Island Climate Update 217 - October 2018
For the sixth consecutive month, ENSO-neutral conditions persisted across the tropical Pacific. Sea surface temperatures (SSTs)in the central and eastern equatorial Pacific remained in the neutral range. Anomalies for the conventional NINO3.4 index remain just under the +0.3°C mark.
In the subsurface ocean, positive temperature anomalies (centred around 150m depth) expanded towards the eastern Pacific and strengthened during September 2018. These anomalies at depth are associated with large heat content anomalies (> +2°C) being centred just west and over the International Dateline, again a signal consistent with the potential for a Modoki (i.e. central Pacific) rather than a canonical, eastern Pacific El Niño event.
The Southern Oscillation Index (SOI) was negative with a value of –1 for September 2018. Trade winds during September 2018 were slightly weaker than normal over much of the tropical Pacific. The last week of September saw the emergence of a westerly wind burst (WWB), associated with a reversal of the climatological easterly trade winds west of 160oE. This WWB, along with the sizeable heat content anomalies in the central Pacific is expected to eventually tip the ocean –atmosphere system towards what is shaping to be a late-onset El Niño event.
The consensus from international models is for the tropical Pacific to transition towards El Niño over the next three-month period (68% chance over October –December 2018). The probability for El Niño conditions being established remains high into the autumn of 2019, with a 71% chance for El Niño conditions over the April –June 2019 period. Almost all models are consistent in pointing towards a weak El Niño.