Multiple indices are beginning to show a transition into El Nino signal territory, where the index in question shows that conditions similar to that of an El Nino are being seen. Above is the Global Atmospheric Angular Momentum, or GLAAM (also called AAM). If we look at past GLAAM values, we see that they have been staying in La Nina territory for a while now. However, I circled a new bounce in the GLAAM that has pushed the index into El Nino territory. Could this be a sign that the atmosphere is recognizing the El Nino? I wouldn't doubt it.
This second image is of the Global Wind Oscillation, or GWO. It is closely tied into the GLAAM, but pretty technical, so I'll just explain what it all means. Basically, the bottom half of the image (Phases 1-4) are defining a La Nina, and the top half of the image (Phases 5-8) are defining an El Nino. The middle circle, while colored, defines the GWO is too weak to affect the weather. Recently, the GWO has been staying in Phases 1-3, meaning weak La Nina conditions. However, if you follow the bright green line on the right half of the image, you will see the most recently observed conditions have been floating into Phase 4, going into an El Nino phase.
It appears that at least some of the atmosphere is starting to recognize the presence of an El Nino. While this is one of dozens of factors linked to seeing the El nino appear in the atmosphere, this is definitely a first step.