Although this is not a notification or RSS feed, it might still help you. The following two web sites give El Nino information, updated once or twice a month:

http://www.cpc.ncep.noaa.gov/products/analysis_monitoring/enso_advisory…  is updated the morning of the 2nd Thursday of each month.

http://iri.columbia.edu/our-expertise/climate/forecasts/enso/current/?e…  is updated at same time as the above site, and also on the 3rd Thursday of the month (most often in the afternoon).

The second site above has branches into various other aspects of El Nino and La Nina, some giving meaty technical information, which I don't know would please you or turn you off.