1:00 PM | El Nino has likely reached its peak intensity and will reverse to La Nina by later this year

The latest sea surface temperature anomalies showing El Nino region (circled); courtesy NOAA

Overview
In all likelihood, El Nino in the tropical Pacific Ocean reached its peak intensity level several weeks ago and will completely flip to La Nina conditions later this year.  This naturally occurring oceanic cycle that produces warmer-than-normal sea surface temperatures (SSTs) in the equatorial region of the Pacific Ocean began in earnest early last year and strengthened throughout 2015.  It has become comparable in strength to the very strong El Nino events of 1997-1998 and 1982-1983 although the warmest region relative-to-normal has set up in a different location (current El Nino "centrally-based", 1997-1998 "eastern-based").  While the demise of this current El Nino event has likely begun - make no mistake about it - there will still be significant ramifications for the next few months in many places around the globe.  By later this year, colder-than-normal sea surface temperatures are quite likely to appear in the tropical Pacific Ocean as suggested by numerous computer models and this flip to La Nina will also have widespread consequences.  

El Nino tropical Pacific Ocean region broken into smaller sections

Signs of weakening for El Nino
As a way of tracking temperature anomalies in different regions of the tropical Pacific Ocean, meteorologists have broken up the area into small sections as shown in the map (above).  In all four of these regions (Nino 4, Nino 3.4, Nino 3, Nino 1+2), the sea surface temperature anomalies dropped between November and December suggesting the peak intensity of this El Nino event has likely passed (red numbers in table below).  All indications are that this downward trend in sea surface temperature anomalies will continue over the next several months.  In fact, numerous computer models predict near neutral ENSO conditions by spring or early summer and then La Nina conditions by later this year.

Monthly temperature anomalies (in red) for 2015 in 4 El Nino regions; courtesy NOAA; Source of table: https://www.ncdc.noaa.gov/teleconnections/enso/indicators/sst.php

Model predictions of La Nina
Two computer forecast models are shown below showing a dramatic change in sea surface temperature anomalies in the tropical Pacific Ocean between now and late 2016.  The first comparison map shown comes from the Japan Meteorological Agency and depicts the SST anomalies from the current 3-month period of December/January/February and June/July/August.  The current warmer-than-normal SSTs in the tropical Pacific Ocean (red region) reverses to colder-than-normal (blue region) conditions by later this summer.  A second model generated by the Scripps Institute of Oceanography provides support to this flip as it too shows a dramatic change from El Nino conditions (yellow, orange) in the spring to La Nina (blue, green) conditions by the fall.

Sea surface temperature anomaly forecasts by Japan Meteorological Agency

Sea surface temperature anomaly forecasts by Scripps Institute of Oceanography

Continuing significant ramifications of El Nino
The current El Nino has had significant ramifications around the world and will continue to do so throughout the winter season despite its expected weakening over the next few months.  To begin, global temperatures have spiked in recent weeks as is quite typical during El Nino events; especially, those on the strong side.  Also typical of El Nino events and subsequent flips to La Nina, global temperatures will very likely drop sharply after the colder-than-normal sea surface temperatures appear in the tropical Pacific Ocean.,  In this case, look for this sharp drop in global temperatures late this year, or more likely, during 2017 and beyond.  

Second, in the Mid-Atlantic region this "centrally-based" El Nino will likely have a big impact over the next few months specifically in terms of activating the southern branch of the jet stream.  The result will quite likely be an overall relatively stormy pattern with potential coastal storms enhancing chances for some serious snowfall during the second half of winter (see Winter Outlook for more on that: http://www.vencoreweather.com/2015-2016-winter-outlook). .

Third, "El Nino enhanced" drought-busting storms will pound California during the next few months with significant rain along coastal sections and snow in interior higher elevation locations.  Once the El Nino ends and neutral-to-La Nina conditions take hold, expect a dry pattern to return to California for the late spring/summer.

Finally, the Atlantic Basin experienced below-normal tropical activity last year (actually for the last ten years) and this can be at least partially attributed to El Nino as it tends to increase wind shear across the tropical Atlantic Ocean which, in turn, inhibits tropical storm formation. Without this “benefit” of El Nino, it is quite likely that the 2016 Atlantic Basin tropical season will become much more active than last summer – more on that outlook later this year.  For more information on this El Nino event: https://nynjpaweather.com/public/2016/01/06/the-state-of-the-201516-el-nino/).  

Meteorologist Paul Dorian
Vencore, Inc.