Decay of Indian Ocean Dipole may help bring winter chill back to South

A long-lasting positive phase of the Indian Ocean Dipole (IOD) has decayed and the Indian Ocean returned to neutral, bringing the curtains down on an aggressively anomalous warming of the West Indian Ocean. The phenomenon, which began as early as in May and peaked in October, had engineered the successful rollout of the South-West and North-East monsoons in India.

Both the monsoons overstayed, delaying the sequential onset over Australia in the Southern Hemisphere, triggering an extended summer, a simmering drought and searing heat waves over the vast island-continent, ultimately fanning some of its worst bush fires, from September to this day.

South may feel the chill again

Over India, the rains from the North-East monsoon, which normally closes by the end of December, spilled over into early January, but the end of the warming phase of the West Indian Ocean may cut short the causative warm and moist easterly flows across the South Peninsula. It may also help bring back the early morning chill to the South Peninsula even as the skies clear up to align with the winter conditions with the land getting heated up later into the mornings and afternoons.

But the US National Centres for Environmental Prediction-Global Forecasts System model still sees the scope of isolated patches of rain creeping up the South-West coast (Kerala-Karnataka) from the South of Sri Lanka during the next couple of weeks. This could likely come about due to visitations by a couple of intense western disturbances delving deep South from their normal trajectory across North-West India.

Western disturbance

Meanwhile, an incoming western disturbance located on Tuesday over Afghanistan and preparing to enter Pakistan and North-West India, has already induced the formation of an offspring circulation over South-West Rajasthan.

It is intense western disturbances such as this that send out an offspring up front even as the parent bides its time at the rear. The offspring can create chaotic weather in the form of snow in the hills, thunderstorms, heavy rain and even hail in the plains of North-West India. Another western disturbance is expected to enter the region in the next four days.

The passage of the western disturbance will invite the colder north-westerly Arctic winds to fill the plains and bring down mercury levels, signalling cold wave conditions. The skies being cleared of clouds would also mean cold day conditions, when day temperatures are locked at a maximum of 16 degrees Celsius or below. These conditions should remain until the next western disturbance with its lower pressure, moisture up front, clouds and ascending warm air break the cold spell.

This is a normal pattern of events during typical winter conditions over North-West India, Central India, East and North-East India. Some of the cold can seep into Peninsular India depending on the track and sweep of the western disturbance.

COMMENT NOW