Indian Ocean switches to positive dipole mode; strong monsoon seen in east



A positive phase of the Indian Ocean Dipole (IOD) may have already begun to play out, according to the Applications Laboratory of Jamstec, the Japanese national weather forecaster.

Positive phase of the IOD represents anomalous warming of the western basin of the Indian Ocean (adjoining the Arabian Sea).

This is supposed to have a favourable impact on a concurrent Indian monsoon.


The IOD phase will continue to evolve into the northern hemisphere autumn, according to the latest updates (July based outlook) of the forecaster made available just now.

However, it suggests that the favourable impact (enhanced rain) would be observed largely over the Bay of Bengal and the adjoining eastern parts of mainland India.

This is being attributed to the combined influence of the positive phase of the IOD and the strong El Nino conditions in the central and equatorial Pacific.


Already, there are signs that the north and northwestern parts of the Bay of Bengal are in an overdrive, pushing rainfall in an 'eastern India-first' mode, which is the natural course to take.

An existing low-pressure area having snaked in from the Bay has travelled west into north Madhya Pradesh and south Uttar Pradesh, where it has stopped in its tracks even while raining out all the way.

It continues to persist in the region even this morning, doing what it knows best — which is drive monsoon to a peak over west Madhya Pradesh, adjoining east Rajasthan, and the west coast, including Mumbai.


There is a forecast for a follow-up 'low' in the Bay, which should go well with the IOD outlook and its implications for the basin.

The Jamstec forecast has said apart from most parts of India, Europe, Africa, western Russia, South-East Asia, Northern South America, Mexico, Canada, and East Asia will too experience a warmer-than-normal conditions, going forward.

The August outlook for India points to excess rainfall for eastern parts of the country, while the rest of the country is likely to witness below-normal rainfall.


As for September and October, the excess will be confined to peninsular India. This goes to corroborate the known pattern of a productive and rainy northeast monsoon for the region during an El Nino.

According to the seasonally averaged rainfall prediction, northern India, Japan, Indonesia, Australia (particularly the north) and northern Brazil will experience drier-than-normal conditions over the next couple of months.

On the other hand, most parts of the Bay of Bengal, Baja California, and southern Brazil are likely to witness wetter-than-normal conditions, the Japanese forecaster said.

Published on July 21, 2015

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