Climate

A warm and dry month for much of New Zealand.

During October, the NINO3.4 Index anomaly (central Pacific) was 0.86˚C. The NINO 1+2 Index (eastern Pacific) was 0.56 C. Upper oceanic heat content continued to decrease in the east central part of the Pacific basin. Heat content continued to be higher than normal in the western Pacific. Overall, the pattern is consistent with La Niña conditions.

November 2020 – January 2021 air pressure is forecast to be higher than normal over and to the southeast and lower than normal to the northwest of New Zealand. This is expected to be associated with northeasterly air flow anomalies, a signature of La Niña.

The NIWA and MetService assessment of named tropical cyclone (TC) activity indicates 8 to 10 named TCs could occur in the Southwest Pacific basin between November 2020 and April 2021. This seasonal outlook is for normal to below normal activity in terms of overall named cyclone systems in the region.

During September, the NINO3.4 Index anomaly (central Pacific) was 0.71˚C. The NINO 1+2 Index (eastern Pacific) was 0.76 C. Upper oceanic heat content remained lower than normal with continued decreases observed in the east central part of the Pacific basin since August. Heat content continued to be higher than normal in the western Pacific. Overall, the pattern is consistent with La Niña conditions.

Dry for northern North Island, wet for much of South Island.

Air pressure is forecast to be higher than normal to the southeast and lower than normal to the north of New Zealand. This is expected to be associated with developing La Niña-like northeasterly air flow anomalies, although a westerly flow anomaly, which may be strong at times, is favoured to continue for much of October.