CPC adopts Relative Oceanic Niño Index (RONI)
for reliable, responsive monitoring and tracking of ENSO

February 2026

The Climate Prediction Center is making the shift to use the Relative Oceanic Niño Index (RONI) to better designate past events and predict future ENSO. The traditional Oceanic Niño Index (ONI) relies on a departure from 30-year average that struggles to keep pace with anomalous changes in tropical sea surface temperature (SST), which is particularly problematic in real-time when using a time lagged climatology. RONI solves this problem by comparing the ENSO region to the global tropics, thereby reducing the dependency on the climate base period. Read more on the information circular below.