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9:15 AM | Strengthening El Nino in the tropical Pacific Ocean to have global ramifications

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Weather forecasting and analysis, space and historic events, climate information

9:15 AM | Strengthening El Nino in the tropical Pacific Ocean to have global ramifications

Paul Dorian

SST-Anom-changes.png

Discussion

Overview

El Nino conditions began to develop last year in the equatorial tropical Pacific Ocean and all indications suggest rapid strengthening is now taking place. This type of natural phenomenon features warmer-than-normal sea surface temperatures in the tropical Pacific Ocean with its counterpart, La Nina, associated with colder-than-normal waters. Given the fact that the Pacific is by far the world’s largest ocean, an El Nino in its equatorial region can have significant ramifications on weather and climate in many parts of the world; especially, one that is strengthening rapidly and sustained.

In the past 30 days, sea surface temperature anomalies have changed noticeably off the west coast of South America as rapid warming has taken place (orange area in comparison map above). Computer forecast models are in general agreement that this strengthening trend will continue for the next few months perhaps followed by weakening in the overall El Nino later this year.

Ramifications of a strengthening El Nino

The tropical Pacific Ocean is perhaps the most important part of any ocean across the world and strengthening El Nino conditions can have the following ramifications around the globe:

1) An El Nino during the summertime typically results in below-normal activity in the tropical Atlantic Ocean as it tends to generate stronger-than-normal upper level winds which act to suppress "African-wave" storm development.

2) An El Nino during the summertime typically results in normal-to-cooler-than normal temperatures across the Midwest and Northeast US.

[Note – both items 1 and 2 are described in detail in Vencore Weather’s 2015 Tropical Outlook: http://vencoreweather.com/2015/05/05/1000-am-2015-tropical-and-mid-atlantic-summertime-outlooks/]

3) An El Nino is likely to result in more rainfall compared to normal in the Southwest US which could alleviate drought conditions in California during the next 6-12 months or so.

Nino_index_values_2005-20151.png

[Oceanic Nino Index (ONI) values for past 10 years (red=El Nino, blue=La Nina, black=neutral); courtesy NOAA]

4) Finally, an El Nino is likely to cause a spike in global temperatures. The table above lists the monthly “Oceanic Nino Index” for the past 10 years and there have been two El Nino episodes (arrow regions) in which an (red) index value of 1.0 was reached (moderate strength): "late 2006" and "late 2009 into early 2010". While I do not believe this El Nino will develop to "super" strong levels (i.e., index values of 2.5 or higher), I do believe it will strengthen to strong levels (i.e., 1.5 to 1.9) during the next few months from its current reading of 0.6 before weakening likely begins late in the year or early in 2016.

While there has been a jagged, and generally downward trend in global temperatures during the past 10 years according to NOAA's CFSR/CVSv2 data, in those months associated with these two El Nino episodes global temperatures actually spiked. The circled areas in the plot below show the “El Nino-induced” spikes in global temperatures associated with the "late 2006" and "late 2009/early 2010" moderate-strength El Nino events (data courtesy Ryan Maue at Weather Bell Analytics, NOAA). In addition, an important point to note is that in both of these El Nino events, global temperatures actually dropped sharply shortly after El Nino conditions subsided (circled regions).

global_temps_2005_thru_31DEC2014_with_El_Nino_spikes.png

[Global temperature anomalies from 2005 through 2014 using NOAA's CFSR/CVSv2 data; courtesy Ryan Maue at Weather Bell Analytics, weatherbell.com]