11:40 AM | El Nino should completely reverse in a year or so

[Current SST anomalies with El Nino region circled; data courtesy NOAA, map courtesy "tropicaltidbits.com"]

Overview

El Nino conditions developed last year in the equatorial part of the Pacific Ocean and they have intensified significantly in the past several months. In fact, it appears that this El Nino will end up rivaling in strength the comparable events of 1972-1973, 1982-1983 and 1997-1998. This type of natural phenomenon features warmer-than-normal sea surface temperatures in the tropical Pacific Ocean while its counterpart called La Nina is associated with colder-than-normal waters. Given the fact that the Pacific Ocean is by far the world’s largest, it is not surprising that an El Nino of this magnitude is having major ramifications around the world and it will continue to do so for the next several months. Indeed, this El Nino is quite likely to play an important role in the upcoming winter around here in the Mid-Atlantic region: http://vencoreweather.com/2015/10/14/400-pm-2015-2016-winter-outlook-for-the-mid-atlantic-region/. There are some indications that the peak of this current El Nino episode will occur over the next month or two and then it’ll begin to weaken during the early part of 2016. In fact, there are some computer model forecasts that suggest this strong El Nino will completely reverse in a year or so to strong La Nina conditions and this too would have significant consequences around the world.

SST Anomalies

In the past few months, warmer-than-normal sea surface temperature anomalies (circled orange area in above plot) have spread westward from the west coast of South America into the central equatorial Pacific Ocean. Computer forecast models are in general agreement that this strengthening trend in the El Nino will reach its peak over the next couple of months and then there will be weakening next year. The effects of the current strong El Nino have already been appearing in numerous ways around the world. To begin, the added warmth to the sea surface temperatures in the Pacific Ocean has helped to fuel a very active tropical season in that part of the world. In addition, the Atlantic Basin has actually experienced a below-normal tropical season which is often the result of an El Nino as it tends to increase wind shear across the tropical Atlantic Ocean which, in turn, inhibits tropical storm formation.

Global temperatures

In addition to its impact on tropical storm activity, El Nino tends to generate a spike in global temperatures. The plot below of global temperature anomalies is produced by NOAA’s CFSv2 model and the circled areas show the spikes in global temperatures associated with recent El Nino events of 2006-2007 and 2009-2010 as well as the jump caused by the current episode. The spike associated with the current El Nino may continue for the next several months as there is often a lag in the effects of El Nino well past the actual peak in sea surface temperature anomalies. In other words, even if El Nino begins to weaken during early 2016, a residual “warming” effect can still show up for awhile with respect to global temperature anomalies. One other important point to make regarding the global temperature anomaly pattern that is related to El Nino is that in each of the recent El Nino events of 2006-2007 and 2009-2010, global temperatures dropped sharply in subsequent months following the El Nino.

[NOAA CFSv2 global temperature anomalies; courtesy Ryan Maue of Weather Bell Analytics]

Strong La Nina may be just a year away

Some computer forecast models are already predicting the demise of the current El Nino and, in fact, suggest a strong La Nina (colder-than-normal SSTs) will replace it by the end of next year. The plot below is a computer model forecast map from the Scripps Institution of Oceanography and it predicts there will be a strong La Nina event in a year or so in the same tropical region of the Pacific Ocean that is now experiencing well above-normal SSTs. As has been the case with the recent two El Nino events, a reversal like this would quite likely have serious ramifications on global temperatures. It would not be surprising to see another sharp drop in global temperatures once the current strong El Nino event fades away and La Nina conditions return to the tropical Pacific Ocean.

[Scripps Institution of Oceanography forecast map of tropical Pacific Ocean SST anomalies during late 2016 (greens, blues are colder-than-normal water temperatures]

Paul Dorian

Vencore, Inc.

Valley Forge, PA