Global setting: October 2017

The tropical Pacific is still officially in a ENSO (El Niño Southern Oscillation) neutral state, but some indicators have leaned more towards La Niña conditions during the course of October 2017. After a brief period of warming early in the month, sea surface temperatures (SST) in the eastern equatorial Pacific Ocean have cooled significantly, especially off the South American coast. The NIWA Southern Oscillation Index has been positive since July 2017 and is currently at +0.9.

The international consensus is that the tropical Pacific Ocean will cool further over the next 3 months (November 2017 – January 2018), with La Niña conditions likely to be met over the same period (with 70% chance). However, the models indicate that if La Niña does develop, it is likely to remain in the weak category and be short-lived: a return to neutral conditions is most likely (58% chance) over the February-April 2018 period.

Sea Surface Temperatures

Coastal waters remain generally warmer than average around New Zealand, especially along the east coast of the South Island, where the anomaly for the month of October (estimated using data to the 28th October) exceeds +1oC. On the other hand, waters around the North Island have cooled compared to last month. The warmest ocean waters in the New Zealand region remain around and south of the Chatham Islands.

Differences from average global sea surface temperatures for 15 October - 11 November 2017. Map courtesy of NOAA Climate Diagnostics Centre https://www.esrl.noaa.gov/psd/map/images/sst/sst.anom.month.gif
Monthly values of the Southern Oscillation Index (SOI), a measure of changes in atmospheric pressures across the Pacific, and the 3-month mean (black line). SOI mean values: October SOI 0.9; August-October average 0.6.
Differences from average October surface temperatures in the seas around New Zealand