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La Nina Is Weakening, IOD Remains Cold Neutral

February 11, 2023 5:34 PM |

La Nina is continuing in the tropical Pacific Ocean. Softening of La Nina is quite evident in the east and central Pacific, as the ocean surface has started warming. However, an appropriate atmospheric response is still awaited. 

ENSO:  Fading of La Nina is expected to make way for an evolving El Nino during Indian Summer Monsoon. El Nino is the warm phase of eastern and central Pacific vis-a-vis cooler and drier western Pacific. Warm equatorial water flows down the west coast of South America, depicting El Nino conditions. Such conditions typically persist for 9-12 months and rarely one sees back to back El Nino years. El Nino events tend to develop during the period Apr-Jun and invariably reach their peak strength during Oct-Feb. 

El Nino plot for the next 9 months suggest 2023 to be a devolving La Nina and evolving El Nino year. During the past 4 weeks, -ve SST anomalies have gradually weakened across most of the equatorial Pacific Ocean. Closer to the coast, Nino 1+2 index has already breached 0 degree mark to become warm neutral.  Commonly, Nino 3.4 warms up early and the heat travels to Nino 1+2. So change in the sea surface temperatures are defying the norms. Wait and watch situation prevails. This could may as well be early signs of 'Canonic' El Nino. 

El Nino plot is finding similarity with 2018, which also had the distinction of being a devolving La Nina and evolving El Nino year. Incidentally, monsoon 2018 ended with below normal and was just on the brink of mild drought. 

IOD :  The Indian Ocean Dipole is currently neutral.  The index is within the neutral bounds since Nov 2022. For the last 4 weeks, it is holding very close to cold neutral. The latest IOD index value for the week ending 05 Jan 2023 was -0.11deg.

Sea Surface Temperatures(SST's) are generally close to average across most of the tropical Indian Ocean.  Role of IOD becomes very significant just before and during the Indian monsoon. It holds the key for overall performance, specially during an evolving El Nino year. 

MJO  :  Madden Julian Oscillation is propagating eastward from Maritime continent in phase 4 to the Western Pacific. It is shrinking in amplitude during the 2nd week. MJO is constructively interacting with La Nina  and its evolution is favourable  for tropical cyclone activity, off Australian continent. 

Earlier, cyclone 'Freddy' formed northwest of Australia and  is sailing away from the landmass, posing no threat to the country. Another tropical storm 'Gabrielle',  Cat-I equivalent hurricane , is skirting the northeast coast of Australia and is likely to fizzle out over the open ocean waters. 

El Nino episodes, irrespective of 'evolving' or 'standard', usually result in spoiling Indian Monsoon. Rainfall over South Asia and Southeast Asia covering India, Malaysia, Indonesia, Thailand, Cambodia and West Pacific ring countries bear the risk of deficient rains during monsoon season. 

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