This month’s ENSO Climate Update is provided by Climate.gov and written by Michelle L’Heureux on April 9, 2020.
Itās a new month, but it seems like an entirely different world as we peer at the tropical Pacific Ocean.Ā Ā Sea surface temperatures remained warmer than average, but the tropicalĀ atmosphere shifted away from its El NiƱo-ish appearance during February.Ā Ā The lack of coupling between the ocean and atmosphere leads forecasters to once againĀ favor the continuation of ENSO-neutral with a ~60% chance during the summer and remaining most likely during the autumn.
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In the last month, ocean surface temperatures in the NiƱo-3.4 region have been bubbling around +0.5Ā°C,Ā our El NiƱo threshold.Ā Ā If you look at monthly averages in this region going back to October 2019, weāve been between +0.45Ā°C and +0.50Ā°C forĀ five of the six months!Ā Ā Ā Thatās pretty special!
Itās special because there isnāt an analogous streak, remaining right atĀ +0.50Ā°C,Ā in theĀ historical recordĀ going back to 1950.Ā Ā However, keep in mind that right now the ādeparture from averageā is being computed relative to 1986-2015 seasonal averages.Ā Ā Eventually, becauseĀ we roll the climatology forward in time, the current numbers will change when we update the reference (averaging) period to 1991-2020.Ā Ā Because sea surface temperatures are above average over most of the Tropics right now, suggesting that the updated 30-year average will be warmer than the 1986-2015 average, we are betting these historical index values will eventually be revised downwards.
However, weĀ donāt just look at the ocean temperaturesĀ when we determine the status of ENSOāwe also examine the atmospheric circulation over the tropical Pacific Ocean.Ā Ā Changes in the atmospheric circulation (especially the location of tropical rainfall)Ā result in teleconnectionsĀ that impact the climate over far-flung regions across the globe.
Other thanĀ some evidence in February, we have not seen persistent shifts in tropical rainfall, and March 2020 was no exception.Ā Ā In the past month, rainfall/cloudiness was near average-to-suppressed in the central tropical Pacific Ocean (during El NiƱo, there isĀ typically increased rainfall/cloudinessĀ in this region).
Stronger-than-average trade winds were also observed over the central and eastern tropical Pacific Ocean, which is not typical of aĀ reduced Walker circulationĀ that would occur during El Nino. TheĀ Southern Oscillation indicesĀ remain near average as well.Ā Ā So, it appears the warm ocean is socially distant from its atmospheric dance partner.
Mute Your AudioĀ Ā
Model forecastsĀ continue to indicate that ENSO-neutral conditions will persist through Northern Hemisphere summer and into the autumn of 2020.Ā Ā Forecasters are keeping one eye on a possibleĀ La NiƱaĀ during the latter half of the year, which is reflected in theĀ 30-40% chances.Ā Ā The āin houseāĀ NCEP Climate Forecast SystemĀ (CFSv2) is one of the most bullish models to support development of La NiƱa, but there are many other state-of-the-art models that disagree, so forecasters are not putting much weight in it at this point.
With that said, the spread of possible outcomes is still considerable and we are smack dab in the midst of theĀ spring prediction barrier, which is when models tend to have lower skill or accuracy.Ā Ā Ā
Also, as Emily pointed outĀ last month, it would be unusual for a La NiƱa to form after an ENSO-neutral winter. But as regular readers know, with only a small number of historical ENSO events to compare to (20-25 El NiƱo or La NiƱa episodes since 1950), āunusualā is often the norm!Ā Ā All the more reason to keep watching ENSOāeach event or non-event is a learning experience.
Thatās the Way We Became the Brady BunchĀ
Weāre on the cusp of our 6th birthday on the blog, so by now you may be wondering who are the people who bring you these ENSO predictions every month.Ā Ā Our newly remote set up provided an opportunity for a group photo among the teamā¦ brains and brawn power these ENSO forecasts!
It is a privilege to work with such a talented bunch of scientists and communicators.Ā Even in these uncertain times, weāll continue to look ahead for you.Ā Ā Iām swapping with Emily (top left square) this month, so look for her blog post later this month and again early next month.Ā Ā Until then, stay safe and physically distant!