September 2020 Is Hottest Ever Recorded, Here Comes La Niña

Graphic: NOAA

The National Oceanic and Atmospheric Administration (NOAA) announced yesterday that September 2020 was the hottest month of September ever recorded and that they now fully expect that 2020 will be one of the three hottest years on record.  According to The Hill, “September 2020 was 1.75 degrees Fahrenheit hotter than the 20th-century average of 59 degrees Fahrenheit, and 0.04 degrees hotter than the two next-warmest Septembers of 2015 and 2016.”  And this is part of a string of warm Septembers — the last 7 years have been the warmest 7 ever, and the 10 warmest Septembers have all occurred since 2005.

Why This Matters:  Every month for the last 429, global temperatures have been “at least nominally” above the 20th-century average — so it’s not just Septembers that are warm.  This is really not the kind of above-average we can celebrate.  Meanwhile, we are heading into a “strong” La Niña, according to NOAA and that will exacerbate and extend the warm, dry weather that has been devastating to the Southwestern and Western U.S.  Indeed, the LA Times reported that Arizona and California experienced their warmest April-to-September period in 126 years, the Drought Monitor reported. New Mexico and Nevada had their second-warmest such period. At the same time, the northern tier of the country is likely to see a cold, wet winter in a typical La Niña.

More Climate Stats

NOAA also reported a couple of other key statistics.

  • “Arctic sea ice was at near-record lows: Average Arctic sea ice coverage (extent) for September ranked second smallest on record. On September 15, sea ice covered just 1.44 million square miles of the Arctic, the second-smallest minimum extent on record behind September 17, 2012. The 14 smallest minimum annual extents have occurred in the last 14 years.”
  • “A record-hot YTD so far for some: Europe, Asia and the Gulf of Mexico had their warmest January-through-September period on record; South America and the Caribbean region had their second highest. No land or ocean areas had record-cold YTD temperatures.”
  • The year-to-date (YTD) average global temperature was the second hottest on record at 1.84 degrees F (1.02 degrees C) above the 20th-century average. This is only 0.07 of a degree F (0.04 of a degree C) shy of the record set for the same YTD in 2016.”
  • The Northern Hemisphere’s YTD temperature tied with 2016 as the hottest on record, while the Southern Hemisphere saw its fourth hottest YTD.”

What’s A La Niña?

According to NOAA, a La Niña exists when the sea surface temperatures in the central and eastern equatorial Pacific are below average. That causes easterly winds over that region to strengthen, and rainfall usually decreases over the central and eastern tropical Pacific and increases over the western Pacific, Indonesia, and the Philippines. These impacts in turn affect the weather in the U.S.  The LA Times reported that NOAA said last Thursday that “La Niña conditions in the tropical Pacific continue to develop, and forecasters now are expecting a stronger La Niña with about an 85% chance of it persisting through the winter.”

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