Monsoon unlikely to hit Delhi this month, may weaken in 7 days: IMD
The south-west monsoon is unlikely to hit Delhi, Haryana, Punjab, and some parts of Rajasthan till the end of the month, the Indian weather office said on Tuesday, further pushing back the expected arrival of the seasonal rains, which, just around 10 days ago, looked set to make an entry in the Capital almost a fortnight early, by June 15. Now, it will almost keep to the schedule it usually does, year after year.
The India Meteorological Department also added that a weak monsoon phase is commencing over central, Peninsular and northwest India during next seven days owing to unfavourable meteorological conditions. Still, almost all parts of the country have so far received excess rainfall. Till Monday, the country as a whole received 37% more rain than it usually does in June; there was a 76% excess in northwest India, 58% in central India, 24% over the southern peninsula, and 13% in east and northeast India.
The reason for the delay, according to IMD is a trough (an elongated area of low pressure) in the westerlies that have been persisting for the past 10 days. Normally, westerlies are weak in June as easterly monsoon winds pick up but this year, the trough in westerlies has been oscillating over northwest India, weakening the flow of the monsoon. Then, the mid latitude westerlies have strengthened again as a western disturbance (a cyclone originating in the mediterranean region) approached the Western Himalayan region on Monday.
Scientists said such strengthening of mid latitude westerlies is uncommon in June. “There were two anti-cyclones, one over Afghanistan and another north of Myanmar. There was a trough running from Jammu and Kashmir up to parts of Rajasthan which was oscillating but very slightly. The trough was persisting for ten days. In the next four to five days we do not expect any change in conditions because mid-latitude westerlies have strengthened further. This is the main reason why the monsoon is not able to progress beyond certain parts of Uttar Pradesh and Rajasthan. We cannot say when the monsoon will arrive in Delhi immediately. It will take time,” said Kuldeep Shrivastava, head, regional weather forecasting centre.
Normally two or three western disturbances impact the Western Himalayan region in June but their impact is limited to northern regions of Jammu and Kashmir. The mid latitude westerlies are impacting the entire northwest India this time.
The monsoon has so far covered most parts of the country except parts of Rajasthan, Delhi, Haryana and Punjab. But IMD said further progress of monsoon is unlikely in the next seven days. The northern limit monsoon continues to pass through Barmer, Bhilwara, Dholpur, Aligarh, Meerut, Ambala and Amritsar.
There are other why the monsoon is likely to weaken over the coming week, apart from the trough in the westerlies.
The Madden-Julian oscillation’s (MJO) location and amplitude strongly modulates the intensity of tropical convection and features such as low pressure systems over the north Indian Ocean. It is currently lying in Phase 1 (east Africa) with amplitude greater than 1 which is not favourable for enhancing the convection over north Indian Ocean region and hence monsoon rainfall activities, IMD said in a statement. MJO is an oceanic-atmospheric phenomenon which causes intra-seasonal variability in weather features.
Weather models also indicate that the mid latitude westerlies will be sweeping over north India in the coming week. A western disturbance is lying as a cyclonic circulation over north Pakistan and adjoining Jammu & Kashmir and a there is a trough in mid- and upper-tropospheric levels. These are not favourable for enhancing monsoon activity over central India and the plains of northwest India.
Winds over eastern and central parts of Arabian Sea have also weakened and are currently blowing at about 10-20 knots along the west coast. Such weak monsoonal winds are likely to prevail during the next seven days. The models also show a low probability of low pressure systems forming over core monsoon areas as well as over the north Bay of Bengal till June 30.
“Sometimes such variations happen when instead of monsoon winds, westerlies start dominating. The timing is very important because such large-scale feature variations can slowdown progress of monsoon. Rains in east and northeast India will continue because contribution of moisture and convection from Bay of Bengal is still active. We will update as soon as monsoon starts strengthening again,” explained RK Jenamani, senior scientist at national weather forecasting centre, IMD.
The normal date of monsoon onset over Delhi is June 27. This year, however, the onset is likely to be delayed. Earlier this month, IMD forecast that monsoon would set over Delhi June 15.