Here's another perspective based on a loop of the SST anomalies since late February, showing very nicely the development of the weak to moderate El Nino.
Concurrently, enhanced convection and cloud cover developed over most of the central and eastern tropical Pacific, especially just to the north of the equator along the Intertropical Convergence Zone (ITCZ). This is reflected in negative outgoing long-wave radiation (OLR) anomalies over the past month. More cloud cover (especially upper-level clouds) means less outgoing long wave radiation at the top of the atmosphere.
And, along with this convection, we've seen anomalous upper-level anticyclones to the north and south of the equator, the former associated with the active subtropical jet we've seen across the southwest the past couple of weeks.