El Nino Watch
A combined ENSO index from NOAA PSL that blends 5 ocean and atmosphere variables over the tropical Pacific. Positive = El Nino-like.
Indices
MEI.v2 looks at the whole coupled system at once, not just ocean temperature. It combines 5 variables over the tropical Pacific (30° S-30° N, 100° E-70° W): sea-level pressure, sea surface temperature, east-west surface wind, north-south surface wind, and outgoing longwave radiation (a satellite measure of cloudiness).
It is computed for 12 overlapping 2-month "seasons" (DJ, JF, FM...) against a 1980-2018 reference period. The result is in standard deviations, like the NOAA SOI but with the opposite sign: positive = El Nino-like.
A high MEI together with a high ONI means ocean and atmosphere agree: the El Nino is well "coupled", which usually means stronger impacts.