El Nino is a climatic pattern in which warming waters of the central and eastern Pacific Ocean have significant impact on global weather. Equatorial sea surface temperatures (SST’s) in the Pacific transitioned from below- average to above-average in Jan 2023. Since March 2023, positive SST anomalies in the eastern Pacific Ocean expanded westward. These anomalies have strengthened over the last 6 months. Pacific Ocean had responded quite early to the call of El Nino, and now atmosphere also got aligned to evolve perfect ENSO.
ENSO: For the El Nino event, the surface temperature anomalies in the Nino region need to breach the threshold mark of +0.5°C for longer duration. More steep is the rise, stronger is the degree of El Nino. Given the recent trend in the Pacific, the degree of confidence for a stronger El Nino event looks imminent during fall of the year. The anomaly may reach or exceed 1.5°C from the seasonal average in the Nino 3.4 region. NOAA has announced that the chances of El Nino event this season has increased to 95% and with greater confidence in a ‘strong’ El Nino event.
Nino region is segregated in to 4 zones as mentioned above in the table. SST anomalies have far exceeded the threshold mark across all regions. Very pertinent to note that in addition to the anomalies, the location of warmest pocket need to be carefully ascertained. Currently, an explosive warming has been noticed in Nino 1+2 region, next to the South American coast, since early July 2023. It looks like an eastern-driven El Nino cycle so far. Such conditions resemble ‘Canonic’ El Nino, when the eastern Pacific Ocean gets warmer, more than the central and western Pacific. Occasionally, when the El Nino is full blown, the west and central Pacific may even observe negative SST anomalies during Canonic El Nino. Data is rather sparse of such events and therefore the findings remain inconclusive. In the recent history, year 2014 was ‘Canonic’ El Nino and a drought year for Indian monsoon.
IOD: Indian Ocean Dipole is currently neutral. The IOD index for the week ending 13Aug 2023 was +0.32°C, which is within the neutral bounds ( between -0.4°C and +0.4°C). The index has been slithering for the last few weeks but unable to breach the threshold mark. In the last 5 weeks, the index has risen from 0.0°C to +0.32°C. It is still ricketing and not good enough to take on the blues of El Nino. The climate models do suggest a positive IOD event in the coming weeks, but the mismatch between the model output and the actual value is discernible. IOD need to be rising steeply to break the shackles of Pacific warming.
MJO: Madden Julian Oscillation is a global scale feature of the tropical atmosphere. It is also the major fluctuation in the tropical weather on weekly to monthly time scale. MJO effects are most evident over the Indian Ocean and Western Pacific Ocean. It influences largely the typhoon activity over Western Pacific and hurricane development in the Eastern Pacific. It also influences the formation of monsoon systems over the Indian Seas. It can steer the monsoon pattern to bring intra seasonal variability. The Madden Julian Oscillation is in the Western Hemisphere with a slight increase in the amplitude. Few models are forecasting moderately strong MJO pulse over the Pacific Ocean in the coming weeks. This may possibly assist further strengthening of El Nino conditions.
Seasonal rainfall has succumbed to the impact of El Nino in core monsoon month of August. El Nino is casting shadow to corrupt the monsoon bursts. Month of August has witnessed unprecedented shortfall of nearly 40% rainfall so far. Marginal recovery is likely in the 3rd week but still not adequate enough to offset regional deficiencies.