This natural weather phenomenon, part of the El Niño-Southern Oscillation, or ENSO, occurs when warmer-than-average water extends throughout most of the equatorial Pacific Ocean just below the surface. That’s happening now. And powerful bursts of westerly wind have pushed immense amounts of warm water eastward, toward the Niño3.4 region where sea surface temperature, along with other atmospheric conditions, is used to assess the state of ENSO.