NOAA Climate Prediction Center: "ENSO Alert System Status: La Niña Watch "

We usually just post the plume of the model runs, which currently are pointing to neutral conditions:

but the fact the diagnostic discussion is making a point of the watch means we're going to pay attention to possible development.

From the CPC:

14 September 2017

ENSO Alert System Status: La Niña Watch

Synopsis:  There is an increasing chance (~55-60%) of La Niña during the Northern Hemisphere fall and winter 2017-18. Over the last month, equatorial sea surface temperatures (SSTs) were near-to-below average across the central and eastern Pacific Ocean [Fig. 1]. ENSO-neutral conditions were apparent in the weekly fluctuation of Niño-3.4 SST index values between -0.1°C and -0.6°C [Fig. 2]. While temperature anomalies were variable at the surface, they became increasingly negative in the sub-surface ocean [Fig. 3], due to the shoaling of the thermocline across the east-central and eastern Pacific [Fig. 4]. Though remaining mostly north of the equator, convection was suppressed over the western and central Pacific Ocean and slightly enhanced near Indonesia [Fig. 5]. The low-level trade winds were stronger than average over a small region of the far western tropical Pacific Ocean, and upper-level winds were anomalously easterly over a small area of the east-central Pacific. Overall, the ocean and atmosphere system remains consistent with ENSO-neutral.  A majority of the models in the IRI/CPC suite of Niño-3.4 predictions favor ENSO-neutral through the Northern Hemisphere 2017-18 winter [Fig. 6]. However, the most recent predictions from the NCEP Climate Forecast System (CFSv2) and the North American Multi-Model Ensemble (NMME) indicate the formation of La Niña as soon as the Northern Hemisphere fall 2017 [Fig. 7]. Forecasters favor these predictions in part because of the recent cooling of surface and sub-surface temperature anomalies, and also because of the higher degree of forecast skill at this time of year. In summary, there is an increasing chance (~55-60%) of La Niña during the Northern Hemisphere fall and winter 2017-18 (click CPC/IRI consensus forecast for the chance of each outcome for each 3-month period).... MORE