El Nino Status on 7th April 2015
Full fledged EL Nino was confirmed only at the end of March 2015 when the five consecutive 3 monthly seasons had ONI index of 0.5 C or higher. Incidentally it has barely made it to a full fledged El nino. The March SST for Nino 3-4 region is 27.72 C. If however, this SST was a wee bit lower at 27.68 C ( a difference of 0.04 C only), the ONI Index for JFM would have been 0.4 C and the El Nino would have gone bust (the fifth consecutive 3 monthly season would not have qualified for El Nino).
The above points to be kept in mind and since ONI is always reported with only one decimal, yes we have an El Nino !!!
As per NOAA Officially El Nino is declared as per conditions laid down and shown in ONI Index graph below:
El Niño: characterized by a positive ONI greater than or equal to +0.5ºC. La Niña: characterized by a negative ONI less than or equal to -0.5ºC. By historical standards, to be classified as a full-fledged El Niño or La Niña episode, these thresholds must be exceeded for a period of at least 5 consecutive overlapping 3-month seasons.
Most of the agencies monitoring El Nino had been forecasting every month from the first quarter of 2014 that an El Nino would begin in the next two months. The year 2014 has completed without a full fledged El Nino. Only two consecutive overlapping 3-month seasons SON and OND have had ONI index equal to or above +0.5ºC thresh hold till end of 2014. SON 2014= +0.5ºC and OND 2014 = +0.7ºC
The first two months of 2015 had two more overlapping 3-month season NDJ & DJF with ONI index equal to or above +0.5ºC thresh hold. NDJ 2015 ONI=0.7ºC & DJF 2015 ONI= 0.6ºC. The recent 3- month season the ONI index for JFM =0.5ºC. This makes total of five consecutive overlapping 3-month seasons SON 2014, OND 2014, NDJ 2015, DJF 2015 & JFM 2015 with ONI index equal to or above +0.5ºC thresh hold till end of March 2015. The respective ONI Index are SON 2014= +0.5ºC and OND 2014 = +0.7ºC, NDJ 2015=0.7ºC, DJF 2015=0.6ºC & JFM 2015=0.5ºC.
CPC had issued an El Nino Advisory on 5th March 2015 in anticipation that JFM 2015 ONI would be 0.5ºC or more.
CPC considers El Niño or La Niña conditions to occur when the monthly Niño3.4 OISST departures meet or exceed +/- 0.5°C along with consistent atmospheric features. These anomalies must also be forecasted to persist for 3 consecutive months.
The atmospheric features justify the declaration of El nino because SOI was -10.7 as per BOM.
Southern Oscillation Index
The Southern Oscillation Index (SOI) has moved to negative zone from neutral zone during March 2015. The latest 30-day SOI value from BOM-Australian Government for period ending 29 March is −10.71 which denotes negative zone.
SOI Monthly graph till end of March 2015 – The Long Paddock – Queensland Government
This El Nino though weak at present is the only El Nino to have been declared as full fledged El nino at the end of March in any year from 1950 on wards.