Clash of 2 weather systems behind late Sept rain in the Capital
The intense and unusual rain that Delhi has seen over the past two days is the result of a rare interaction of two weather systems — a western disturbance and a low-pressure system —scientists said, adding that this phenomenon may prolong the already-delayed withdrawal of monsoon.
The intense and unusual end-of-September rain that Delhi has seen over the past two days is the result of a rare interaction of two weather systems — a western disturbance and a low-pressure system — 250km southwest of the city, scientists said, adding that this phenomenon may prolong the already-delayed withdrawal of monsoon.
Thanks to these rare conditions, what is the final (and also generally the weakest) leg of the monsoon has this year turned out to be one of its most active phases with widespread and nearly continuous rainfall over the city in the past few days. Delhi received 5.6mm of rainfall on Wednesday and 31.2mm of rainfall till 5.30pm on Thursday.
The full withdrawal of the monsoon over Delhi, which is scheduled for September 25, is now expected to be delayed.
More rain is expected in the Capital over the weekend, though the quantum may reduce slightly, India Meteorological Department (IMD) officials said.
“There is an interaction between a western disturbance and remnants of a low-pressure area over northwestern Madhya Pradesh. This is happening around 250km southwest of Delhi. At the moment, it is a cyclonic circulation with very intense convergence. There is a lot of moisture supply from Arabian Sea which is continuing. There is a very gradual movement of the system, but it’s very slow. These conditions will continue for the next 24 to 36 hours but rainfall quantum will reduce from tomorrow,” explained RK Jenamani, senior scientist at IMD’s National Weather Forecasting Centre.
The effects of the phenomenon are being felt throughout India’s northwest.
“We can expect widespread rainfall over parts of Uttar Pradesh for the next three-four days. Rainfall has however reduced over west Rajasthan, Punjab, Jammu and Kashmir and Himachal Pradesh. Intense showers over Uttar Pradesh have led to a major reduction in rainfall deficiency over the region during the last few days of monsoon,” he added.
So far, monsoon has withdrawn from parts of southwest Rajasthan and adjoining Kutch on Tuesday, four days after the normal date (September 17) for withdrawal from northwest India. However, its withdrawal from other parts of northwest India remains delayed.
Withdrawal of monsoon is declared over a region when there is no rainfall for five consecutive days, an anticyclone is established in the lower troposphere, and there is considerable reduction in moisture content as inferred from satellite water vapour imageries.
As things stand, the country has seen 7% of excess rainfall so far this year, with south India experiencing 26% excess rain. East and northeast India has seen 17% deficiency, while northwest has so far experienced 3% deficiency, according to IMD data.
Delhi, however, recorded a 36% rain deficiency; Punjab 20%; Bihar 30%; Jharkhand 20% and Uttar Pradesh 33%. Until mid-September Uttar Pradesh had over 45% rain deficiency.
“Monsoon withdrawal has been delayed because of a very intense low-pressure system... There is a lot of moisture incursion from Arabian Sea as well. This is probably the last low-pressure system of this monsoon but weather activities will continue over Delhi till September 25,” said Mahesh Palawat, vice president, climate change and meteorology at Skymet Weather.
Although this low-pressure area has weakened slightly, the associated cyclonic circulation has settled over northwest Madhya Pradesh. At the same time, a trough is running from Bay of Bengal to Rajasthan, cutting across Odisha and Chhattisgarh, while a western disturbance is affecting the western Himalayas.
Under the influence of these systems, rainfall is going to be likely over a majority of northwest India, IMD has said.
Madhya Pradesh will likely get widespread rainfall and thunderstorms till Saturday. Light rain is likely over Uttarakhand, Haryana, Punjab, and parts of Uttar Pradesh and Rajasthan through Friday and Saturday. Rain is also likely over the northeast, with Assam, Meghalaya and Arunachal Pradesh getting isolated very heavy rainfall over the next day or two, IMD has said.