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Pacific Ocean Triad: La Nina Ends, ENSO Turns Neutral, El Nino Watch Begins

March 18, 2023 6:12 PM |

Monsoon 2023

Triple Dip La Nina has finally rested in the Pacific Ocean. Equatorial Pacific as such was warming since mid-February. However, atmospheric indicators were slow in responding. Now, the synchronization of both beacons has ended the longest run of La Nina since 2000. The El Nino- Southern Oscillation(ENSO) has turned neutral.  Concurrently, the Bureau of Meteorology -Australia and Jamstec (Japan) have issued El Nino 'WATCH' in their latest outlook. This 'Watch' is a bulletin indicating favourable conditions for the development of El Nino with a notice period of 6 months.  An El Nino watch is not a guarantee that El Nino will occur and it is rather an indication that few typical precursors are turning promising for the event.

The Climate Prediction Center (CPC) as part of the National Oceanic and Atmospheric Administration's (NOAA) National Weather Service in the USA is yet to announce this caution. El Nino is a global phenomenon and a lot of international agencies closely follow its development and progress. CPC is one such reputed institution which monitors El Nino right from inception, till termination and issues bulletins for El Nino Watch, El Nino Advisory and Final El Nino Advisory.

ENSO: There is no absolute consensus amongst the numerical models for the complete cessation of La Nina and the commencement of El Nino. The objective model-based forecast supports the dissipation of La Nina and the initiation of El Nino on account of surface and sub-surface warming of the equatorial Pacific. During the last 4 weeks, negative Sea Surface Temperature(SST) anomalies weakened across most of the equatorial Pacific Ocean. Positive SST anomalies have surfaced and built up noticeably in the eastern Pacific.

SST anomalies

The principal measure for monitoring, assessing and predicting ENSO remains with Oceanic Nino Index (ONI), which is primarily derived from the SST departure from the average in the Nino 3.4 region.

Nino Indices

ONI is slightly 'cold neutral' and seems to be sitting on the fence to crossing over to 'warm neutral' very soon. El Nino is characterized by +ve ONI >/= 0.5 degree Celsius. For declaring El Nino, these thresholds must be exceeded for a period of at least 5 consecutive overlapping 3 months of the season.

ENSO Probabilities

IOD: The Indian Ocean Dipole is neutral. The reliability of the IOD forecast at this point in time is just about 4-6 weeks. It will be rather too early to read too much from the current model projections for the monsoon months.

Indian Ocean Dipole

The IOD index value for the week ending 12 March 2023 was +0.19 degrees which are within the neutral bounds of +/- 0.4 degrees.

Indian Ocean Dipole

The fluctuation in the index value over the last 4 weeks goes on to speak of its volatility at this point in time.

Indian Ocean Dipole

MJO: Madden Julian Oscillation had strengthened during 1st half of March. It got support from interaction with La Nina. Currently, it is in phase 8 with a fairly large amplitude. A steady decline is likely in the signal strength as it propagates eastward. La Nina has ended and the Pacific has turned ENSO neutral. The further eastward movement of MJO is likely to be slow as it enters phases 1 & 2 over the equatorial Indian Ocean. Also, the amplitude will be shrinking and get confined to the minimal value in the inner ring. No major support is expected on account of MJO for any perturbation in the Indian Seas till fag end of March.

Madden Julian Oscillation

Southwest monsoon 2023 will get going under the shadow of an evolving El Nino. Although, the performance of seasonal forecast models is considered low, at this time of the year, due to the 'spring predictability barrier', the persistent pattern emerging in the equatorial Pacific does indicate likely formation of a full-fledged El Nino during the later half of Indian Summer Monsoon. El Nino invariably corrupts the bursts of monsoon and therefore, an aberration of seasonal rainfall is highly probable.

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