Monsoon starts to withdraw from parts of North-West

The surplus South-West monsoon of 2019 has started exiting from North-West India on Wednesday against the average date of September 1, making it the most delayed withdrawal in recorded history.

The most delayed withdrawal in the past years has been recorded in 1961 (October 1, 1961), followed by September 30 in 2007, an India Met Department (IMD) update said.

A seasonal anticyclone with clockwise direction of winds and sinking motion of air that in turn, increases pressure and drives away clouds, has started to establish itself over North-West India.

The increase in pressure does not allow clouds to form - as against cyclonic circulations with lower pressure and rising warm and moist air that cools to form clouds and rain - bringing in dry climes into the region.

Ahead of formation of the anticyclone, the IMD had indicated yesterday that the mercury levels would climb down, to establish autumnal weather that would later give into winter conditions.

Mercury levels had dipped below normal (-1.6 deg C to -3.0 deg C) at most places over Rajasthan and at many places over Jammu & Kashmir, Haryana, Chandigarh, and Delhi yesterday (Tuesday).

Western disturbances would then start crossing the border with increasing regularity, would modulate weather to make it alternatively warm and moist or cold and wintry.

Meanwhile, the IMD said on Wednesday the anticyclone has led to a reduction in moisture in the lower levels as also rainfall over some parts of Punjab, Haryana and North Rajasthan.

The withdrawal line passed through Kapurthala, Ambala, Karnal, and Churu with conditions becoming favourable for the exit of monsoon from more parts of North-West India during the next two days.

May pick speed

The withdrawal process is forecast to pick up speed and swiftly cover the remaining parts of North-West India and the adjoining the subsequent two to three days.

Elsewhere, the transitional monsoon weather from South-West to North-East will cause scattered to fairly widespread rainfall with isolated heavy falls over Peninsular India and East India until Thursday.

Associated churn in the atmosphere will trigger thunderstorms accompanied by lightning over North-East India during this period and over East India and Peninsular India during next two days.

Link: High pressure, low pressure illustrations

The 24 hours ending Wednesday morning saw rainfall (in cm) being recorded Kodaikanal -6; Shantiniketan and Hassan -5 each; Tezpur, Digha, Jamshedpur, Sambalpur and Alibag -4 each; Portblair, North Lakhimpur, Kolkata (Dum Dum)-3 each; and Deomali, Kohima, Burdwan, Midanapore, Balasore and Thiruvananthapuram -2 each.

Cyclonic whirls

Cyclonic circulations are positioned at vantage points over land while a trough crisscrosses the atmosphere facilitating the chaotic transitional weather over the East, North-East and Peninsular India.

On Wednesday, the IMD traced cyclonic circulations to over Haryana, North Coastal Andhra Pradesh, East-Central Arabian Sea off the Karnataka coast, and over East Assam.

Link: All India weather forecast bulletin

The trough - elongated reservoirs of moisture - linked North Coastal Andhra Pradesh to Comorin across Rayalaseema and Tamil Nadu.

Of these, the one over East-Central Arabian Sea off the Karnataka coast seem to have been put under watch by the Climate Prediction Centre of the US National Weather for signs of intensification over the next week or so.

If this forecast verifies, it would have a bearing on the arrival of North-East monsoon thanks to a band of easterlies to north-easterlies that it would be capable of streaming from the Bay and across Peninsular India.

As if on cue, an extended outlook by the IMD for three days from October 14 to 16 said that isolated to scattered rainfall might lash the South Peninsula and East and North-East India.

Isolated heavy falls have been forecast for Kerala and Coastal Karnataka as well.

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