Severe Thunderstorms and Excessive Rainfall in the Mid-Atlantic; Heat and Fire Weather Concerns in the West

Scattered strong to severe storms, excessive rainfall, and flooding are expected across parts of the Mid-Atlantic into the Northeast today. Flood Watches are in effect. Heat will continue to impact the West today. Heat advisories are in effect for portions of the Intermountain West; and Extreme Heat Warnings are in effect for portions of Arizona and southeast California. 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

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