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Monsoon 2021: ENSO signs cooling of Pacific, IOD remains defiant, progressive Monsoon with adequate rains ahead

August 1, 2021 5:54 PM |

Monsoon 2021

The El-Nino – Southern Oscillation (ENSO) is currently neutral. Equatorial Sea Surface Temperatures (SST’s) are near to below average across most of the Pacific Ocean.

La Nina

In the last week, SST anomalies in the Central and East Central Pacific Ocean decreased. There is a significant drop over Nino 3.4 region marked over the deep oceanic surface. Also, there is noticeable rise over Nino 1+2 region, which is closer to the coastline.


ENSO neutral is favored through the Northern Hemispheric summer and in to the fall. Large probability is building for La Nina tentatively emerging through the Sep-Oct season and then lasting through the 2021-22 winters. El Nino threat is negligible and La Nina & Neutral conditions have equitable share during August and September. Overall ENSO continue to display progressive monsoon with adequate rains in the 2nd half of the season.

Indian Ocean Dipole (IOD)


The latest weekly value of IOD index to 25thJuly was -0.88°C. The IOD has been below the negative IOD threshold (-0.4°C) since onset of monsoon. By the end of July, the IOD values stabilize and forecast is reliable. Most of the numerical models anticipate the IOD index to remain -ve but limited to -1°C. This also means that IOD will not extend any support for enhancement of monsoon rains and will sit on the fence to allow ENSO drive the season.

Madden Julian Oscillation (MJO)


MJO is currently over West Pacific enhancing tropical storm activity. Three cyclones emerged simultaneously over the South China Sea : Cempaka, In-Fa and Nepartak. It is entering Indian Ocean after 03rdAugust, albeit with a decreased amplitude. Accordingly, monsoon may encounter weak phase in the 1sthalf of August as it happened in July also. Waxing and waning of intensity of monsoon is a very common feature and weak phase, if any, ostensibly recovers with fresh monsoon system over the Bay of Bengal.

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