The El Niño/ Southern Oscillation and Oceanic Niño Index

ENSO stands for El Niño/ Southern Oscillation. The ENSO cycle refers to the coherent and sometimes very strong year-to-year variations in sea- surface temperatures, convective rainfall, surface air pressure, and atmospheric circulation that occur across the equatorial Pacific Ocean. El Niño and La Niña represent opposite extremes in the ENSO cycle.
El Niño refers to the above-average sea-surface temperatures that periodically develop across the east-central equatorial Pacific. It represents the warm phase of the ENSO cycle, and is sometimes referred to as a Pacific warm episode.
During an El Niño or La Niña, the changes in Pacific Ocean temperatures affect the patterns of tropical rainfall from Indonesia to the west coast of South America, a distance covering approximately one-half way around the world. These changes in tropical rainfall affect weather patterns throughout the world including the United States. The Oceanic Niño Index (ONI) is based on SST departures from average in the Niño 3.4 region, and is a principal measure for monitoring, assessing, and predicting ENSO. All information and data is from the NOAA Climate Prediction Center.

The Oceanic Niño Index (ONI)

Year/Month JAN FEB MAR APR MAY JUN JUL AUG SEP OCT NOV DEC
2018 -0.90 - - - - - - - - - - -
2017 -0.33 0.02 0.12 0.30 0.45 0.41 0.28 -0.21 -0.51 -0.60 -1.01 -1.04
2016 2.66 2.34 1.70 0.99 0.39 0.05 -0.44 -0.63 -0.65 -0.78 -0.80 -0.55
2015 0.61 0.52 0.56 0.79 1.01 1.25 1.49 1.88 2.12 2.32 2.67 2.60
2014 -0.39 -0.51 -0.19 0.18 0.41 0.31 -0.03 -0.08 0.21 0.40 0.71 0.66
2013 -0.43 -0.41 -0.16 -0.15 -0.31 -0.35 -0.36 -0.44 -0.26 -0.24 -0.19 -0.22
2012 -0.77 -0.57 -0.52 -0.40 -0.23 0.10 0.28 0.41 0.30 0.22 0.11 -0.30
2011 -1.44 -1.00 -0.83 -0.67 -0.43 -0.30 -0.39 -0.70 -0.88 -1.09 -1.23 -1.11
2010 1.61 1.35 0.98 0.48 -0.13 -0.61 -1.04 -1.44 -1.67 -1.73 -1.69 -1.65
2009 -0.79 -0.69 -0.61 -0.26 0.15 0.39 0.52 0.51 0.60 0.85 1.40 1.68
2008 -1.58 -1.56 -1.12 -0.90 -0.75 -0.61 -0.27 -0.18 -0.33 -0.39 -0.50 -0.91
2007 0.80 0.23 -0.09 -0.22 -0.38 -0.28 -0.55 -0.77 -1.19 -1.43 -1.58 -1.63
2006 -0.81 -0.57 -0.62 -0.22 0.00 0.08 0.04 0.25 0.52 0.66 0.95 1.09
2005 0.76 0.46 0.53 0.35 0.39 0.12 -0.19 -0.10 -0.11 -0.10 -0.64 -0.97
2004 0.38 0.34 0.21 0.16 0.14 0.20 0.51 0.70 0.72 0.68 0.61 0.69
2003 0.70 0.74 0.45 -0.05 -0.52 -0.21 0.24 0.20 0.19 0.38 0.29 0.38
2002 -0.05 0.06 0.09 0.12 0.40 0.79 0.77 0.81 1.01 1.20 1.41 1.31
2001 -0.63 -0.53 -0.39 -0.39 -0.24 -0.11 -0.01 -0.10 -0.28 -0.18 -0.41 -0.46
2000 -1.77 -1.53 -0.93 -0.75 -0.74 -0.64 -0.55 -0.47 -0.52 -0.65 -0.71 -0.88
1999 -1.69 -1.31 -0.90 -1.00 -1.02 -1.05 -1.05 -1.19 -1.09 -1.19 -1.50 -1.70
1998 2.37 2.03 1.38 0.90 0.70 -0.24 -0.86 -1.25 -1.26 -1.41 -1.38 -1.64
1997 -0.54 -0.36 -0.20 0.27 0.76 1.22 1.67 1.91 2.12 2.40 2.48 2.32
1996 -0.86 -0.85 -0.56 -0.36 -0.26 -0.30 -0.32 -0.20 -0.45 -0.40 -0.34 -0.61
1995 0.98 0.71 0.48 0.41 0.02 -0.01 -0.11 -0.61 -0.90 -0.92 -1.10 -1.00
1994 0.06 0.03 0.11 0.38 0.43 0.44 0.35 0.54 0.41 0.71 1.11 1.19
1993 0.10 0.38 0.40 0.71 0.91 0.48 0.33 0.15 0.29 0.02 0.01 0.10
1992 1.78 1.74 1.38 1.32 1.16 0.70 0.33 0.07 -0.13 -0.34 -0.28 -0.21
1991 0.45 0.29 0.05 0.32 0.40 0.65 0.86 0.69 0.36 0.82 1.19 1.62
1990 0.11 0.31 0.20 0.33 0.34 0.21 0.37 0.42 0.35 0.40 0.31 0.48
1989 -1.87 -1.37 -1.05 -0.82 -0.61 -0.29 -0.30 -0.33 -0.18 -0.22 -0.25 -0.01
1988 0.99 0.37 0.25 -0.19 -1.00 -1.44 -1.45 -0.99 -0.87 -1.71 -1.85 -1.83
1987 1.22 1.23 1.13 0.82 0.88 1.21 1.57 1.76 1.77 1.42 1.27 1.07
1986 -0.56 -0.60 -0.26 -0.08 -0.27 -0.01 0.17 0.51 0.65 0.98 1.20 1.24
1985 -1.17 -0.71 -0.67 -0.93 -0.75 -0.65 -0.47 -0.35 -0.55 -0.30 -0.20 -0.32
1984 -0.69 -0.18 -0.39 -0.44 -0.46 -0.63 -0.24 -0.04 -0.19 -0.49 -1.00 -1.25
1983 2.32 1.94 1.49 1.19 1.18 0.82 0.17 -0.04 -0.36 -0.96 -1.10 -0.94
1982 0.11 -0.15 0.25 0.45 0.72 0.80 0.64 0.93 1.64 2.16 2.09 2.28
1981 -0.38 -0.62 -0.51 -0.29 -0.30 -0.19 -0.37 -0.32 -0.04 -0.11 -0.23 -0.11
1980 0.70 0.39 0.28 0.34 0.51 0.59 0.28 -0.11 -0.07 -0.02 0.14 0.22
1979 0.03 -0.04 0.23 0.42 0.19 0.08 -0.13 0.16 0.48 0.35 0.53 0.69
1978 0.78 0.42 0.06 -0.30 -0.31 -0.33 -0.22 -0.53 -0.50 -0.23 -0.14 0.11
1977 0.93 0.55 0.44 0.03 0.22 0.39 0.42 0.25 0.60 0.86 0.72 0.86
1976 -1.84 -1.09 -0.58 -0.53 -0.31 -0.00 0.17 0.38 0.50 0.98 0.95 0.66
1975 -0.32 -0.53 -0.86 -0.58 -0.76 -1.15 -1.04 -1.20 -1.37 -1.54 -1.38 -1.73
1974 -1.95 -1.50 -1.21 -0.97 -0.91 -0.85 -0.55 -0.21 -0.35 -0.66 -0.82 -0.78
1973 1.92 1.34 0.49 -0.19 -0.59 -0.83 -1.18 -1.31 -1.36 -1.69 -2.09 -2.06
1972 -0.78 -0.30 0.03 0.45 0.75 0.80 1.20 1.40 1.52 1.83 2.17 2.28
1971 -1.60 -1.42 -1.13 -0.80 -0.61 -0.78 -0.82 -0.79 -0.71 -0.96 -0.88 -1.03
1970 0.48 0.41 0.13 0.34 0.10 -0.31 -0.70 -0.87 -0.70 -0.73 -0.78 -1.06
1969 1.14 1.31 0.81 0.73 0.76 0.35 0.18 0.56 0.81 1.01 0.76 0.66
1968 -0.66 -0.86 -0.68 -0.30 -0.34 0.52 0.66 0.54 0.38 0.42 0.85 0.94
1967 -0.48 -0.44 -0.51 -0.66 -0.18 0.12 0.06 -0.03 -0.49 -0.36 -0.28 -0.38
1966 1.31 1.00 1.19 0.76 0.02 0.29 0.42 0.02 -0.07 -0.11 -0.12 -0.31
1965 -0.61 -0.25 0.03 0.01 0.50 0.86 1.14 1.66 1.84 2.06 2.03 1.81
1964 1.06 0.68 0.10 -0.42 -0.67 -0.64 -0.43 -0.72 -0.84 -0.73 -0.82 -0.92
1963 -0.50 -0.23 0.26 0.41 0.14 0.39 1.02 1.17 1.23 1.26 1.39 1.47
1962 -0.30 -0.26 -0.11 -0.24 -0.44 -0.14 -0.00 0.02 -0.23 -0.12 -0.32 -0.47
1961 -0.04 0.10 0.02 -0.00 0.26 0.44 0.11 -0.12 -0.38 -0.38 -0.01 -0.16
1960 -0.07 -0.22 -0.02 0.03 0.08 -0.06 0.07 0.36 0.28 0.18 0.15 0.04
1959 0.74 0.67 0.46 0.42 0.10 0.07 -0.37 -0.24 -0.23 0.20 -0.06 0.00
1958 1.98 1.72 1.26 0.81 0.71 0.69 0.51 0.52 0.25 0.41 0.65 0.44
1957 -0.29 0.02 0.45 0.77 0.94 1.05 1.34 1.36 1.27 1.37 1.52 1.71
1956 -0.99 -0.74 -0.54 -0.60 -0.46 -0.48 -0.58 -0.65 -0.43 -0.29 -0.54 -0.47
1955 -0.56 -0.57 -0.72 -0.78 -0.91 -0.67 -0.58 -0.80 -0.87 -1.60 -1.81 -1.61
1954 0.80 0.64 -0.04 -0.74 -0.45 -0.42 -0.62 -0.88 -1.03 -0.78 -0.50 -0.91
1953 0.56 0.61 0.62 0.64 0.71 0.90 0.70 0.63 0.85 0.86 0.82 0.83
1952 0.49 0.37 0.24 0.42 0.23 -0.03 -0.20 -0.00 0.21 0.25 -0.14 0.03
1951 -0.92 -0.66 -0.04 0.20 0.37 0.52 0.87 0.71 1.08 1.19 1.19 0.74
1950 -1.62 -1.32 -1.07 -1.11 -1.37 -0.74 -0.44 -0.42 -0.41 -0.32 -0.60 -0.88