Faulty monsoon forecast for Delhi: IMD blames ‘rare failure by prediction models’

India Meteorological Department on Monday blamed its failure in predicting New Delhi’s monsoon on numerical models. The national capital is reeling under scorching heat even as rains have hit neighbouring areas, such as Aligarh in Uttar Pradesh and Karnal in Haryana.

“Such type of failure by numerical models in prediction of monsoon advance over Delhi is rare and uncommon,” IMD said in a statement. “It is needless to mention that IMD has predicted well with high accuracy about the advance of monsoon over Delhi quite accurately in the recent past years and also the advance of monsoon over different parts of the country during the monsoon 2021 accurately about four to five days ahead.”

The weather department said it is monitoring the situation continuously and will provide regular updates on entry and advance of monsoon into the rest of northwest India, including Delhi.

Chronologically listing out its forecasts for north India, based on signals given out by numerical weather prediction (NWP) models, it said:

# Southwest monsoon continued its advance across the country till June 13 along with favourable atmospheric circulation and a low pressure system over Bay of Bengal after the entry of monsoon into Kerala on June 3.

# By June 13, it covered most parts of the country except northwest India. On the same day, numerical weather prediction (NWP) models suggested the favourable conditions with moist lower-level easterly winds reaching up to northwest part of the country. This may help further advance of monsoon into most of Madhya Pradesh; rest of Uttar Pradesh; Delhi; Haryana and Punjab during the next 48 hours, the models showed. A press release was issued accordingly indicating that monsoon is likely to advance into Delhi by June 15.

# On June 14, however, weather analysis based on satellite and NWP model consensus signalled advancement of a trough in mid-latitude westerly winds, leading to weakening of easterly winds over northwest India. “Due to adverse influence of this mid-latitude westerly winds, further advance of monsoon into remaining parts of northwest India including Delhi was not expected. Accordingly, IMD issued an updated press release on 14th June indicating that further advance of southwest Monsoon into remaining parts of northwest India including Delhi would be slow and delayed,” IMD said. This development of interaction with westerlies could not however be anticipated by the prediction models.

# On June 16, another press release was issued hinting delay in monsoon over Delhi and slow progress into some other parts of northwest India too. Accordingly, monsoon came into some parts of northwest India by June 19.

# “Since June 20, there has been no further advancement of monsoon due to weakening of or break in monsoon conditions. “Regular press releases were issued and updated to media from time to time on 22, 24, 26 and 30 June and 1 July indicating such delays in monsoon advance into remaining parts of northwest India including Delhi and weak/break monsoon conditions over the country,” IMD said. It clarified, the delay in monsoon advance was mainly due to (a) no formation of low pressure area over Bay of Bengal, (b) Absence of monsoon trough at mean sea level near to Delhi, (c) Five-six western disturbances moved west to east across North India which dominated over the monsoon easterlies.

# On July 5, another press release on monsoon status was issued predicting that monsoon would enter into remaining parts of west Uttar Pradesh, some more parts of Punjab, Haryana and Rajasthan and Delhi around July 10.

# The latest model analysis also showed that the moist easterly winds in lower level from Bay of Bengal would spread across northwest India covering Punjab and Haryana by July 10 resulting in advance of monsoon and a notched up rainfall activity over the northwest India including Delhi.

# The moist easterly winds have accordingly spread into northwest India. After July 8, easterly winds at lower levels were established along the foothills and from July 9, easterly winds were established over Northwest India planes. These moisture-laden winds have resulted in the increase in cloudiness and relative humidity. “It also led to revival of monsoon over the region and occurrence of fairly widespread/widespread rainfall activity over east Rajasthan, HP, Uttarakhand, J&K and scattered rainfall over Punjab and west Rajasthan. However, it did not cause significant rainfall activity over Delhi even though, there was rainfall activity over neighbouring places around Delhi,” the IMD said.