The exceptionally warm waters of the tropical Pacific Ocean have surpassed yet another milestone, pushing this El Niño one step closer to becoming the strongest on record.
The strength of El Niño is measured by how abnormally warm the ocean water is in the equatorial Pacific. There are many zones in the Pacific that are used to quantify the strength of an El Niño, including the often-cited Niño 3.4 zone. Ocean surface temperature is measured and averaged over the entire region in periods of a week, a month and three months. The records in this region are typically broken by fractions of degrees.
In mid-November, the Niño 3.4 region set a new record for weekly temperature — 3 degrees Celsius, or 5.4 degrees Fahrenheit, above average. It was the highest temperature departure ever recorded in the region on the scale of one week.
Now the data for the entire month of November are in, and it eked out November 1997, the previous record-high, by 0.02 degrees Celsius. It is not a huge margin, but a remarkable achievement nonetheless against what is remembered as the most intense, most influential El Niño since records began in 1950.
The next hurdle this El Niño would need to overcome is a record for three-month average temperature. This final metric is what NOAA tends to cite when referring to historic El Niño and La Niña events.
The average for September, October and November came in at 2.0 degrees warmer than average. This is 0.2 degrees cooler for the same period in 1997, but we could see this year’s El Niño peak later than the 1997-1998 event, so the October-November-December and November-December-January reports will be the ones to watch.
More important than the metrics, though, are the global weather effects. El Niño can have a significant influence on weather patterns, particularly in North America during the winter. Strong El Niños coincide with a high likelihood for high pressure to build over a huge portion of the continent — including the eastern United States — while cool troughs of low pressure tend to dominate the eastern Pacific Ocean and West Coast, and skirt east across the southern states.
We have already seen this pattern take shape across the United States this fall — with temperatures running much warmer than average across the eastern United States — and we expect it to strengthen in December.
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