Pictured: The Nino SSTA regions across the central and eastern equatorial Pacific Ocean indicate marginal El Nino (left). In the equatorial subsurface of the Pacific Ocean a large area of warmth is in the West Pacific to just east of the Dateline while weak cool anomalies are in the East Pacific.
As late spring in the northern hemisphere arrives ENSO phase remains neutral. The Nino SSTA regions are right on the defining boundary of El Nino (+0.5C SSTA in the Nino34 region) since mid-April but at least 3 months of this observation is required before El Nino onset can generate. The subsurface equatorial East Pacific is near to cooler than normal indicating lack of fuel to generate and maintain El Nino. The subsurface equatorial West Pacific to the Dateline is quite warm as a Kelvin Wave appears to be generating. An eastward shift of this subsurface warmth near the Dateline would cause El Nino risk to increase. To push the subsurface warmth eastward into the East Pacific would require trade winds to shut down. These conditions can be initiated by a transient Madden Julian oscillation. The MJO has been active in 2017 so far therefore monitoring of a potential El Nino the second half of 2017 remains possible but as of now there are no signs of a change in neutral ENSO.
