El Nino is a global phenomenon and a lot of international agencies closely follow its development and progress. Climate Prediction Center (CPC) is one such agency which monitors El Nino right from its initial indications to its end and issues the following advices-
El Nino Watch- The CPC issues a bulletin indicating conditions favourable for development of EL Nino and La Nina with a notice period of 6 months.
El Nino Advisory (presently in vogue)- It is issued when El Nino or La Nina are observed and expected to continue.
Final El Nino Advisory- This is issued when El Nino or La Nina conditions have ended.
What is an El Nino?
As have been reiterated by Skymet, El Nino is an abnormal warming of surface ocean waters in the equatorial Pacific, which occurs every two to five years. Such an event is characterized by occurrence of normal tropical storms and Hurricanes in Eastern Pacific and decrease in storms in the Atlantic, Gulf of Mexico and the Arabian Sea.
Higher temperature and lower pressure changes the wind pattern and impacts rainfall figures. According to G.P Sharma, of Skymet’s Meteorological Division, low rainfall during the Monsoon does not necessarily mean it's an El Nino year, but an El Nino year will invariably have below normal Monsoon rainfall in India.
It is believed that El Nino may have contributed to the 1993 Mississippi and 1995 California floods. It is also believed that El Nino contributed to the lack of serious storms such as hurricanes in the North Atlantic which spared states like Florida from serious storm related damage.
Therefore, this indicates that not all El Nino's are the same, nor does the atmosphere always react in the same way from one El-Nino to another.
El Nino affects Monsoon in India
El Nino is closely associated to Monsoon in India, which is often weaker during occurrence of such a phenomenon, although by no means always. 60% of all droughts in India in the last 130 years have been El Nino droughts.
In February, the situation seemed conducive for a poor Monsoon in India. And as we entered mid-April, these observations were turning out to be more accurate. Other meteorological agencies across the world also strongly pointed towards the likelihood of an El Nino weather pattern this year.
El Nino, meaning “little boy” in Spanish, leads to warming of sea surface temperature (SST) above 0.5oC. From the 21st to 25th of May, the surface temperature remained constantly at 0.6oC. This could be attributed to poor performance of Monsoon in India with rain deficiency at 43% till 12th of July.
Thereafter, conditions relaxed and rain deficiency came down to 22% by end of July as the surface temperature in the equatorial Pacific came down to 0oC and even further to -1 oC. However, as of now there seems to be a rising trend in temperatures across the Pacific Ocean.
Equatorial Pacific is divided into four parts Nino 3, Nino 4, Nino 3.4, Nino 1+ 2, for Meteorological analysis. Any occurrence over Nino 3.4 is most relevant for Monsoon in India.
Under the Tropical Ocean Global Atmosphere program (TOGA), a number of Buoyes or equipments are deployed between 7o N and 7o S Latitudes in the Pacific. These Buoyes placed in an array fashion, constantly records temperatures, which are further verified with satellite derived temperatures.
As reiterated by Skymet, El Nino is still evolving. As per latest updates by International Research Institute for Climate and Society (IRI) of Columbia University the chances of El Nino occurring this year now stand at 60%, peaking during winter in the Northern Hemisphere.
Here’s a look at the SST since August-
| Date (2014) | Nino 3 | Nino 4 | Nino 3.4 | Nino 1+ 2 |
| August 4 | 0.2oC | 0.3oC | - 0.1oC | 0.6oC |
| August 11 | 0.4oC | 0.5oC | 0.0oC | 1.2oC |
| August 18 | 0.5oC | 0.4oC | 0.0oC | 1.2oC |
| August 25 | 0.5oC | 0.4oC | 0.3oC | 1.4oC |
| September 2 | 0.4oC | 0.5oC | 0.4oC | 0.8oC |
| September 9 | 0.4oC | 0.5oC | 0.4oC | 1.2oC |
| September 16 | 0.4oC | 0.7oC | 0.5oC | 0.7oC |
Oceanic Nino Index (ONI)
The Oceanic Nino Index (ONI) is based on SST departures from average in the Nino 3.4 region. At present a positive equatorial SST anomalies continue across most parts of the Pacific Ocean.
While El Nino is characterized by a positive ONI greater than or equal to +0.5ºC, La Nina is characterized by a negative ONI less than or equal to -0.5ºC.
The figure below shows that in a three month period from June to August, the average temperature has always been positive during El Nino years (2002 and 2009). However, this year the temperature is 0.0, indicating a deflating or weak El Nino. The ONI has not inched towards the threshold value and El Nino will not be a strong one even if it peaks during winter months in the Norther Hemisphere.
Picture courtesy- CPL and Snowbrains