Important Milestone: The El Nino Has Hit Its Peak Early

The very strong El Nino appears to have hit its peak earlier than predicted a few months ago, suggesting a substantial weakening later this autumn and winter.

Let's begin by looking at the sea surface temperature differences from normal (called anomalies) for two critically important areas in the central tropical Pacific:  the Nino 3.4 and 4 areas (see map below).

The magnitude of El Nino events is usually judged by the sea surface temperature anomaly in the Nino 3.4 area... and I show the latest values below (from NOAA Climate Prediction Center).  The magnitude of this El Nino appears to have leveled off over the last few weeks, around 2.5 °C above normal.

The fact that the sea surface temperatures are pretty much unchanged during the past few weeks is illustrated by the sea surface temperature anomalies on October 1 and October 19 (see below).

Hardly changed.

 

To understand the future of an El Niño event, it is useful to look at the upstream region (Nino 4) to gain insight into the future evolution of temperature in the Nino 3.4 region during subsequent months.

Why look upstream?   Because the sea surface warming tends to move eastward with the Kelvin waves I described in my previous blog.

The Nino 4 temperature anomalies (from climatological conditions) are shown below.   The Nino 4 temperatures rose rapidly from April to late June and then declined rapidly in July and August.

This is consistent with the rapid rise in Nino 3.4 temperature a few months later, from July through September.

NOAA runs complex atmosphere/ocean models for seasonal prediction.  NOAA's primary model  (the CFSv2) is predicting a rapid decline in the temperature in the Nino 3.4 area starting right now!   

If that prediction is correct, it means we are now at the El Nino peak.

Other modeling systems are less rapid in the decline, such as the GFDL Spear system (see below), but all suggest we are near the maximum. 

In summary, it appears that we are now at the peak of the current El Nino, and the latest forecasts are suggesting a fairly rapid decline.   

However, there is a lot of uncertainty in such forecasts because of the highly convective (e.g., thunderstorm) nature of tropical meteorology, and because the interaction between the ocean and atmosphere is often poorly modeled.

Lots to keep graduate students busy over the next decade!

The implications of the upcoming decline in El Nino will be the topic of a future blog.