El Nino Watch
An average over a window that slides forward in time. It removes short-lived ups and downs so the trend is easier to see.
Indices
A 3-month running mean averages months 1-2-3, then 2-3-4, then 3-4-5, and so on. It smooths out week-to-week noise (a passing storm can cool the ocean for a few days).
The price: it lags. A 3-month mean centred on July is only complete at the end of August and is published in early September. That is why the app also shows weekly and daily Nino 3.4 values, which are faster but noisier.