Mean sea level pressure was below normal over and to the southwest of New Zealand during August. This led to more westerly and northwesterly air flows than normal, which helped to keep air temperatures elevated during the month. This pressure setup influenced rainfall totals particularly in the South Island, where much of Canterbury and interior Otago experienced dry conditions for the time of year as these areas were sheltered from the prevailing wind flow by the Southern Alps.
Temperature
Mean temperatures were above average (+0.51°C to +1.20°C of the August average) for most of New Zealand, particularly the southern half of the North Island and the central and western South Island. Near average temperatures (-0.50°C to +0.50°C of the August average) were observed for most of the eastern South Island and northern and western North Island.
Rainfall
Rainfall was well below normal (<50% of the August normal) for most of Canterbury and interior Otago. Northland experienced below normal rainfall (50-79% of the August normal). Well above normal rainfall (>149% of the August normal) was observed in the Bay of Plenty and East Cape, as well as Nelson. Parts of Manawatu-Whanganui experienced above normal rainfall (120-149% of normal), and near normal rainfall was observed elsewhere (80-119% of normal).
Soil Moisture
As of 1 September 2018, soil moisture levels were above normal for the time of year in coastal Otago and Marlborough, as well as around coastal Gisborne. Slightly drier than usual soils were present in southern Hawke’s Bay, north Canterbury, and central Otago. Soil moisture levels were generally near normal for the time of year across the rest of the country.
