El Niño has officially started and chances of it intensifying into one of the strongest ever have soared, according to a new update by U.S. scientists.

The National Oceanic and Atmospheric Administration (NOAA) has upgraded the U.S. El Niño status from "watch" to an "advisory," its monthly release, published on Thursday, said, with above-average sea surface temperatures across the central to eastern equatorial Pacific Ocean over the past month.

"There is a 63% chance of a very strong El Niño during November-January that would rank among the largest El Niño events in the historical record going back to 1950," it said. That is nearly double the odds the agency estimated in May.

El Niños are complex weather patterns known to fuel extreme weather conditions like droughts and floods. "Even very strong El Niño events do not lead to the expected impact everywhere, but stronger events can more significantly tilt the odds in favor of expected outcome," the NOAA update added.

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