Island Climate Update 206 - November 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 October, sea surface temperatures (SSTs) in the central and eastern equatorial Pacific Ocean cooled substantially during the remainder of the month. This cooling was particularly significant in the far eastern Pacific, off the South American coast. The Southern Oscillation Index (SOI) has been positive since July 2017 and is currently at +0.9 (i.e. just below the La Niña threshold). In keeping with a positive SOI, trade winds along the equator are stronger than normal in the western half of the Pacific Ocean. Rainfall and convection anomalies in the tropical Pacific, which had been displaying a relatively strong La Niña-like pattern over the past few months, have however eased up.
In summary, the tropical Pacific Ocean has currently consistent La Niña-like signals in both the ocean and atmosphere. Some of these signals – notably SSTs in the eastern Pacific, and the SOI have intensified since early October 2017.
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.