Synopsis: La Niña is favoured to develop (~70% chance) during the Southern Hemisphere spring 2016 and slightly favoured to persist (~55% chance) during summer 2016-17.
ENSO-Neutral conditions were observed during September, with negative sea surface temperatures (SSTs) anomalies expanding across the eastern equatorial Pacific Ocean by early October. All of the Niño regions cooled considerably during late September and early October, with the latest weekly value of Niño-3.4 index at -0.9°C. Subsurface temperature anomalies also decreased toward the end of the month, reflecting the strengthening of below-average temperatures at depth in the east-central equatorial Pacific. Atmospheric anomalies across the equatorial Pacific edged toward La Niña during September, with a stronger tendency toward La Niña late in the month. The traditional Southern Oscillation index and the equatorial Southern Oscillation index were positive. The lower-level winds were near average across most of the basin during the month, but enhanced easterlies were becoming more persistent west of the International Date Line. Upper-level winds were anomalously westerly near and just east of the International Date Line. Convection was weakly suppressed over the central tropical Pacific and was more enhanced over Indonesia compared to last month. Overall, the combined ocean and atmosphere system reflects ENSO-Neutral during September, but are more clearly trending toward La Niña conditions.
The multi-model averages favour borderline Neutral-La Niña conditions (3-month average Niño-3.4 index less than or equal to -0.5°C) persisting during the Southern Hemisphere spring and continuing into the summer. Because of the recent cooling in the Niño-3.4 region and signs of renewed atmospheric coupling, the forecaster consensus now favours the formation of a weak La Niña in the near term, becoming less confident that La Niña will persist through the summer. In summary, La Niña is favoured to develop (~70% chance) during the Southern Hemisphere spring 2016 and slightly favoured to persist (~55%% chance) during summer 2016-17.
Almost all of the North Island should be slightly warmer than normal.
Near normal from Northland along the entire east coast of the North Island with near normal to slightly drier than normal conditions across from the far southern Waikato through to Wellington.
Almost all of the South Island should be moderately to considerably warmer than normal.
Near normal across the entire island but with slightly drier conditions in the west and moderately drier in the far southwest.