January 2018 was characterised by higher than normal sea level pressure to the east of New Zealand, and lower than normal sea level pressure to the west of the country. This pressure setup delivered more northerly-quarter winds than normal. Sea surface temperatures in New Zealand coastal waters and the Tasman Sea remained considerably higher than normal throughout the month.
January 2018 (New Zealand mean temperature 20.3°C; 3.1°C higher than the 1981-2010 January average) was New Zealand’s hottest month on record, which of course means it was additionally the country’s hottest January on record. Temperatures were well above average (>1.20°C of average) for the entire country, and locations in every region recorded either their record or near-record January temperature on record.
Rainfall was above normal (120-149% of normal) or well above normal (>149% of normal) throughout much of the top half of the South Island, as well as many areas of the North Island. Rainfall was below normal (50-79% of normal) or well below normal (<50% of normal) for much of Southland, Otago and Hawke’e Bay.
As of 31 January, soils were drier than normal for the time of year across large parts of Southland, Otago, the West Coast and Taranaki, as well as southern and eastern parts of the North Island. Soil moisture was above normal for eastern parts of Northland, Auckland, Bay of Plenty and Nelson.
Departure from average air temperature for January 2018.
End of month water balance in the pasture root zone for an average soil type where the available water capacity is taken to be 150 mm.