A key monthly indicator for El Niño has reached a level not seen since 1997, according to the U.S. weather agency, when the weather pattern caused heavy rains and flooding in parts of South America and severe drought hit crops in Indonesia.

El Niño, the « little boy, » is driven by warm surface water in the eastern Pacific Ocean and its strength is measured by how much higher temperatures are over three-month averages.

In November, temperatures in the Niño 3.4 region, the central band of affected ocean running either side of the equator from 5S-5N and 170-120W, were 2.34 degrees Celsius above average, the National Oceanic and Atmospheric Administration (NOAA) said on its website.

That was the highest reading for the data that goes back to 1950 and a touch more than the 2.32 degrees Celsius recorded in November 1997 – a difference that NOAA considers statistically insignificant.

The Niño 3.4 value is the basis for three-month averages used in the Oceanic Niño Index (ONI) — one of the indicators that helps give historical context to the weather disruptions.

Temperatures in the Niño 3.4 region had hit a weekly record of 3 degrees Celsius above average in the week ending Nov. 16, in data that goes back to 1990.

The ONI for September, October and November 2015 is 2.04 degrees Celsius, Mike Halpert, deputy director of NOAA’s Climate Prediction Center, said in an email to Reuters. That is slightly behind the 2.18 degrees Celsius for the same period of 1997.

El Niño, which reaches a peak between October and January and persists into the first quarter, is eventually ranked by the peak of the ONI.

Japan weather forecaster says El Nino phenomenon is at its peak

03/12 – http://www.reuters.com