far (1 January – 28 February) are Lake Tekapo (483 hours), Cromwell (481 hours), Paraparaumu (473 hours) and Richmond (471 hours).
2018 Climate Summary: Climate_Summary_February_2018_Final.pdf