Regional climates around the world display cycles corresponding to the 18.61‐year maximum lunar declination (MLD) periodicity. We suggest that these cycles are created by a relationship between MLD and El Niño / Southern Oscillation (ENSO). Both equatorial Pacific sea‐surface temperature and South Pacific atmospheric pressure significantly correlate with maximum lunar declination. Low MLDs are associated with warmer equatorial Pacific sea‐surface temperatures and negative values of the Southern Oscillation Index. A lunar‐influenced change in the Pacific gyre circulation presents a viable physical mechanism for explaining these relationships. We suggest that the gyre is enhanced by tidal forces under high MLDs, inducing cold‐water advection into the equatorial region but is restricted by the weak tidal forcing of low MLDs thereby favoring El Niño episodes. An astronomical model utilizing this relationship produces a forecast of increased non‐El Niño (either La Niña or neutral) activity for the early part of this decade.