Typical El Nino conditions developed in the Tropical Pacific for the first time in 7 years. This had set the stage for rise in temperature globally, disruption of weather and chaotic climate pattern. Prior to this, El Nino conditions came up, post southwest monsoon in 2015 and developed early before commencement of monsoon in 2019. On two of the earlier occasions, El Nino had appeared after a gap of 5-6 years in 2009 and 2015.
The onset of El Nino enhances the likelihood of breaking temperature records and increasing extreme weather events. July and August this year are considered the warmest. With four months still to go, 2023 may go on record for extreme heat and adverse weather occurrences. The announcement of El Nino itself is enough to mobilize preparation and anticipatory action, to contain the ill effects of this unsparing phenomenon.
ENSO: Transition from the below average to warmer than average sea surface temperature in the tropical Pacific commenced in January 2023. Since March 2023, positive SST anomalies in the eastern Pacific Ocean have expanded westward. In the last 4 weeks, equatorial SSTs were above average, in excess of 1°C, across all the Nino regions.
In addition to Nino 1+2, which witnessed explosive warming , Nino 3 also getting aligned and the warmth is expected to expand further to Nino 3.4 region. The Southern Oscillation Index (SOI), an indicator of the air pressure of the overlying atmosphere over the Nino region is increasingly becoming negative. The latest mean value for August 2023 was -0.8°C. Although, the exact initiating causes of an ENSO warm or cool event are not fully understood, but the two components of ENSO – sea surface temperature and atmospheric pressure are strongly related.
IOD: The Indian Ocean Dipole index for the week ending 03 Sep 2023 was +1.05°C. This is the 3rd successive week having +VE IOD. The index value has increased significantly from +0.79°C to +1.05°C. Numerical models indicate further increase till November 2023. Several more weeks of positive IOD values are needed to list a +VE IOD event. A record positive IOD occurred nearly 4 years ago, in monsoon 2019. The IOD index exceeded 2°C during the monsoon season. September 2019 ended with a surplus of 53% rainfall, the highest ever in the last 100 years.
MJO: Increasing El Nino influence is interacting with Madden Julian Oscillation activity. Models depict a quasi-stationary MJO signal over the Maritime Continent, in close proximity to the Indian Ocean. MJO amplitude is getting restricted during further eastward propagation. Enhanced convection is favoured over the Western Pacific and Indian Seas (Bay of Bengal) over the next week. There are a fair amount of chances for the development of tropical cyclones in the Western Pacific and the Philippines Sea. MJO may not enhance monsoon activity effectively over the Bay of Bengal, but it is not going to suppress the surge, as such. More or less, it may play neutral. There is consensus among the dynamical models for the diminishing of MJO amplitude during the latter half of September.
MJO pulse is likely to move over the Maritime Continent or Western Pacific in the coming days. Even a moderate amplitude of MJO will assist the strengthening of El Nino, by weakening trade winds. El Nino will be up against the combined influence of positive IOD and marginally favourable MJO, during the week starting 11 September 2023.