National Weather Service United States Department of Commerce

Tropical Storm Colin Pulls Away from the Coast; Severe Weather for Portions of Montana and Plains on Sunday

Tropical Storm Colin will continue to track away from the U.S. East Coast through Sunday. Meanwhile, severe weather potential for portions of Montana and the Plains are forecast through Sunday. Critical fire weather conditions to persist across the Great Basin and interior Alaska the remainder of the weekend. Heat will build for the Plains, Ohio and Tennessee Valleys and Great Lakes into Monday. Read More >

ENSO Indices


ENSO Regions


Southern Oscillation Index (SOI)
standardized anomaly of the mean sea level pressure difference between Tahiti and Darwin

  • traditional ENSO index

  • correlates strongly with SST anomaly indices

NOAA Oceanic Niño Index (ONI)
sea surface temperature anomaly index for Niño 3.4 (5°N to 5°S, 170°W to 120°W)

  • onset of El Niño declared when Niño 3.4 anomaly exceeds +0.5°C for 3-month period

  • to be "full-fledged" El Niño (or La Niña), onset conditions must be met for 5 consecutive 3-month periods

Japanese Meteorological Agency ENSO Index (JMA)
sea surface temperature anomaly index for Niño 3 (4°N to 4°S, 150°W to 90°W)

  • less noisy than traditional SOI and more vigorous than NOAA ONI

  • anomalies must exceed 0.5°C for 6 consecutive 5-month periods

Multivariate ENSO Index (MEI)
weighted anomaly average of 6 meteorological variables in the tropical Pacific

  • sea surface temperature

  • sea level pressure

  • surface air temperature

  • components of surface wind

    • zonal component

    • meridional component

  • total cloudiness fraction of the sky