Thursday, September 08, 2011

Signs of a developing positive Indian Ocean Dipole (IOD) event

Amid growing signs of a developing positive Indian Ocean Dipole (IOD) event, global weather models have warned about the possibility of continued heavy rain over western India for two more weeks.
This is even as the European Centre for Medium-Range Weather Forecasts saw the next low-pressure area to materialise over south-west and adjoining west-central Bay of Bengal by mid-week next week.
An IOD event refers to the seesawing of sea-surface temperatures (SSTs) in the western and eastern basins of the Indian Ocean.


The IOD is positive when the warmth is more to the west, and vice versa. SSTs are expected to stay at enhanced levels during the period until September 20. A positive IOD event has been seen to boost a concurrent Indian monsoon.
The US National Centres for Environmental Prediction suggests that rains could get heavier towards east India during the latter part of the period, and even going until September 23.
Combined with a suspected La Nina event in the making, which is a magnified mock-up of the Indian Ocean event in the larger Pacific Ocean, the positive IOD would only add to the intensity of the precipitation.


A La Nina-positive IOD combine was witnessed during the years of 2006 to 2008, a rarity in itself, and which underpinned normal to moderately surplus Indian monsoon.
The Climate Prediction Centre of the US National Weather Services says in its latest outlook that the monsoon flows are likely to stay enhanced during the next two weeks.
During week-1 (September 7 to13), this would trigger enhanced rainfall in western India, the Bay of Bengal, Southeast Asia, and the South China Sea. This is attributed mainly to above average SSTs in the western equatorial Indian Ocean.


During week-2 (September 14 to 20), model guidance and above average sea surface temperatures favour enhanced convection in the western Indian Ocean.
But the rains are seen covering more area during this week, with monsoon flow expected to remain enhanced across most of India (including the peninsula), the Bay of Bengal, and parts of South-east Asia. 


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